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Fertilizer Use Efficiency and Nitrate Leaching in a Tropical Sandy Soil

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  • Marondera University of Agricultural Sciences and Technology

Abstract and Figures

Maize (Zea mays L.) production in the smallholder farming areas of Zimbabwe is based on both organic and mineral nutrient sources. A study was conducted to determine the effect of composted cattle manure, mineral N fertilizer, and their combinations on NO3 concentrations in leachate leaving the root zone and to establish N fertilization rates that minimize leaching. Maize was grown for three seasons (1996-1997, 1997-1998, and 1998-1999) in field lysimeters repacked with a coarse-grained sandy soil (Typic Kandiustalf). Leachate volumes ranged from 480 to 509 mm yr(-1) (1395 mm rainfall) in 1996-1997, 296 to 335 mm yr(-1) (840 mm rainfall) in 1997-1998, and 606 to 635 mm yr(-1) (1387 mm rainfall) in 1998-1999. Mineral N fertilizer, especially the high rate (120 kg N ha(-1)), and manure plus mineral N fertilizer combinations resulted in high NO3 leachate concentrations (up to 34 mg N L(-1)) and NO3 losses (up to 56 kg N ha(-1) yr(-1)) in 1996-1997, which represent both environmental and economic concerns. Although the leaching losses were relatively small in the other seasons, they are still of great significance in African smallholder farming where fertilizer is unaffordable for most farmers. Nitrate leaching from sole manure treatments was relatively low (average of less than 20 kg N ha(-1) yr(-1)), whereas the crop uptake efficiency of mineral N fertilizer was enhanced by up to 26% when manure and mineral N fertilizer were applied in combination. The low manure (12.5 Mg ha(-1)) plus 60 kg N ha(-1) fertilizer treatment was best in terms of maintaining dry matter yield and minimizing N leaching losses.
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Plant and Environment Interactions
Fertilizer Use Efficiency and Nitrate Leaching in a Tropical Sandy Soil
J. Nyamangara,* L. F. Bergstro
¨
m, M. I. Piha, and K. E. Giller
ABSTRACT
fields (homefields) resulting in high application rates
(up to 80 Mg ha
1
, or 800 kg N ha
1
) (Mugwira and
Maize (Zea mays L.) production in the smallholder farming areas
Murwira, 1998). The high manure application rates im-
of Zimbabwe is based on both organic and mineral nutrient sources.
A study was conducted to determine the effect of composted cattle ply that the total N loading is much greater than crop
manure, mineral N fertilizer, and their combinations on NO
3
concen-
requirement, and depending on the N mineralization
trations in leachate leaving the root zone and to establish N fertiliza-
pattern from the manure, excessive N availability may
tion rates that minimize leaching. Maize was grown for three seasons
occur. Coupled with high-intensity rain storms charac-
(1996–1997, 1997–1998, and 1998–1999) in field lysimeters repacked
teristic of tropical and subtropical regions, NO
3
leaching
with a coarse-grained sandy soil (Typic Kandiustalf). Leachate vol-
potential in fields amended with high rates of manure
umes ranged from 480 to 509 mm yr
1
(1395 mm rainfall) in 1996–1997,
may be high.
296 to 335 mm yr
1
(840 mm rainfall) in 1997–1998, and 606 to 635 mm
The Alvord system, recommended for the small-
yr
1
(1387 mm rainfall) in 1998–1999. Mineral N fertilizer, especially
holder farming sector of Zimbabwe, has widely been
the high rate (120 kg N ha
1
), and manure plus mineral N fertilizer com-
adopted by the farmers and is based on the application
binations resulted in high NO
3
leachate concentrations (up to 34 mg
NL
1
) and NO
3
losses (up to 56 kg N ha
1
yr
1
) in 1996–1997, which of about 40 Mg ha
1
of manure (248–488 kg N ha
1
)
represent both environmental and economic concerns. Although the
(Mugwira and Mukurumbira, 1986; Mugwira and Mur-
leaching losses were relatively small in the other seasons, they are still
wira, 1998) to a four-course rotation of two maize crops,
of great significance in African smallholder farming where fertilizer is
followed by a legume and finally a small grain crop
unaffordable for most farmers. Nitrate leaching from sole manure
(Grant, 1976). The system was developed in the 1940s
treatments was relatively low (average of less than 20 kg N ha
1
yr
1
),
by D.E. Alvord, a missionary who conducted extensive
whereas the crop uptake efficiency of mineral N fertilizer was en-
field trials on sandy soils in the semi-arid zones of
hanced by up to 26% when manure and mineral N fertilizer were
Zimbabwe. However, the initial immobilization of N
applied in combination. The low manure (12.5 Mg ha
1
) plus 60 kg
by manures from smallholder farming areas (Muller-
Nha
1
fertilizer treatment was best in terms of maintaining dry matter
Sa
¨
mann and Kotschi, 1994; Murwira and Kirchmann,
yield and minimizing N leaching losses.
