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Fertiliser nitrogen use in Australia has increased from 35 Gg N in 1961 to 972 Gg N in 2002, and most of the nitrogen is used for growing cereals. However, the nitrogen is not used efficiently, and wheat plants, for example, assimilated only 41% of the nitrogen applied. This review confirms that the efficiency of fertiliser nitrogen can be improved through management practices which increase the crop's ability to compete with loss processes. However, the results of the review suggest that management practices alone will not prevent all losses (e.g. by denitrification), and it may be necessary to use enhanced efficiency fertilisers, such as controlled release products, and urease and nitrification inhibitors, to obtain a marked improvement in efficiency. Some of these products (e.g. nitrification inhibitors) when used in Australian agriculture have increased yield or reduced nitrogen loss in irrigated wheat, maize and cotton, and flooded rice, but most of the information concerning the use of enhanced efficiency fertilisers to reduce nitrogen loss to the environment has come from other countries. The potential role of enhanced efficiency fertilisers to increase yield in the various agricultural industries and prevent contamination of the environment in Australia is discussed.
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Prospects of improving efciency of fertiliser nitrogen in Australian
agriculture: a review of enhanced efciency fertilisers
D. Chen
A,D
, H. Suter
A
, A. Islam
A
, R. Edis
A
, J. R. Freney
A,B
, and C. N. Walker
C
A
School of Resource Management, Faculty of Land and Food Resources, The University of Melbourne,
Vic. 3010, Australia.
B
CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia.
C
Incitec Pivot Ltd, PO Box 54, North Geelong, Vic. 3215, Australia.
D
Corresponding author. Email: delichen@unimelb.edu.au
Abstract. Fertiliser nitrogen use in Australia has increased from 35 Gg N in 1961 to 972 Gg N in 2002, and most of the
nitrogen is used for growing cereals. However, the nitrogen is not used efciently, and wheat plants, for example,
assimilated only 41% of the nitrogen applied. This review conrms that the efciency of fertiliser nitrogen can be improved
through management practices which increase the crops ability to compete with loss processes. However, the results of the
review suggest that management practices alone will not prevent all losses (e.g. by denitrication), and it may be necessary
to use enhanced efciency fertilisers, such as controlled release products, and urease and nitrication inhibitors, to obtain a
marked improvement in efciency. Some of these products (e.g. nitrication inhibitors) when used in Australian agriculture
have increased yield or reduced nitrogen loss in irrigated wheat, maize and cotton, and ooded rice, but most of the
information concerning the use of enhanced efciency fertilisers to reduce nitrogen loss to the environment has come from
other countries. The potential role of enhanced efciency fertilisers to increase yield in the various agricultural industries
and prevent contamination of the environment in Australia is discussed.
Additional keywords: controlled release, urease inhibitors, nitrication inhibitors, mitigation, greenhouse gases.
Introduction
As the intensity of agricultural production in Australia increases
to keep pace with population growth, the need for food and bre,
and maintaining prot margin, fertiliser nitrogen use has
increased from 35 Gg N in 1961 to 972 Gg N in 2002 (FAO
2007; Fig. 1). This fertiliser nitrogen is used mostly on cereals
(702 Gg N), sugarcane, pasture, horticulture, cotton, and
oilseeds. Rates of application varied from 2.5 to 229 kg N/ha
(Table 1).
However, when fertiliser nitrogen is applied to soil it is not
used efciently, and the plant seldom assimilates >50% of the
nitrogen added. Plant uptake for a range of crops and pastures in
Australia varies from 6 to 59% of the nitrogen applied
(Table 2). In general, bananas and ooded rice were the least
efcient of the crops studied (617%). The mean recovery of
applied nitrogen in Australian dryland wheat was 41%
(2259%), which is marginally better than the estimated
worldwide efciency of nitrogen for cereals of 33%
(Raun and Johnson 1999).
One of the main reasons for the poor efciency of fertiliser
nitrogen use is that much of the nitrogen applied (up to 92%) can
be lost from the plantsoil system (Table 3). Fertiliser nitrogen
can be lost by ammonia volatilisation, during nitrication, and
by leaching, erosion, runoff, and denitrication, and the relative
importance of these processes can vary widely depending on
the agroecosystem, fertiliser form, and method of application.
For example, ammonia volatilisation was important when urea
was applied to sugarcane elds covered with plant residues,
while denitrication was the major loss process when anhydrous
ammonia was drilled into irrigated cotton (Table 3). In most of
the systems studied in Australia, erosion and runoff were
controlled and leaching was small.
Lost nitrogen represents a serious economic loss to farmers,
but the impact of the lost nitrogen on the environment and
human health is equally, if not more, important. As pointed out
above gaseous emissions of nitrogen via ammonia volatilisation,
nitrication, and denitrication are the dominant mechanisms
for the loss of fertiliser nitrogen from Australian
agroecosystems. These processes result in the release of
ammonia, nitric oxide, and the greenhouse gas nitrous oxide
into the atmosphere. Agriculture is the main source of nitrous
oxide in Australia, contributing 67 Gg in 2005 (AGO 2007);
using IPCC (1997) guidelines it is calculated that 21 Gg of this
comes from fertiliser nitrogen. In addition to the effect on global
warming, the nitrogen gases produced from fertiliser can acidify
soils, eutrophy lakes, rivers, and estuaries, decrease biodiversity
in terrestrial ecosystems, affect atmospheric visibility, reduce the
stratospheric ozone layer that protects the Earth from harmful
ultraviolet radiation, and increase ozone concentrations in the
troposphere with consequent health effects (Peoples et al. 2004).
Mitigation strategies aimed at reducing nitrogen loss are
variable and can range from management practices through to
CSIRO 2008 10.1071/SR07197 0004-9573/08/040289
CSIRO PUBLISHING Review
www.publish.csiro.au/journals/ajsr Australian Journal of Soil Research, 2008, 46, 289301
the development of new technologies. New technologies include
the use of products such as controlled release fertilisers and
urease and nitrication inhibitors. Many of these products have
been in some use for decades, with controlled release fertilisers
commonly used in the nursery industry and inhibitors used for
research purposes, yet their use in agricultural situations is
relatively new and of particular interest in light of current
concerns regarding greenhouse gas emissions.
The objective of this paper is to provide a review of the
current literature on improving the efcacy of nitrogen fertilisers
through the use of controlled release coatings and urease and
nitrication inhibitors, concentrating specically on work
carried out in Australia.
Approaches to improve efciency
The processes that generate nitrogen loss from soil are controlled
directly by factors such as nitrogen availability and moisture,
and indirectly by environmental or management factors (Granli
and Bøckman 1994). Some of the factors that control loss such
as soil type, rainfall, radiation, and temperature are outside the
farmers control, but there are others that the farmer can
inuence. These manageable factors include fertiliser type,
amount, method and time of application, water status
(controlled by irrigation and drainage), soil pH (adjusted by
application of lime), and soil compaction (tillage and
trafcking).
In general, nitrogen loss can be decreased by management
practices which increase the crops ability to compete with the
loss processes (Minami 1997). The approaches that have been
suggested for improving the efciency of fertiliser nitrogen
include the following:
(i) using soil and plant testing to make best use of
indigenous nitrogen (Johnkutty and Palaniappan 1996;
Dobermann and Cassman 2004);
(ii) using the optimal form, rate, method and time of
application of the fertiliser (Strong et al. 1992; Smith
et al. 1997);
(iii) incorporation or deep placement of fertiliser (De Datta
et al. 1989; Cai et al. 2002; Roy and Hammond 2004);
(iv) using split applicationsseveral applications of small
amounts of fertiliser during the growing season are more
effective than one large dose at the beginning of the
season (Hooper 2004);
(v) minimising application in the wet season to reduce
leaching and denitrication (McTaggart et al. 1994);
(vi) delaying the supply of fertiliser until a substantial canopy
has developed (Humphreys et al. 1988),
(vii) using foliar application (Smith et al. 1991); and
(viii) using inter seasonal cover crops to minimise the
accumulation of nitrate during fallow periods
(McLenaghen et al. 1996; Wagner-Riddle and Thurtell
1998; Cameron et al. 2002).