1993) has prompted farmers to supplement the manures
with inorganic N fertilizer. There is a need to improve
the timing of inorganic N fertilizer application when it
T
he smallholder cropping systems in much of
is applied in combination with manure to increase N
southern and eastern Africa are based on maize,
uptake, and minimize N leaching losses.
the staple food crop. In the cropping systems in Malawi,
Most studies on N leaching from soils amended with
Zambia, and Zimbabwe, maize accounts for about 60%
manure and/or inorganic fertilizers have focused on hu-
of the cropped area (Kumwenda et al., 1996). Cattle ma-
mid temperate regions (Beckwith et al., 1998; Thomsen
nure remains the major source of nutrients for plant
et al., 1993; Unwin, 1986), and overall, few quantitative
growth in the smallholder farming sector of Zimbabwe.
measurements of N leaching have been made in tropical
Although some mineral fertilizers are used, the rela-
and subtropical regions of Africa (Arora and Juo, 1982;
tively high prices of fertilizers and poor accessibility of
Omoti et al., 1983; Wong et al., 1987). In Zimbabwe, N
supply limit the amount of fertilizer that the smallholder
leaching losses of up to 39 kg N ha
1
yr
1
have been
farmers apply to their crops. For example, in the 1989–
reported on a sandy soil (Kamukondiwa and Bergstro
¨
m,
1990 growing season, smallholder farmers applied NPKS
1994a). However, that study was performed during a
fertilizer at an average rate of 53 kg ha
1
compared
sequence of dry years, which limits the representative-
with 705 kg ha
1
by large-scale commercial farmers in
ness of the results. Other studies, also on sandy soils in
Zimbabwe (Humphreys, 1991). Although cattle manure
Zimbabwe (Hagmann, 1994; Vogel et al., 1994), indi-
is generally inadequate and of low N (1%) content
cated that most of the fertilizer (up to 54% of applied
(Mugwira and Mukurumbira, 1986), farmers tend to
N) was leached out of the top 0.5 m of soil when heavy
apply large amounts of the manure to certain preferred
rains followed N fertilizer application. However, under
such conditions some of the leached nitrogen can proba-
J. Nyamangara, M.I. Piha, and K.E. Giller, Dep. of Soil Science and
bly be recovered by roots later in the season.
Agricultural Engineering, Univ. of Zimbabwe, P.O. Box MP167,
Although rainfall is seasonal, highly variable, and gen-
Mount Pleasant, Harare, Zimbabwe. L.F. Bergstro
¨
m, Division of Wa-
ter Quality Management, Dep. of Soil Sciences, Swedish Univ. of erally insufficient in most smallholder farming areas of
Agricultural Sciences, P.O. Box 7072, S-750 07 Uppsala, Sweden.
Zimbabwe (Piha, 1993), its high intensity (up to 250 mm
Received 12 Nov. 2001. *Corresponding author (jnyamangara@agric.
h
1
) coupled with the predominantly coarse-textured
uz.ac.zw).
Abbreviations: NDFF, nitrogen derived from fertilizer.Published in J. Environ. Qual. 32:599–606 (2003).