Where denitrication is likely to be the main process responsible
for nitrogen loss, nitrate forms of fertiliser should not be used.
Thus, matching the type of fertiliser with rainfall and moisture
conditions in the soil could result in appreciable reductions in
nitrogen loss (McTaggart et al. 1994). This is likely to be more
benecial and easier to manage than attempting to maintain a
balance between appropriate water management and limiting
denitrication or nitrate leaching. For example, trickle or drip
irrigation systems which allow delivery of nitrogen to the area
of maximum crop uptake enable the application rate to be
matched to the plantsrequirements. With careful operation,
trickle systems can reduce deep percolation, runoff, and
denitrication (Doerge et al. 1991). The aim of better water
management should be to reduce denitrication by ensuring that
the water-lled pore space of the soil does not exceed 60%
(Smith et al. 1997; Mosier et al. 2002).
Returning crop residues to the soil instead of burning them
allows reuse of the nitrogen contained in the residues.
Incorporated residues can also improve soil structure, and
reduce ammonia volatilisation by inuencing the conditions
of the underlying soil, and by acting as a medium through
which ammonia must pass before being lost to the atmosphere
(Aulakh et al. 1991; Freney et al. 1992b). Incorporating residues
with high C/N ratio into soils will immobilise mineral nitrogen
which can become available later when mineralised (Aulakh
et al. 1991).
Optimising plant growth and uptake of nitrogen through
management of the plants total nutrient requirements is
another means of increasing nitrogen use efciency. The
supply of one nutrient affects the absorption, distribution, or
1960 1970 1980 1990 2000
0
200
400
600
800
1000
1200
Year
Fertiliser nitrogen (Gg)
Fig. 1. Fertiliser used in Australia during the period 19602002.
Table 1. Fertiliser nitrogen used for crops and pasture in Australia
in 2000 (FAO, IFA, IFDC, IPI, PPI 2002)
Commodity Fertiliser consumption Application rate
(Gg N) (kg N/ha)
Cereals 702 42.9
Sugarcane 96 229.1
Pasture 75 2.5
Horticulture 71 187.8
Cotton 56 121.2
Oilseeds 55 12.8
Total 1055
290 Australian Journal of Soil Research D. Chen et al.
function of another nutrient, so that insufcient amounts of
plant-available phosphorus, sulfur, potassium, or other nutrient
will reduce nitrogen use efciency. For example, nitrogen
recovery in phosphorus-decient corn was <40%, whereas it
was 75% when adequate phosphorus was supplied (Oberle and
Keeney 1990).
Site-specic nitrogen management is used to synchronise the
supply and demand of nitrogen, and it can be used to manage
nitrogen in labour-intensive, small-scale farming or highly
mechanised, large-scale production elds (Dobermann and
Cassman 2004). Optimum nitrogen rates vary spatially and
seasonally; thus, diagnostic tools are required to assess soil or
crop nitrogen status during the growing season to make
decisions on the amount of nitrogen to be applied (Schröeder
et al. 2000). One diagnostic measure is leaf greenness, and
several techniques exist to measure this, including near-infrared
leaf nitrogen analysis, chlorophyll meters, leaf colour charts,
crop canopy reectance sensors, and remote sensing (Giller et al.
2004). Signicant increases in nitrogen use efciency have been
achieved through reductions in nitrogen use.
Decision support systems (DSS), based on comprehensive
and process-based agro-ecosystem models, for optimum
nitrogen fertiliser management have also been used recently.
The advantage of such systems is the ability to integrate bio-
physical variables/interacting processes and management
practices and economicalenvironmental considerations. The
best management practices can be identied by simulating the
combination of different management practices, such as
interaction of nitrogen application rates and time with
irrigation rate and time, and trade-off between economical
and environmental interests. The GIS-based DSS for fertiliser
application and irrigation for North China Plain, derived from
the Water and Nitrogen Management Model (WNMM), has
signicantly assisted the dissemination of the best management
fertiliser nitrogen practices with substantial economical impact
(Chen et al. 2006).
Table 3. Nitrogen lost from agricultural systems in Australia (% of applied)
Crop and location Loss References
Volatilised Denitried Total
Bananas: East Palmerston, Qld 20 5 25 Prasertsak et al. (2001a)
Cotton (irrigated): Narrabri, NSW 0 4392 4392 Freney et al. (1993),
Humphreys et al. (1990)
Pasture:
Millaa Millaa, Qld 20 20 40 Prasertsak et al. (2001b)
Ellinbank, Vic. 3257 1315 4770 Eckard et al. (2003)
Rice (ooded): Grifth, NSW 011 1556 4056 Simpson et al. (1984, 1985),
Keerthisinghe et al. (1993)
Sugarcane:
Mackay, Qld 0 3962 3962 Chapman et al. (1991)
South Johnstone, Qld 637 2240 4659 Prasertsak et al. (2002)
Sunowers: Tatura, Vic. 6 29 35 Smith et al. (1988)
Wheat (dryland): Hanwood, Murrami,
Widgelli, Willurah, Wumbulgal,
Yanco, NSW; Birchip, Chinkapook,
Elmore, Wunghnu, Diggers Rest, Vic.
124 227 1240 Bacon and Freney (1989),
P. E. Bacon, J. R. Freney,
unpublished data
Wheat (irrigated): Tatura, Vic. 0 50 50 Freney et al. (1992a)
Table 2. Recovery of fertiliser nitrogen by crops and pastures in Australia
Crop and location Recovery (% of applied) References
Plant Soil Plant + soil
Bananas: East Palmerston, Qld 15 60 75 Prasertsak et al. (2001a)
Cotton (irrigated): Narrabri, NSW 2729 828 857 Freney et al. (1993),
Humphreys et al. (1990)
Pasture: Millaa Millaa, Qld 42 18 60 Prasertsak et al. (2001b)
Rice (ooded): Grifth, NSW 617 3748 4460 Simpson et al. (1984, 1985),
Keerthisinghe et al. (1993)
Sugarcane:
Mackay, Qld 1438 2341 3861 Chapman et al. (1991)
South Johnstone, Qld 1929 2225 4154 Prasertsak et al. (2002)
Sunowers: Tatura, Vic. 35 30 65 Smith et al. (1988)
Wheat (dryland): Hanwood, Murrami,
Widgelli, Willurah, Wumbulgal, Yanco,
NSW; Birchip, Chinkapook, Elmore,
Wunghnu, Diggers Rest, Vic.
2259 2054 6088 Bacon and Freney (1989),
P. E. Bacon, J. R. Freney,
unpublished data
Wheat (irrigated): Tatura, Vic. 25 25 50 Freney et al. (1992a)
Improving efciency of fertiliser nitrogen Australian Journal of Soil Research 291
Enhanced efciency fertilisers
While the techniques described above have the potential to
increase the effectiveness of applied nitrogen, considerable N
losses still occur. For example, in ooded rice the time of
application had a big effect on the agronomic efciency of
fertiliser nitrogen and ammonia volatilisation, but even with the
best system devised, around 40% of the applied nitrogen was
still lost by ammonia volatilisation, denitrication, or leaching
(Bacon and Heenan 1987; Humphreys et al. 1988). In order to
further reduce loss by these processes, alternative fertilisation
techniques, such as the use of controlled release fertilisers,
urease inhibitors, and nitrication inhibitors, need to be
considered. These can be collectively referred to as enhanced
efciency fertilisers.
There have been numerous studies on enhanced
efciency fertilisers, either used alone or in combination
in agroecosystems, with highly variable efciencies
demonstrated (Smith et al. 1997; Trenkel 1997; Zerulla et al.
2001; Drost et al. 2002; Singh et al. 2004; Watson 2005).
The high variability in effectiveness is often due to a lack of
understanding of the interaction of these chemicals with soil and
environmental variables (Mosier et al. 2002). For example, the
nitrication inhibitor dicyandiamide (DCD) was shown to be a
very effective nitrication inhibitor under cold climatic
conditions, but is less effective in warm/hot and wet climates
due to its rapid decomposition (Zerulla et al. 2001; Singh et al.
2004; Di and Cameron 2004b; Hatch et al. 2005). Most eld
studies have concentrated on the effect on production
(grain yield or biomass) and few have considered gaseous
nitrogen loss and nitrate leaching. While many studies have
been carried out in other countries, few have been conducted in
Australia. Thus, there is a need to evaluate the effectiveness
of various formulations and strategies under conditions
applicable to Australias major agroecological zones for
fertiliser manufacturers and farmers.
Controlled release fertilisers
The supply of nitrogen by a single application of slow or
controlled-release fertiliser should satisfy plant requirements
and maintain low concentrations of mineral nitrogen in the
soil throughout the growing season. As a result, labour and
application costs should be low, nitrogen loss should be
minimised, nitrogen use efciency should increase, and yields
should be improved.
Many different controlled release forms of nitrogen
have been suggested (Peoples et al. 1995), and considerable
advances have been made in the formulation of these materials.
Shaviv (2005a, 2005b) has classied these fertilisers into 3
main types:
(i) inorganic low solubility compounds (e.g. magnesium
ammonium phosphate);
(ii) organic low solubility compounds (e.g. urea formaldehyde
and isobutylidenediurea);
(iii) coated materials in which a physical barrier controls the
release (e.g. granules coated with hydrophobic polymers,
or matrices in which the soluble fertiliser is dispersed so
the dissolution of the fertiliser is restricted).
The coated fertilisers can be further divided into those coated
with inorganic material (e.g. sulfur-coated urea), sulfur-coated
fertiliser, which is further coated with an organic polymer
(e.g. polymer-coated sulfur-coated urea), and those coated
with organic polymers, viz. thermosetting resin-coated
fertilisers and thermoplastic polymer-coated fertilisers.
Sulfur-coated urea was developed in the 1960s by the
National Fertilizer Development Center and used with mixed
success in a variety of applications, e.g. ooded rice (Prasad and
De Datta 1979) and wheat (Mason 1985). Sulfur coatings
provide highly variable nitrogen release patterns depending
upon coating damage that might occur, and as much as one-
third can be released instantaneously Addition of a polymer
coating to sulfur-coated urea signicantly improved its
performance. Polymer sulfur-coated urea has improved
ryegrass and bluegrass quality in 2 Pacic north-west
climates (Miltner et al. 2004) and reduced leaching loss to
only 1.7% of the applied nitrogen after application to turf
lawn in southern New England (Guillard and Kopp 2004).
The main thermosetting resin-coated fertilisers are the alkyd-
type resins (e.g. Osmocote) and those with polyurethane-like
coatings such as Polyon, and Multicote (Trenkel 1997; Shaviv
2005a). Nutrient release from these materials is controlled by the
coating thickness (Trenkel 1997; Shaviv 2005a). According to
Shoji and Gandeza (1992), the most accurate controlled release
of nutrients is provided by the polyolen thermoplastic-coated
fertilisers (e.g. Meister) developed by Chisso-Asahi Fertilizer
Co., Japan. Fertiliser release is controlled by coating
fertiliser particles with polyolens, such as polyethylene and
polypropylene, which have low water permeability, and
ethylene vinyl acetate, which has high water permeability.
The pattern of nutrient release from coated fertilisers can be
parabolic, linear, or sigmoidal and long- or short-term (Shaviv
2005a). Nitrogen uptake of seasonal crops and perennial species
is generally sigmoidal (Shoji and Kanno 1994; Shoji et al. 2001;
Shaviv 2005a). Because of the variety of polyolen-coated
fertilisers available it is now possible to use computers to
program fertiliser release patterns to match the specic
requirements of a crop, and Shoji (2005) illustrates how this
can be used to supply nitrogen at the times of peak demand for
ooded rice.
Use of polyolen-coated urea instead of uncoated fertiliser
has resulted in increased yields and nitrogen use efciency in a
range of crops including potatoes, rice, and direct-seeded onions
(Mikkelsen et al. 1994; Shoji and Kanno 1994; Shoji et al. 2001;
Drost et al. 2002; Fashola et al. 2002; Shoji 2005; Wu et al.
2005). Large reductions in the emission of nitrous oxide have
also been achieved using polyolen-coated ammonium nitrate
(Minami 1994), polyolen-coated ammonium sulfate
(Nutricote; Smith et al. 1997), and polyolen-coated urea
(Shoji et al. 2001) instead of uncoated nitrogen fertiliser.
However, no yield effect was found in irrigated cotton in
Australia by using polyolen-coated urea, although there
were signicant impacts on N uptake and mineral N (urea,
ammonium, and nitrate) dynamics (Chen et al. 2008).
Ammonium-based fertilisers have been coated with
polyolens for use in vegetable growing to prevent the
build-up of nitrate, which affects quality and may constitute a
health risk (Matsumoto 1991; Takebe et al. 1996; Shoji 2005;
292 Australian Journal of Soil Research D. Chen et al.
Wang et al. 2005). A further decrease in nitrate uptake by
vegetables was achieved by adding the nitrication inhibitor
DCD to the fertiliser before coating the mixture with polyolen
(Mimaki 2003).
However, it has been pointed out that use of controlled
release fertilisers may result in nitrogen, in excess of the
crops requirements, remaining in the soil after harvest. This
nitrogen may then be lost to the environment in the same manner
as uncoated fertiliser (Delgado and Mosier 1996).
The use of controlled-release fertilisers in agriculture is still
limited in spite of the technological developments and
availability. Only about 10% of the total production is
consumed in agriculture, and the remainder is used for lawns,
golf courses, fruit trees, and vegetables (Shaviv 2005a). The
main reason for the limited use seems to be the high cost,
which may be 310 times the cost of conventional fertiliser
(Shaviv 2000).
Urease inhibitors
Urea has become the most widely used form of fertiliser
nitrogen, because it is the least expensive form of fertiliser
available, and its high nitrogen content (46%) means lower
transportation costs. Globally in developed countries urea
consumption has stabilised at around 30 Mt, while in
developing countries consumption is still increasing
dramatically and was around 55 Mt in 2002 (IFA 2006).
However, it has the disadvantage that considerable losses of
nitrogen can occur if the urea is not incorporated into soil soon
after application. Losses have ranged from negligible amounts to
>50% of the nitrogen applied, depending upon fertiliser practice
and environmental conditions (Peoples et al. 1995; Cai et al.
2002). The loss occurs by ammonia volatilisation after the urea is
converted to ammonia at the soil surface by reaction with
the enzyme urease. One approach to decreasing ammonia
volatilisation is to nd compounds that inhibit urease activity,
thus allowing the urea to move into the soil before hydrolysis.
The ammonia then released would be retained by the soil.
A large number of compounds with differing characteristics
have been tested for their ability to inhibit urease activity
(Medina and Radel 1988; Watson 2000, 2005; Kiss and
Simihaian 2002). Some inhibit the enzyme by reacting with
active sites on the enzyme or a key functional group elsewhere in
the molecule, or by changing the conformation of the active site.