599
600 J. ENVIRON. QUAL., VOL. 32, MARCH–APRIL 2003
nitrogen behavior in coarse-textured soils (Bergstro
¨
m, 1990).
soils used for agriculture (Twomlow, 1994) may trigger
Before the experiment was started in the summer of 1996, the
N leaching. Given also the relatively high cost of fertil-
lysimeters were water saturated from the bottom end and
izer compared with produce, efficient use of N fertilizer
thereafter allowed to drain freely, and left to settle for 14 mo.
is of both agroeconomic and environmental importance.
This led us to design a study in which the objective
Experimental Treatments
was to measure NO
3
in water leaving the root zone in
The treatments were beef cattle manure (0, 12.5, and 37.5
agricultural fields typical of smallholder cropping sys-
Mg ha
1
, which contained 0, 116, and 348 kg N ha
1
, respec-
tems of Zimbabwe, and to establish fertilization rates
tively) and N fertilizer (0, 60, and 120 kg N ha
1
as
15
NH
4
15
N0
3
)
that minimize N leaching losses while maintaining crop
replicated three times in a two-factor randomized complete
yields.
block design. The fertilizer
15
N (derived from Amersham UK
Ltd.) enrichment was 3.3% atom excess (AE) (0.3776 atom
MATERIALS AND METHODS
% background enrichment) in the first season and 9.0% AE
in the second season. No fertilizer was added in the third
Experimental Location and Soil Properties
season. All the fertilizer was applied at planting. The N fertil-
The 3-yr study was conducted at Domboshawa Training
izer was dissolved in water and applied uniformly in the lysime-
Centre (1735 S, 3110 E), about 35 km north of Harare,
ters after removing the top-5-cm soil layer, and the soil was
Zimbabwe, where average rainfall is 900 mm yr
1
and mostly
replaced soon after fertilizer application. It was assumed that
restricted to the summer season (November–April). Average
the effect of residual
15
N fertilizer was minimal in the second
annual temperature is 18.8C, with the highest and lowest
season given the much higher enrichment that was used in
monthly mean temperatures being 29C (October) and 6.5C
the second season.
(July), respectively. The soil was a Typic Kandiustalf derived
The manure was aerobically composted (i.e., manure dug
from granitic parent material with relatively low water holding
out of a cattle pen and heaped in the open for 3 mo) and
capacity (9% available water capacity) (Vogel et al., 1994).
was collected from the Mhondoro smallholder farming area,
The soil consisted of a coarse loamy sand topsoil (0–0.3 m)
approximately 70 km southwest of Harare. In Zimbabwe cattle
overlying a sandy loam upper subsoil (0.3–0.6 m) and a clay
manure is aerobically composted for 3 to 4 mo in pits that
loam lower subsoil (0.6–0.1.0 m) (Table 1). The experimental
are covered with soil on the surface. The manure contained
site had lain fallow for at least six years before the experiment.
8.4% C and 0.93% N (C to N ratio 9) on a dry matter
Domboshawa Training Centre lies in a region classified as
basis, but after correction for inorganic material the C and N
high potential in terms of crop production in Zimbabwe.
contents were 41.9 and 4.64%, respectively (Nyamangara et
al., 1999). Most of the inorganic material is soil ingested by
grazing animals or mixed in as a result of trampling of the
Lysimeter Installations
manure in the cattle pen (Mugwira and Murwira, 1998). The
A lysimeter station consisting of 27 repacked and gravity-
manure rates were based on current recommendations for
drained lysimeters was built in the autumn of 1995 at the field
maize in smallholder farming areas of Zimbabwe where about
site. A trench at the center of the lysimeter station contained
35 to 40 Mg ha
1
is applied every fourth year, or annually at
27 buckets to collect leachate. The lysimeters, square-shaped
about 12 Mg ha
1
(Mugwira and Murwira, 1998). The 12.5
with a surface area of 1 m
2
and a depth of 1.1 m, were con-
Mg ha
1
manure and N fertilizer treatments were applied
structed from 1.6-mm-thick galvanized steel sheets. The lysim-
every year but the larger manure treatment was applied only
eter walls were painted with an oil-based paint to provide
in the first year. The same manure was used to ensure the
a rough surface that would prevent water from channeling
same composition. Annual basal applications of 30 kg K ha
1
between the soil and the inside tank walls. The lysimeter boxes
as potassium chloride, 30 kg P ha
1
, and 30 kg S ha
1
as single
were surrounded by field soil to prevent excessive heating of
super phosphate were made to all treatments. The manure
the lysimeter soil.