Many organic and inorganic compounds and metal ions
inhibit urease by reacting with the sulfhydryl groups in the
enzyme (e.g. mercapto compounds), others by complexing with
nickel in the active site (e.g. hydroxamates), some by reacting
with the carboxylic acid group (e.g. arylorganoboron
compounds), and others because they are structural analogues
of urea (e.g. thiourea, methyl urea, and phosphoryl di- and
triamides) (Medina and Radel 1988).
The most effective compounds for the inhibition of urease
activity appear to be the phosphoryl amides (e.g. N-(n-butyl)
phosphoric triamide and cyclohexylphosphoric triamide (Chai
and Bremner 1987; Keerthisinghe and Blakely 1995; Byrnes
and Freney 1995), although hydroquinone and 2, 5-dimethyl
p-benzoquinone can provide inhibition at high concentrations
(Tomlinson 1970; Xu et al. 2005).
A host of natural products have been tested for their ability to
inhibit urease activity, including coal and peat; humic
substances; lignins and tannins; plant residues and extracts
containing polyphenols and saponins; neem cake, oil, and
extracts; karanja cake and mahua cake; and microbial
products (Kiss and Simihaian 2002). In India the press cake
from the production of neem (Azadirachta indica) oil has been
shown to inhibit urease activity (Trenkel 1997), and when it was
used to coat urea it reduced loss of nitrogen and improved
nitrogen use efciency (John et al. 1989). Patra et al. (2006)
showed that the natural essential oil, dementholised oil, and
terpenes of peppermint (Mentha spicata) signicantly retarded
soil urease activity. Natural inhibitors of urease activity have
also been found in Artemisia annua (Patra et al. 2002),
Ranunculus repens (Khan et al. 2006), and Aspergillus
ochraccus (Lin et al. 1997).
The compound which has been most widely tested for its
capacity to reduce ammonia loss from urea is N-(n-butyl)
thiophosphoric triamide (Trenkel 1997; Singh et al. 2004;
Watson 2005). However, like the other thiophosphoryl
triamides it is not a urease inhibitor. The thio compounds
are the precursors of oxygen analogues which are the
actual inhibitors. Numerous tests of the pure thio compounds
in vitro have shown their total ineffectiveness. The thio
compounds have to be converted to the oxygen analogues
on contact with soil or other material before inhibition can
occur (McCarty et al. 1989; Creason et al. 1990). It might
seem to be more logical to market the oxygen analogue of
N-(n-butyl) thiophosphoric triamide (viz. N-(n-butyl)
phosphoric triamide), but the oxygen analogue is not
sufciently stable for it to be packaged and distributed for
commercial application (Incitec Pivot, pers. comm.).
N-(n-butyl) thiophosphoric triamide, on the other hand, seems
to be quite stable (Hendrickson and Douglass 1993) although
its effectiveness is controlled by temperature (Chai and
Bremner 1987; Carmona et al. 1990). The results of Carmona
et al. (1990) indicate that higher concentrations of N-(n-butyl)
thiophosphoric triamide will be required to prevent ammonia
loss from warm soils than for temperate soils.
Watson et al. (1994a, 1994b) found N-(n-butyl)
thiophosphoric triamide very effective at low concentrations
(0.01% of applied urea nitrogen) for reducing ammonia
volatilisation (by ~50%) in eld trials on temperate
grassland. Its use also signicantly delayed and reduced
ammonia and nitrous oxide emissions from soil after
application of urea, urine, and urea ammonium nitrate
(Bronson et al. 1989b; Schlegel 1991; Grant et al. 1996;
Wang and Douglas 1996; Singh et al. 2004) and produced
signicant improvements in nitrogen use efciency of
corn following application of urea ammonium nitrate
(Fox and Piekielek 1993). In 21 upland eld experiments,
treating urea with N-(n-butyl) thiophosphoric triamide
increased grain yields of maize by an average of 750 kg/ha
(Bronson et al. 1989b). An additional 80 kg N/ha would
need to be applied to obtain that increase in yield
(Byrnes and Freney 1995). Similar positive results were
reported by Hendrickson (1992) for maize fertilised with
urea or urea ammonium nitrate in 78 trials conducted in the
USA between 1984 and 1989.
Improving efciency of fertiliser nitrogen Australian Journal of Soil Research 293
Both N-(n-butyl) thiophosphoric triamide and cyclohexyl
phosphoric triamide have been used successfully to control
ammonia emission from animal wastes, to prevent
environmental damage, and to produce a more balanced
nitrogen/phosphorus fertiliser from manure (Varel 1997;
Varel et al. 1999).
Nitrication inhibitors
Maintaining nitrogen in the ammonium form in soil would
prevent its loss by both nitrication and denitrication. One
method of doing this is to add a nitrication inhibitor with the
fertiliser. This prevents or slows the microbial conversion of
ammonium to nitrate and hence the leaching of nitrate and
production of nitric oxide, and nitrous oxide by both
nitrication and denitrication. While this technique does not
always produce increased crop yields it does provide a tool for
managing nitrate leaching and nitrous oxide production
(Edmeades 2004).
Reliable data on the use of nitrication inhibitors in different
crops and regions are not available. Surveys of USA farmers
indicate that at present about 9% of the national maize area is
treated with nitrication inhibitors, and this proportion has
remained unchanged in recent years (Christensen 2002).
Many chemicals have been tested as nitrication inhibitors,
but few are commercially available (Table 4) or have proven to
be agronomically and economically effective (Slangen and
Kerkhoff 1984; Prasad and Power 1995; McCarty 1999; Frye
2005). The persistence and behaviour of nitrication inhibitors
in soil is determined by diffusion into the atmosphere,
decomposition or degradation, differential movement in soils,
sorption on clay or organic matter (Slangen and Kerkhoff 1984),
and by environmental and edaphic factors, such as temperature,
moisture, and soil texture (Prasad and Power 1995). While
progress is being made towards understanding the mode of
action of many inhibitors of ammonia oxidation, little is
known about the action of others such as the heterocyclic
nitrogen compounds (McCarty 1999).
Of the inhibitors listed in Table 4, the most extensively
studied products are nitrapyrin, DCD, and more recently
3,4-dimethylpyrazole phosphate (Goos and Johnson 1999;
Dittert et al. 2001; Pasda et al. 2001; Weiske et al. 2001a,
2001b; Zerulla et al. 2001; Calderon et al. 2005; Chao et al.
2005; Islam et al. 2007a, 2007b).
Nitrapyrin is often ineffective because of sorption on soil
colloids, hydrolysis, and loss by volatilisation (Hoeft 1984; Liu
et al. 1984), but it has reduced nitrogen losses and resulted in
increased plant nitrogen uptake (Fillery and De Datta 1986;
Chen et al. 1998a, 1998b). When Wolt (2004) evaluated the
performance of nitrapyrin across research trials conducted in
diverse environments over many years in Midwestern USA, he
found that, on average, nitrapyrin increased corn yield by 7%
and soil retention of nitrogen by 28%. It also decreased nitrogen
leaching by 16% and nitrous oxide emission by 51%.
Dicyandiamide inhibited nitrication when ammoniacal
fertilisers were applied to eld crops and vegetables (Frye
et al. 1989; Frye 2005) with the result that nitrogen remained
longer in the soil in the ammonium form (Irigoyen et al. 2003).
Yield increases have been obtained when DCD was applied to
pastures (Di and Cameron 2002; Smith et al. 2005) and various
cropping systems, e.g. maize (Ball-Coelho and Roy 1999),
wheat (Rao 1996; Sharma and Kumar 1998; Rao and
Popham 1999), and maizewheat (Sharma and Prasad 1996).
However, application of DCD does not always lead to yield
increases (Mason 1987; Dachler 1993; Frye 2005) and in some
cases can have deleterious effects on plant growth (Macadam
et al. 2003). Yield increases usually occurred at low fertiliser
application rates (Frye 2005).
Leaching of nitrate can be signicantly reduced by addition
of DCD (Ball-Coelho and Roy 1999; Serna et al. 2000; Di and
Cameron 2002, 2004a). Treatment of urine patches on a ne
sandy loam in New Zealand with DCD reduced nitrate leaching
losses from 85 to 2022 kg N/ha.year (Di and Cameron 2002,
2004a). The benecial effect of the DCD was increased beyond
the saving of nitrogen because it also reduced leaching of the
cations associated with nitrate, calcium by 3856% and
magnesium by 2142% (Di and Cameron 2004a, 2004c)
Because DCD effectively retards nitrication, when it is
added to soil along with ammonium based fertilisers,
emissions of nitric oxide and nitrous oxide are substantially
reduced compared with fertiliser alone (Majumdar et al. 2000;
Shoji et al. 2001; Vallejo et al. 2001; Singh et al. 2004; Hatch
et al. 2005; Merino et al. 2005;). For example, Skiba et al.
(1993) showed that addition of DCD reduced nitric oxide
emission by about 92% and nitrous oxide emission by 40%.
Signicant reductions have also been reported for DCD-treated
pig slurry (Vallejo et al. 2005) and DCD-treated animal urine
patches in grazed perennial ryegrasswhite clover pastures (Di
and Cameron 2003). Di and Cameron (2003) showed that
repeated applications of DCD offered no advantage over a
single application of DCD immediately after urine deposition.
However, the effect of DCD on reducing the rate of
nitrication in soil is variable and in some cases no effect on
nitrate leaching was obtained (Davies and Williams 1995;
Table 4. Compounds produced commercially as nitrication inhibitors (modied from Nelson and Huber 2001)
Chemical name Common or trade name Manufacturer
2-Chloro-6-(trichloromethyl)-pyridine Nitrapyrin, N-Serve Dow Chemical Co.
5-Ethoxy-3-trichloromethyl-1, 2, 4-thiadiazol Dwell, Terrazole, Etradiazo) Uniroyal Chemical
Dicyandiamide DCD SKW Trostberg AG
3,4-Dimethylpyrazole phosphate DMPP (ENTEC) BASF AG
2-Amino-4-chloro-6-methyl-pyrimidine AM Mitsui Toatsu Co.
2-Mercapto-benzothiazole MBT Onodo Chemical Industries
2-Sulfanilamidothiazole ST Mitsui Toatsu Co.
Thiourea TU Nitto Ryuso
294 Australian Journal of Soil Research D. Chen et al.
Beckwith et al. 1998). The effectiveness of DCD in soil is
controlled by temperature, texture, and moisture content
(Prasad and Power 1995; Irigoyen et al. 2003). With
increasing temperature the inhibiting effect of DCD is
greatly decreased (Bronson et al. 1989a; Irigoyen et al. 2003;
Di and Cameron 2004b). Bronson et al. (1989a) found that the
half-life of DCD in a sandy loam was reduced from 52 to
14 days when the temperature was increased from 88Cto228C,
and Di and Cameron (2004b) observed a greater reduction in a
silt loam.
A relatively new nitrication inhibitor, 3, 4-dimethylpyrazole
phosphate (DMPP), was developed by the German company
BASF AG (BASF 1999; Zerulla et al. 2001). It is generally more
effective and longer lasting than DCD in inhibiting nitrication,
and inhibition was achieved with lower rates of application
(0.51.5 kg DMPP/ha). DMPP has been found to reduce nitrate
and nitrite levels in soil after application of ammonium-based
fertilisers and cattle slurry, leading to signicantly lower nitric
oxide and nitrous oxide emissions, and nitrate leaching, and to
improve crop yields (Dittert et al. 2001; Pasda et al. 2001;
Zerulla et al. 2001; Chao et al. 2005; Menéndez et al. 2006).
Weiske et al. (2001b) showed that DMPP reduced emission of
nitrous oxide by 49% (averaged over 3 years), which was
considerably more than DCD (average reduction 26%).
European eld trials demonstrated that addition of DMPP
increased yields of winter wheat, wetland rice, maize,
potatoes, sugar beets, carrots, lettuce, radish, cauliower, and
onions, allowed lower rates of nitrogen fertiliser, or permitted
fewer applications to be used to attain the same yields as
treatments without DMPP (Pasda et al. 2001).
The effectiveness of DMPP, like DCD, is inuenced by
temperature, soil texture, and moisture (Barth et al. 2001;
Pasda et al. 2001; Merino et al. 2005). Merino et al. (2005)
found that DMPP applied with cattle slurry was able to maintain
soil mineral nitrogen in the ammonium form for 22 days and
reduce nitrous oxide emission by 69% in autumn, but in spring
its effect on soil mineral N lasted for only 714 days, and
reduced nitrous oxide loss by 48%.
Other nitrication inhibitors that have been used successfully
in eld trials include acetylene, substituted acetylenes,
etridiazole, and a natural product from the Neem tree
(Azadirachta melia). Acetylene is a potent inhibitor of
nitrication, but because it is a gas, it is difcult to add and
keep in soil at the correct concentration to inhibit the oxidation of
ammonium. Calcium carbide coated with layers of wax and
shellac has been used to provide a slow-release source of
acetylene to inhibit nitrication (Mosier 1994). This
technique has increased the yield or recovery of nitrogen in
irrigated wheat, maize, cotton, and ooded rice (Bronson and
Mosier 1991; Bronson et al. 1992; Freney et al. 1992a, 1993;
Zhang et al. 1992). Another product, a polyethylene matrix
containing small particles of calcium carbide and various
additives to provide controlled water penetration and
acetylene release, has been developed as an alternative
slow-release source of acetylene. In laboratory studies, this
matrix inhibited nitrication for 90 days and considerably
slowed the oxidation for 180 days (Freney et al. 2000). It
also retarded nitrication in an irrigated corn eld for at least
48 days (Randall et al. 2002). The substituted acetylenes
2-ethynylpyridine and phenylacetylene are very effective
inhibitors of nitrication in the eld (Freney et al. 1993;
Chen et al. 1994, 1998a, 1998b), but their current price
restricts their use by farmers.
Etridiazole (Terrazole, Dwell) was found to be a very
effective nitrication inhibitor in laboratory investigations
(Liu et al. 1984; Raiet al. 1984; McCarty and Bremner
1990), and it has been shown to inhibit nitrication for
prolonged periods in the eld (Somda et al. 1989; Rochester
et al. 1994) and to substantially improve yields for a variety of
eld and horticultural crops (Somda et al. 1990) and irrigated
cotton (Rochester et al. 1994, 1996).
Various products (cake and oil) from the seeds of the Neem
tree have been tested to determine whether they could be used as
cheap nitrication inhibitors for resource-poor Indian farmers
(Majumdar et al. 2000; Malla et al. 2005). Field experiments on
the Indo-Gangetic plain showed that application of neem cake
and neem oil with the fertiliser signicantly reduced the
emission of nitrous oxide. Addition of neem cake also
signicantly increased the yield of rice (Malla et al. 2005).
Unless care is taken to place ammonium-based fertilisers
below the soil surface, use of nitrication inhibitors may result in
increased ammonia volatilisation (Rodgers 1983; Chaiwanakupt
et al. 1996).