and fertilizer, all applied before planting, were incorporated
A 1-mm wire mesh was fixed at the lysimeter outlet and
into the top 5 cm of the soil at planting. Two maize plants
covered with a 10-cm layer of gravel before the soil was re-
were grown in each lysimeter during the rainy summer seasons,
placed, reducing the effective depth of the lysimeters to 1 m.
which were sown on 3 Dec. 1996, 24 Nov. 1997, and 23 Nov.
The gravel improved drainage (Stevens et al., 1992) and also
1998, respectively.
prevented the fine soil material from washing into the 10-mm
steel outflow pipes. The pipes were laid at a slope of approxi-
Sampling and Analytical Procedures
mately 2% to ensure rapid water flow to the collecting vessels.
The soil layers were repacked to original density following The aboveground maize parts were harvested after 12
weeks each year (milk dough stage) and dry matter yield wasthe sequence of the soil profiles identified during site charac-
terization. Repacking the soil was considered appropriate be- determined by oven-drying at 65C. The plant samples were
ground to pass through a 2-mm sieve. Total N content wascause it only introduces small changes in water transport and
Table 1. Selected properties of the experimental soil.
Soil texture†
Soil layer (sand, silt, clay) Organic C Total N C to N ratio CEC‡ pH Bulk density
cm % cmol
c
kg
1
gcm
3
0–10 93, 3, 5 0.40 0.030 13.3 2.7 4.7 1.625
10–27 91, 3, 6 0.17 0.015 11.1 1.2 4.6 1.620
27–40 87, 3, 10 0.13 0.012 10.9 1.4 4.5 1.650
40–70 79, 3, 18 0.13 0.013 9.8 1.6 4.6 1.678
70–130 68, 2, 30 0.08 0.009 9.2 1.7 4.7 1.709
† According to the International Soil Science Society soil classification system (sand, 20–2000 m; silt, 2–20 m; clay, 2 m).
‡ Cation exchange capacity.
NYAMANGARA ET AL.: FERTILIZER USE AND N LEACHING IN A TROPICAL SOIL 601
determined with the semi-micro Kjeldahl method (Bremner CO
2
before being directed to the MS. Signals from a triple
collector detector are integrated by a computer linked to the
and Mulvaney, 1982). In preparation for
15
N analysis, subsam-
MS and results are given as
15
N atom % and total N. The
ples of plant material were ball-milled after grinding to obtain
fraction of N in the plant samples derived from the
15
N-labeled
homogeneous samples. Microsamples (2–6 mg) of this material
fertilizer (NDFF) was calculated by the equation:
were weighed into aluminium foil capsules, which were intro-
duced into a mass-spectrometer (MS) system (Tracer 15N/
NDFF (%
15
N atom excess in plant material)/
(%
15
N atom excess in fertilizer)
[1]
13C; Europa Scientific, Crewe, UK) for
15
N determination.
The system uses a software-controlled Dumas method to pro-
duce molecular N, which is successively scrubbed of water and The value of natural abundance was determined from sam-
Fig. 1. Accumulated leachate in replicated lysimeters of selected treatments, and weekly rainfall and pan evaporation at the experimental site
during the study period.
602 J. ENVIRON. QUAL., VOL. 32, MARCH–APRIL 2003
Table 2. Effects of manure and N fertilizer application on total
ples from nonfertilized areas at the site where the lysimeter
N uptake in maize aboveground plant parts during 1996–1997,
soil was collected.
1997–1998, and 1998–1999 cropping seasons.
Leachate volumes were recorded following each rain event
when breakthrough of leachate occurred. Representative sam-
Total N uptake
ples were taken one to three times each week depending on
N fertilizer application (kg N ha
1
)
volume of leachate for colorimetric NO
3
–N determination by
Manure 0 60 120
the Cd-reduction method analysis (Keeney and Nelson, 1982).
Total NO
3
–N loads were calculated by multiplying the total
Mg ha
1
kgNha
1
NO
3
–N concentration by the volume of leachate. It was as-
1996–1997
sumed that the concentration of NH
4
–N in leachate was neg-
0 25.5 45.4 95.2
ligible.
12.5 48.7 77.9 153.6
37.5 70.8 90.2 189.1
The analysis of variance (ANOVA) procedure was used to
LSD (P 0.05) 19.5
test the effect of manure and mineral fertilizer treatments on
1997–1998
N uptake, NO
3
–N leaching, and leachate volume with the
0 22.5 56.3 63.4
MSTAT statistical package (MSTAT, 1988).
12.5 78.1 105.0 133.6
37.5 96.6 116.0 144.7
LSD (P 0.05) 13.2
RESULTS AND DISCUSSION
1998–1999†
0 4.5 9.8 13.4
Weather and Drainage Conditions
12.5 15.7 21.0 27.0
37.5 18.5 22.5 28.9
The 1996–1997 and 1998–1999 cropping seasons (No-
LSD (P 0.05) 9.0
vember–April) were wetter (1395 and 1387 mm, respec-
† No fertilizer applied in 1998–1999.
tively) than the long-term seasonal average (900 mm)
for the area, whereas in 1997–1998 seasonal rainfall
(840 mm) was close to average. Weekly values of rainfall
but it was not significant (P 0.361) in the third (1998–
are shown in Fig. 1. The highest rainfall intensity was
1999) season. The interaction between the manure and
recorded in 1996–1997 (up to 120 mm d
1
). Accumu-
N fertilizer was mainly additive, that is, the two N
lated leachate volumes accounted for 48 to 51% (480–
sources acted independently of each other in increasing
509 mm) of rainfall recorded up until harvesting in 1996–
N uptake by maize. A synergistic interaction in increas-
1997, 45 to 51% (296–335 mm) in 1997–1998, but was
ing N uptake was only observed in 1996–1997 when
much higher (84–88% or 606–635 mm) in 1998–1999.
combined application of 120 kg N ha
1
fertilizer and
The much higher proportion of accumulated leachate
manure (12.5 and 37.5 Mg ha
1
) resulted in higher N
volume in 1998–1999 (Fig. 1) was mainly attributed to
uptake (6.7 and 13.9%, respectively) compared with the
poor maize growth, which was caused by a severe gray
sum of the separate applications of the manure and N
leaf spot (Cercospora zeae-maydis) infestation that led
fertilizer. In a related field study at the same site, a
to reduced evapotranspiration. Weekly evaporation
significant (P 0.05) and positive manure N fertilizer
rates, which are routinely measured at the study site,
interaction, which was additive, was only observed in
were small compared with weekly rainfall during the
the first season (Nyamangara, 2001).
study period (Fig. 1) and the crop was therefore not
Nitrogen uptake from the manure-only applications
affected by moisture stress in either cropping season.
(12.5 and 37.5 Mg ha
1
) was greater (60 and 36%, re-
There were only small differences in the amounts of
spectively) in the second season compared with the first
leachate between the different treatments, which were
season. This implied that manure N became more avail-
not significant (P 0.05). These differences were of the
able (through mineralization) for plant uptake in the
same magnitude as was found between replicate lysime-
second year compared with the first year. Similar results
ters of the same treatment (Fig. 1). Similar trends have
have been reported in field studies in Zimbabwe for
also been reported both locally (Kamukondiwa and
similar poor-quality manures (Murwira and Kirchmann,
Bergstro
¨
m, 1994a) and under cold temperate conditions
1993; Mugwira, 1984) and elsewhere (Jokela, 1992). By
(Bergstro
¨
m and Kirchmann, 1999).