Potential for use of enhanced efciency fertilisers
in Australia
Research suggests that the effectiveness of different controlled
release fertilisers, and urease and nitrication inhibitors will
depend upon crop, soil climate, and management factors. The
broadacre agricultural industries in Australia which have been
identied as high nitrogen users are those producing cereals,
sugarcane, cotton, and pasture (Table 1). Some dairy pastures
receive up to 300 kg N/ha.year (Eckard 2004). Horticultural
cropping and turf production are also big users of nitrogen, but
these industries are beyond the scope of this review. Each of
these industries is likely to benet from the use of the enhanced
fertilisation techniques, but the best technique for each crop is
likely to vary.
The major wheat-producing regions are in southern Western
Australia, New South Wales, South Australia, and western
Victoria where the climate is temperate and the soils are
mainly Chromosols, Sodosols, Vertosols, and Calcarasols
(Isbell 1996). The pasture-producing areas that have high
nitrogen inputs are the rainfed or irrigated dairying regions
(Eckard 2004). Most of the dairy pastures are in Victoria,
which is responsible for 64% of Australias milk production
(Dairy Australia 2006), and most of the dairy cattle are in the
Western District (rainfed), Goulburn (irrigated), and Gippsland
(ABS 2005). The main soils in these regions are, respectively,
Chromosols, Sodosols, and Vertosols; Sodosols; and Dermosols
and Ferrosols. The climate in these regions is temperate.
Sugarcane is grown along a 2000-km strip of land on the east
coast of Australia from northern New South Wales to north
Queensland. About one-third of this crop is grown in north
Queensland from Ingham to Mossman. This area has a humid
tropical climate, and sugarcane is grown on soils formed from
alluvial deposits, the deep red and yellow friable loams and the
Improving efciency of fertiliser nitrogen Australian Journal of Soil Research 295
krasnozems (Wood 1991). In the subtropical areas, the crop is
grown on red loams around Bundaberg, and on acid sulfate soils
in the coastal lowland regions. Cotton is grown throughout NSW
and Queensland on alkaline heavy clay soils where the climate
ranges from temperate to subtropical.
Urease inhibitors are expected to be most benecial on
soils where loss of ammonia from application of urea
fertiliser is high. This is likely to be when urea is applied to
the surface of pasture soils (e.g. in the dairy industry) or
other soils which have high urease activity due to lack
of cultivation or the accumulation of organic matter
(e.g. sugarcane trash). Ammonia loss will also occur when
incorporation of urea is difcult and there is little opportunity
for the urea to move into the soil with inltrating water
(e.g. rainfed wheat). Nitrication inhibitors are likely to have
the greatest benet on soils where nitrogen losses due to
leaching or denitrication are large. Leaching losses are more
likely to occur on coarse-textured, free-draining soils under
heavy rainfall (e.g. sugarcane soils in the tropics) than on
ne-textured clay soils with low rainfall (cotton soils in
western NSW). Losses due to denitrication are expected to
be large in warm, ooded, or waterlogged soils (cotton and rice
soils), in soils to which plant residues have been added
(sugarcane and banana soils), and in dung and urine patches
(pasture soils). Benets from the use of controlled release
fertilisers could potentially occur in all the agricultural
industries, as their use should limit losses by all processes.
The choice of controlled release fertiliser, urease inhibitor, or
nitrication inhibitor is likely to be determined more by factors
such as price and availability rather than by degree of
effectiveness, as many of the compounds shown to be very
effective in the laboratory and small-scale trials are not available
commercially. Available products which have the potential to
increase yield, nitrogen use efciency, or loss of nitrogen are
described below.
Controlled release fertilisers
The controlled release fertilisers that appear to show the greatest
potential for dryland and irrigated cropping, and pasture are
(i) a polymer-coated urea (Environmentally Smart Nitrogen;
Agrium 2006); (ii) a polyolen-coated urea (Meister; Chisso
Corporation 2006); and (iii) a humic-acid-coated urea (Black
Urea; Advanced Nutrients Australia 2006).
Environmentally Smart Nitrogen has been extensively used
in the USA and Canada and recently in trials in subtropical
Queensland. It maximised nitrogen use efciency and
minimised nitrogen losses to the environment (Blaylock et al.
2005; Agrium 2006). Meister comes in several forms having
different release types and times. Meister-SS15 shows a
sigmoidal-type release, with a lag period of 70 days and a
release period of 80 days (Shoji et al. 2001). This makes it
ideal for dryland wheat, which requires nitrogen fertilisation
approximately 80 days after sowing to supply nitrogen for
grain-ll. Urea coated with humic acid has signicantly
reduced nitrogen loss and enhanced nitrogen uptake by
dryland wheat in eld trials at Quirindi, NSW, and increased
dryland pasture yields compared with urea (Advanced
Nutrients Australia 2006). Addition of humic acid to urea has
also reduced ammonia loss from acid soils (Garcia Serna et al.
1996; Siva et al. 2000).
Urease inhibitors
The most readily available compound, N-(n-butyl)
thiophosphoric triamide, is sold in Australia as Agrotain,
which contains 2025% active ingredient (IMC-Agrico 1997).
Agrotain is marketed by Incitec Pivot Ltd in the following
formulations: (i) Green Urea 14, which contains 45.8%
nitrogen as urea and Agrotain @ 5.0 L/t to reduce the loss of
ammonia by volatilisation for up to 14 days; and (ii) Green Urea
7, which contains 45.9% nitrogen and Agrotain @ 3.0 L/t to
reduce ammonia volatilisation for up to 7 days (Incitec Pivot Ltd
2006).
Nitrication inhibitors
The products which show the greatest potential for reducing
nitrogen loss from agricultural industries in Australia are (i)
DMPP (rainfed wheat and pasture), (ii) DCD (rainfed and
irrigated pasture, wheat), and (iii) etridiazole (irrigated
cotton). DMPP seems to be the best product because of its
positive effects on yield and nitrogen loss at low concentrations,
and because of its stability and lack of movement in soil. It may
need to be applied at slightly higher concentrations in warm
conditions. It is marketed as ENTEC by BASF and is distributed
by Incitec-Pivot in Australia (Incitec Pivot Ltd 2006). DCD
(marketed as Didin by SKW Trotsberg, Germany) needs to be
applied at higher rates than DMPP. It is unstable at high
temperatures, and thus is likely to be more effective when
used during winter and autumn.
Further testing of these materials under a range of conditions
is required to select the best material for a particular industry in
Australia, and to determine the economics of its use.
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Manuscript received 27 November 2007, accepted 19 March 2008
Improving efciency of fertiliser nitrogen Australian Journal of Soil Research 301
http://www.publish.csiro.au/journals/ajsr
... Table 1 is a summary of the reviews. Among the 26 works, seven of them targetted urea or nitrogenous fertilisers [13,14,[45][46][47][48][49]. Only 9 patents were introduced in the seven reviews, indicating that the research knowledge in patents has been massively undervalued since the starting age of the research. ...
... included in this physically controlled category. In the first type nutrients are coated in a water-insoluble or semi-permeable coating while in the other type the nutrient particles are uniformly dispersed through a protective matrix [46,49,72]. Urea as one of the most popular fertilisers is widely included in this category [73][74][75][76][77][78][79][80][81][82]. ...
... Another popular method classifies fertilisers according to the material types used in manufacturing process. Some research works classify the fertilisers into 1) organic low solubility compounds; 2) fertilisers with physical barriers; and 3) inorganic low solubility compounds [40,46,49,71]. Organic low solubility compounds can be further classified into biologically decomposing compounds comprising urea formaldehyde and chemically decomposing compounds such as IBDU [40,71]. ...