contrast, N from anaerobically stored manures becomes
available for plant uptake soon after application to
soil (Beckwith et al., 1998; Bergstro
¨
m and Kirchmann,
Aboveground Nitrogen Uptake
1999). Average net uptake of manure N ranged from
Total aboveground N uptake by maize from lysime-
26% in the 12.5 Mg ha
1
and 12.5 Mg ha
1
plus 60 kg
ters that received manure was significantly (P 0.05)
Nha
1
treatments to 55% in the 37.5 Mg ha
1
plus 120
greater than that from the control in all three seasons
kg N ha
1
treatment over the three cropping seasons,
(Table 2). In the N fertilizer treatments, total above-
and for each treatment was highest in the second sea-
ground N uptake was significantly higher than the con-
son (Table 2).
trol in the first and second seasons, but not in the third
season (1998–1999) (Table 2). Total N uptake was signif-
Aboveground Recovery of Mineral
icantly (P 0.05) higher in manure plus N fertilizer
Nitrogen Fertilizer
treatments compared with the control for the three crop-
ping seasons. There was a positive manure N fertilizer
The use efficiency of mineral N fertilizer was only
interaction, which was significant (P 0.001) in the first
determined in the first and second seasons. The use ef-
ficiency averaged 44.7% (25.5–63.8%) for all treatments(1996–1997) and second (1997–1998) cropping seasons,
NYAMANGARA ET AL.: FERTILIZER USE AND N LEACHING IN A TROPICAL SOIL 603
Table 3. Nitrogen fertilizer use efficiency in maize fertilized with
15
N-labeled fertilizer (F) and combinations of cattle manure (M) and
15
N-labeled fertilizer.
Treatments Total N Total N uptake NDFF† NDFF FUE‡
% kgNha
1
%
1996–1997
60 kg N ha
1
0.77 45.4 15.3 33.63 25.5
120 kg N ha
1
0.88 95.2 45.0 47.26 37.5
60 kg N ha
1
F 12.5 Mg ha
1
M 0.70 77.9 24.8 31.82 41.3
120kgNhaF 12.5 Mg ha
1
M 0.69 153.6 69.5 45.25 57.9
60 kg N ha
1
F 37.5 Mg ha
1
M 0.79 90.2 25.3 28.03 42.2
120 kg N ha
1
F 37.5 Mg ha
1
M 1.38 189.1 76.5 40.44 63.8
Significance *** *** *** ** ***
CV, % 6.62 13.9 10.5 14.36 8.6
LSD (P 0.05) 0.06 4.4 4.2 4.93 3.7
1997–1998
60 kg N ha
1
0.53 56.3 11.5 20.35 19.2
120 kg N ha
1
0.92 63.4 23.6 37.24 19.7
60 kg N ha
1
F 12.5 Mg ha
1
M 0.47 105.0 16.7 15.88 27.8
120kgNhaF 12.5 Mg ha
1
M 0.60 133.6 32.2 24.09 26.8
60 kg N ha
1
F 37.5 Mg ha
1
M 0.65 116.0 19.3 16.66 32.2
120 kg N ha
1
F 37.5 Mg ha
1
M 1.00 144.7 41.1 28.40 34.3
Significance ** ** *** *** **
CV, % 13.00 19.8 11.2 8.86 13.3
LSD (P 0.05) 0.15 4.9 5.1 3.83 6.5
** Significant at the 0.01 probability level.
*** Significant at the 0.001 probability level.
† Nitrogen derived from fertilizer.
‡ Fertilizer use efficiency (crop uptake of applied mineral N fertilizer).
in the first season compared with 26.6% (19.2–34.3%) seasons (Fig. 2). Concentrations from lysimeters that
received N fertilizer were higher than the control in thein the second season (Table 3). Fertilizer use efficiency
was calculated as the amount of fertilizer N taken up first (up to mg 22.5 NO
3
–N L
1
) and second seasons
(15.3 mg NO
3
–N L
1
), but during the third season theby aboveground plant parts (NDFF in kg N ha
1
)asa
percentage of total fertilizer N added to soil. For a given concentration was smaller and comparable with the
control lysimeters, that is, 10 mg NO
3
–N L
1
. Kamu-mineral N fertilizer rate, the addition of increasing rates
of manure increased the use efficiency of the mineral kondiwa and Bergstro
¨
m (1994a) also reported lower
N, and this trend was more pronounced in the first
N concentration in leachates from lysimeters receiving
season (Table 3). The overall effects of manure addition
aerobically composted manure (1% N) compared with
on mineral N fertilizer use efficiency are shown in
corresponding lysimeters receiving equal amounts of N
Table 4. The results showed that applying mineral N
as mineral fertilizer, but there are examples showing the
with manure increased the mineral N fertilizer use effi-
opposite situation. For example, in a study performed
ciency by up to 22% in the first year and up to 14% in the
under cold climate conditions, NO
3
–N concentrations
second year compared with when mineral N fertilizer is
in drainage water were larger in poultry manured soils
applied on its own.
than in soils receiving equal amounts of N with mineral
The observed mineral N fertilizer use efficiencies were
fertilizer (Bergstro
¨
m and Kirchmann, 1999). But, it is
within the 25 to 80% range reported elsewhere (Berg-
important to keep in mind that the manures used in that
stro
¨
m, 1987; Kamukondiwa and Bergstro
¨
m, 1994b; Kor-
study and our study were different, which precludes a
enkov et al., 1975; Jokela and Randall, 1997). Kamukon-
direct comparison of the results.
diwa and Bergstro
¨
m (1994b) reported first-season
Manure and N fertilizer treatment combinations re-
average mineral N fertilizer uptake efficiency by maize
sulted in NO
3
–N concentrations in leachate reaching
of 27.3% on similar soils at a nearby site in Zimbabwe,
34.2 mg NO
3
–N L
1
in the first season and 25.2 mg L
1
although the study was conducted during seasons char-
in the second season when the high N fertilizer rate
acterized by long dry spells. Although the
15
N isotope
(120 kg N ha
1
) was used.
technique is known to under- or overestimate mineral
High-intensity rainfall recorded soon after applica-
N fertilizer use efficiency due to the so-called added
tion of the N fertilizer, especially during 1996–1997,
nitrogen interaction (ANI) effect (Jenkinson et al.,
may have leached the soluble N resulting in high NO
3
1985), the error in this study was assumed to be too low
due to the low soil organic matter content of the soil.
Table 4. Overall effects of manure addition on recovery of labeled
fertilizer N in maize fertilized with
15
NH
4
15
NO
3
.
Nitrate Concentration in Leachate
Recovery
Season Control† 12.5 Mg ha
1
37.5 Mg ha
1
LSD (P 0.05)
As expected, NO
3
–N concentrations in leachate were
consistently low (10 mg L
1
) from lysimeters where
%
no N was added (Fig. 2). Concentrations from lysimeters
1996–1997 31.63 47.78 53.73 3.67
1997–1998 19.30 27.45 33.22 4.07
amended with manure were slightly greater (up to 15 mg
† No manure added.
NO
3
–N L
1
) than the control during the three cropping
604 J. ENVIRON. QUAL., VOL. 32, MARCH–APRIL 2003
Fig. 2. Average NO
3
concentrations in leachate collected from replicate lysimeters applied with different amounts of manure and mineral N
fertilizer. Bars represent standard errors.
concentrations in N fertilizer treatments in the first and This indicates that some of the fertilizer N was displaced
by preferential flow induced by an unstable wettingsecond season, although much less than one pore vol-
ume of water had leached through the profile between front (Steenhuis and Parlange, 1991), which was proba-
bly enhanced by the high rainfall intensity.fertilizer application and this breakthrough of water.
NYAMANGARA ET AL.: FERTILIZER USE AND N LEACHING IN A TROPICAL SOIL 605
Table 5. The effect of different manure and N fertilizer rates on
used as the controls. In the first season, 24 to 40% of
NO
3
–N leaching during 1996–1997, 1997–1998, and 1998–1999
the added mineral N was leached, which is socioeco-
cropping seasons.
nomically significant given the poor resource base of
NO
3
–N leaching
smallholder African farmers. In the second and third
N fertilizer application (kg N ha
1
)
seasons, the proportions of fertilizer-derived N leached
were much lower, that is, 3 to 9% and 4 to 11%, respec-
Manure 0 60 120
tively. Overall, the low manure (12.5 Mg ha
1
) plus 60
Mg ha
1
kgNha
1
kg N ha
1
fertilizer treatment was the best treatment in
1996–1997
terms of maintaining dry matter yield and minimizing
0 18.9 41.9 56.3
N leaching losses.