Article
Fertiliser has been a vital part of agriculture due to it boosting crop productivity and preventing starvation throughout the world. Despite this huge contribution, the application of nitrogen (N) fertilisers results in N leaching and the formation of greenhouse gases, which threaten the environment and human health. To minimise the impacts, slow/controlled release fertilisers (S/CRFs) have been being developed since the beginning of the 20th century. Despite the efforts made over a century, the basic terminological and classification information of these fertilisers remains vague. The scientific knowledge published in S/CRF patents has also been overlooked since the beginning. This review focused on the information gaps, clarified the definitions, differentiation and classification methods that have been randomly used in previous literature. The objectives, formulations and technologies of 109 controlled release urea patents involving sulphur coated urea, polymer coated urea and urea matrix fertilisers published in the years since these products emerged were also reviewed to 1) highlight the overlooked scientific knowledge in the patents; 2) understand the evolutionary processes and current research states of the products; 3) clarify research preferences and challenges to date; 4) identify remaining gaps for the future direction. It is expected that the organised basic information and the patent knowledge highlighted in this paper can be new resources and foster the development of S/CRFs in the future.
... In this study, increased NUE (expressed as PFP N and AE N ) in maize and rice indicates that the use of both PCU and UB can reduce a significant amount of N losses from plant-soil system to the environment, which is corroborated with several previous studies (Geng et al. 2016;Agyin-Birikorang et al. 2018;Adu-Gyamfi et al. 2019;Baral, Pande, Gaihre, et al. 2020;Chen et al. 2020). Generally, NUE of granular urea is 20-35% (Naz and Sulaiman 2016), which can be reduced further drastically with poor fertilizer management practices resulting up to 92% N lost from the system mainly through leaching, volatilization, nitrification/denitrification and runoff (Chen et al. 2008). A higher amount of N losses from the soil-plant system can have a negative impact on environment such as groundwater contamination and downstream water pollution and tropospheric pollution (N 2 O emissions) contributing to global warming and climate change (Zhang et al. 2015;Wang et al. 2020). ...
... An important strategy in this context has been the use of nitrification inhibitors (NIs). These are the chemical compounds that have the potential to delay bacterial oxidation of ammonium by depressing the activities of soil-nitrifying bacteria to reduce N 2 O emissions (Chen et al. 2008;de Klein and Eckard 2008), but they can stimulate ammonia volatilization . Several compounds have been proposed and patented as NIs, such as S. benzylisothiouronium (SBT) butanoate and SBT fluroate, to enhance crop yield and reduce N 2 O emissions (Bhatia et al. 2010). ...
Article
Nitrogen pollution in the environment has become a global concern. Being multidimensional and complex, nitrogen pollution requires a comprehensive package of efforts for its effective management. This article reviews the existing technologies for the treatment and management of nitrogen pollution, water soluble or gaseous, originating from wastewater and agriculture. In the wastewater section, technologies for the wastewater treatment as well as the recovery of nitrogen are reviewed, including physico-chemical and biological techniques. Hybrid treatments could combine the strengths of these strategies to enhance nitrogen removal in wastewater. Moreover, the use of solid wastes to develop efficient adsorbents for nitrogen recovery from wastewater and their subsequent valorization in agricultural soils can be highly rewarding. The agriculture-associated nitrogen pollution can be addressed by the effective management of nitrogenous fertilizers, soils, and crops and the adoption of conservation agriculture practices. It is crucial to improve nitrogen use efficiency in crop production to tackle the challenges of climate change, food security, and environmental degradation. The breeding of crop genotypes possessing an improved nitrogen efficiency and engineering the legume symbiosis can be quite helpful for this. Future research directions have been recognized to foster the research into sustainable management of nitrogen. Collaborative efforts and a comprehensive understanding of existing knowledge of these techniques are required to upscale these techniques for field-scale applications. By presenting a detailed overview of strategies for nitrogen treatment and management in wastewater and agriculture, this article intends to enable a better understanding on this theme.
... Some studies show that only between 7-22% of P fertiliser is utilised by dryland crops (McBeath et al. 2012) and on average ~40% of applied N is recovered by the crop in the year of application (Angus and Grace 2017) but this can range from 10-70% depending on seasonal conditions (Wallace et al. 2021). There has been considerable research into the development of enhanced efficiency fertilisers to reduce losses of N via denitrification and volatilisation (Chen et al. 2008) and P via chemical fixation/precipitation (Bertrand et al. 2006). However, their relative high cost has precluded commercial use in dryland cropping systems. ...
Chapter
The sensitivity of global food production to frequent weather anomalies (e.g., flooding, soil waterlogging, and drought) has emerged as a threat amid climate change. Among abiotic stresses, flooding is the most damaging stress, affecting 10-16% of agricultural lands worldwide. Flooding alone caused around two-thirds of the total crop losses between 2006-2016 and is predicted to increase considerably in the future. In this chapter, “flooding” refers to the condition where the whole plant or plant parts are submerged underwater, and “soil waterlogging” refers to the condition of complete soil pore saturation with moisture. In addition to direct crop damages, flooding and waterlogging also results in several environmental concerns, such as declines in surface and groundwater quality. It is, therefore, critical to manage flooding and soil waterlogging to mitigate adverse impacts on crop production systems by understanding the causes, impacts, and management strategies. Soil waterlogging or flooding can be caused and influenced by increased precipitation frequency, precipitation after irrigation, over-irrigation, soil compaction, shallow water tables, poorly drained soils, and land topography. Soil waterlogging or flooding stresses crops mainly through reduced oxygen levels near the rhizosphere, altered soil physicochemical properties, and reduced nitrogen uptake. Management for soil waterlogging or flooding requires a complementarily integrated approach of agronomic management, genetic improvements, and engineering measures. Major soil management for waterlogging or flooding includes raised bed farming, nutrient management, drainage systems, and controlled farm traffic. The most used crop management techniques for waterlogging management are flood-tolerant varieties, cover crops, altering planting dates, and application of plant growth regulators. Despite the development of several management strategies, there is enormous scope for research to develop more flood-resistant varieties, integrate various precision agricultural techniques, and utilise remote sensing and crop modelling for mitigating waterlogging stress and losses in agricultural production systems. https://books.google.com/books?hl=en&lr=&id=qpiDEAAAQBAJ&oi=fnd&pg=PA62&dq=info:3Y2-ETjP0PcJ:scholar.google.com&ots=Cy5gdtMssp&sig=qc1ejTsrono6PhHpM43bZ0_8tMo
... Some studies show that only between 7-22% of P fertiliser is utilised by dryland crops (McBeath et al. 2012) and on average ~40% of applied N is recovered by the crop in the year of application (Angus and Grace 2017) but this can range from 10-70% depending on seasonal conditions (Wallace et al. 2021). There has been considerable research into the development of enhanced efficiency fertilisers to reduce losses of N via denitrification and volatilisation (Chen et al. 2008) and P via chemical fixation/precipitation (Bertrand et al. 2006). However, their relative high cost has precluded commercial use in dryland cropping systems. ...
Chapter
The agricultural practices introduced by European colonisers have been practiced in South America for many years, resulting in depletion of the soil’s natural fertility. The introduction of fertilisers and acidity amendments occurred in the mid-1960s and boosted production of many areas, but still with high soil erosion and low levels of organic matter. The widespread use of conservation systems, such as no-tillage, occurred latter and changed the relationship between soil indices and crop responses. Nowadays, South America represents 47% of the total global area under no-tillage, which covers an area around 56 million hectares. No-tillage reduces the annual rate of decomposition and increases the mean residence time of the soil organic matter. One of the great challenges in different countries nowadays, in the most diverse cropping systems, is to increase biodiversity through the proper use of different species of cover crops, mainly mixed cover crops, in order to improve the microbiota, achieve better soil-plant equilibrium and contribute strongly to enhance the soil organic carbon (C) sequestration. In some countries, the challenge of no-tillage adoption is getting closer to being overcome. The current challenge is working on a cropping system with diversified species and high residue input. The adoption of legume cover crops as a source of nitrogen (N) seems to be very important, resulting in higher accumulation of soil organic matter compared to N fertilisation. The management of soil acidity was, and continues to be, one of the main factors limiting crop yields. The problems of diagnosis are mainly related to the sampled soil layer and the indicators used for decision making. Recent studies have demonstrated that neither the 0-10 cm nor the 0-20 cm soil layer is suitable for diagnosing soil acidity and the potential crop yield in no-tillage systems with chemical restrictions in the subsurface. In these areas, a stratified soil analysis is essential, covering at least one subsurface layer (10-20 cm). The incorporation of limestone may be the best and fastest way to eliminate problems related to soil acidity in the subsurface. Significant increases in crop yields have been observed when using agricultural gypsum based on the diagnostic soil layer of 20-40 cm. Doses between 2 and 3 Mg ha-1 are sufficient to obtain 95% of the maximum crop yield. For phosphorus (P), there is no doubt that the biggest problem is restricted access: by farmers at the micro scale and by countries at the macro scale. When accessible, the inappropriate use of P fertilisers is often noticed. The correct approach would be to raise the available P content above the critical level in the 0-20 cm soil layer, and then reapply the amount exported by crops in the row at sowing time. Regarding potassium (K), although there is an assumption that the tropical soils found in South America have only minerals such as kaolinite and oxides, there are several studies that show that the mineralogy of these soils is not so uniform. It is common to observe situations where 2:1 clay minerals are present and crops do not respond to the addition of K fertiliser, or the available K content does not increase over time. The research on sulfur (S) has advanced and shown that in tropical soils there is a higher positive crop response to S addition than in subtropical soils, regardless of available soil S contents. The evaluation of the 20-40 cm soil layer can support decision making regarding S management. To enhance production of plants and to increase the soil organic matter content, it is necessary to encourage and promote the horizontal and vertical monitoring of soil fertility. Associated with this, it is necessary to establish research networks aimed at improving the establishment of critical levels of soil acidity and available nutrients in the soil to guide decision-making more assertively, thus maximising productivity and promoting more sustainable production.
Article
Enhanced-efficiency nitrogen fertilizers provide an opportunity for sustainable intensification of agricultural industries. However, field experiments evaluating yield and nitrogen loss benefits from enhanced-efficiency fertilizers often fail to obtain statistically significant treatment differences. Agricultural systems modeling provides a means to perform thousands of virtual response trials, allowing us to unravel the complex interactions between crop, management, and seasonal climate that determine the efficacy of these fertilizers. Here, we present simulations of controlled-release fertilizer use in Australian sugarcane (Saccharum sp. L.) production in a wet tropical climate. To quantify the agronomic and environmental benefits, we analyze the yield and nitrogen loss responses to nitrogen rate (response curves), comparing those for urea and controlled-release fertilizers. We also evaluate the impacts of soil type, crop start times, and controlled-release patterns as they interact with seasonal climate and rainfall distribution. The simulation results showed that nitrogen loss and yield benefits were highly variable, and their likelihood determined by three prerequisite conditions: (1) sufficient longevity of protection of the fertilizer nitrogen, (2) occurrence of a nitrogen loss event during this period of protection and before the nitrogen is taken up by the crop, and (3) the crop being responsive to the fertilizer nitrogen. These prerequisite conditions extend to other cropping systems as well as to other enhanced-efficiency nitrogen fertilizers such as nitrification inhibitors. Here, for the first time, we provide a framework for understanding the inconsistent results in field experiments testing the efficacy of enhanced-efficiency nitrogen fertilizers. This understanding will help improve the setting, design, and interpretation of experiments for better demonstration of benefits as well as identify where enhanced-efficiency fertilizers can best increase sustainability of nitrogen management.
Article
Previously, we reported that the content of total oxalic acid of spinach in the solution culture decreased along with increasing ratios of NH_4-N to NO_3-N in the solution. In the present field study, we attempted to decrease the content of oxalic acid of spinach by growing with slow-releasing fertilizers, since we could expect the absorption of NH_4-N by spinach just after being released from these fertilizers. Three cultivars of spinach were grown in an Ando soil with ammonium sulfate(AS), coated urea(CU)and coated ammonium phosphate(CAP), at 15 g N m^<-2>. The seeds were sown on the top of the row and the fertilizers were applied 6 cm below the seeds with 10 cm width. NH_4-N and NO_3-N in the soil block which contained the fertilizers were extracted with a 100 g L^<-1> KCl solution and measured colorimetrically. The NH_4-N contents 22 d after fertilizing were 1.9mg/100 g dry soil in the AS plot, but they were 10.0 and 16.3 mg/100 g dry soil in the CU and CAP plots, respectively, and a significant content of NH_4-N(16.1 mg/100 g dry soil)was detected only in the CAP at harvest. It was thought that a part of these NH_4-N were absorbed by spinach before nitrification. The contents of oxalic acid in the CU and CAP plots, compared with those in the AS plot, were remarkably decreased in spinach applied with CAP(47-72% of the value found in the AS plot). Nitrate was further decreased and sugar was increased in the both CU and CAP plots in two cultivars, and total ascorbic acid was increased in the CU plot in three cultivars. So application of slow-releasing nitrogen fertilizers induced a desirable effect on the quality of spinach.
Article
This book presents an interdisciplinary approach for agriculture, hydrology and water quality to work towards an improved understanding of the processes involved and impacts of agriculture on water. This consists 22 chapters divided into 3 sections: (1) agriculture as a potential source of water pollution viz., nitrogen, phosphorus, manures, pesticides and persistent organic pollutants, heavy metals, human enteric pathogens, sediment and nutrient balances; (2) hydrology as the transport of water pollution; and (3) impacts and case studies from around the world.
Article
Experiments in our laboratory showed that phenylphosporo diamidate (PPD), N-(n-butyl) thiophosphoric triamide (NBTE'T) and cyclohexylphosphoric triamide (CHPT) inhibited soil urease activity. The effects of the inhibitors on dry matter production and urea-N uptake by wheat plants grown in pots in a glasshouse (23C day temperature, no wind) were studied. Under conditions that minimised ammonia loss from the soil surface, urease inhibitors applied at 0.5 - 1.0% of the urea application rate did not influence plant dry matter or N uptake. Recovery of 15N from the soil-plant systems was less at the higher rate of 15N-urea (200 mg urea-N per pot), as compared with a lower rate (50 mg urea-N per pot).
Article
Ammonia (NH3) volatilization is a major pathway of N loss which limits the efficiency of urea as a fertilizer when surface-applied to soils. High pH and low cation exchange capacity in soils have been identified as the principal causes of NH3 volatilization from urea. An attempt was made to establish a preferred environment within the urea-soil reaction zone (microsite) using humic substances derived from palm oil mill effluent (POME) and peat. Both POME and peat are rich in organic matter, and contain humic substances across their respective organic matrices. Humic substances have been shown to interact with ammoniacal compounds and urea. Derived humic substances were separately matrixed with urea into pelletised form and evaluated under laboratory regimes for per cent NH3 volatilization, pH change, and NH4+-N recovery. The results showed that the effects of humic substances, particularly humic acid, on reducing NH3 volatilization was more pronounced in the acid soil. However, such a reduction was not accompanied by a corresponding increase in ammonium ion (NH4+) recovery. The ability of humic substances to reduce NH3 volatilization from urea could be attributed to other mechanisms, i.e., urease inhibition, urea absorption, and NH3 fixation which possibly operated simultaneously.