12.5 24.2 48.0 53.6
37.5 27.5 47.5 56.1
It was assumed that the unaccounted for N was re-
LSD (P 0.05) 8.5
tained in the soil since very low gaseous losses (10 kg
1997–1998
Nha
1
) have been reported in manure and unmanured
0 11.8 14.3 15.8
soils locally (Murwira, 1995; Nzuma and Murwira, 2000).
12.5 14.0 16.7 16.9
37.5 16.7 22.1 24.1
LSD (P 0.05) 2.4
CONCLUSIONS
1998–1999
0 12.7 18.9 23.2
Results obtained in this study showed that application
12.5 19.9 22.2 28.2
of mineral N fertilizer to a sandy soil can result in high
37.5 20.0 24.4 32.9
LSD (P 0.05) 5.7
NO
3
leaching losses when all the fertilizer is applied at
planting. By contrast, it was shown that the application
of aerobically composted manure from the smallholder
Nitrate Leaching Losses
farming areas of Zimbabwe to soil does not pose an
Nitrate N leaching losses from lysimeters amended
environmental concern due to NO
3
leaching in the short
with manure and N fertilizer were significantly (P
term, presumably an effect of the high degree of stabili-
0.01) higher than from the control lysimeters during the
zation that occurs during decomposition. Instead, the
three growing seasons (Table 5). During the first season
manure enhanced the use efficiency of mineral N fertil-
(1996–1997), lysimeters with N fertilizer (60 and 120 kg
izer by crops when the two were applied in combination.
Nha
1
) leached significantly (P 0.05) more NO
3
–N
Although the N leaching losses observed in this study
(41.9 and 56.3 kg N ha
1
, respectively) than the manure
may be small in terms of environmental pollution, they
(12.5 and 37.5 Mg ha
1
) treatments (24.2 and 27.5 kg N
are of socioeconomic significance in the smallholder Afri-
ha
1
, respectively). Leaching losses were much lower
can farming systems where N fertilizer is unaffordable to
during the second (11.8–24.1 kg N ha
1
) and third (12.7–
most farmers. The low manure (12.5 Mg ha
1
) plus 60
32.9 kg N ha
1
) seasons, but the N fertilizer and manure
kg N ha
1
fertilizer treatment was the best treatment in
effects were still significant (P 0.01).
terms of maintaining dry matter yield and minimizing
The higher NO
3
–N leaching in the mineral fertilizer
N leaching losses. Further studies are required to deter-
treatments was attributed to the large amounts of readily
mine the effect of manure quality and split application
available N early in the season, whereas most of the
of N fertilizer on plant uptake and leaching losses, and
N derived from manure has to undergo mineralization
also the effect of soil type.
before it becomes available for uptake and leaching. It
is notable that smallholder farmers typically apply one-
ACKNOWLEDGMENTS
third of the mineral N fertilizer at planting and the
This study was conducted within the project “Management
balance at 4 to 6 weeks after planting, and under such
of Soil Organic Matter for Sustainable Agriculture” sponsored
conditions NO
3
leaching may be lower. In this study all
by Swedish Agency for Research and Co-Operation with De-
the mineral N fertilizer was applied at planting.
veloping Countries (SAREC-1995-0743) to which the authors
Although the above N leaching losses in 1997–1998
are grateful. We would also like to thank the Institute of Envi-
and 1998–1999 may be considered low, they are of socio-
ronmental Studies of the University of Zimbabwe for coordi-
nating the project.
economic significance in the smallholder African farm-
ing systems. Under such conditions, maximizing N up-
take (and hence yield) is much more important than
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... We observed reduced leaching of nutrients when the fertilizer was applied to the soil column using foam. This study could pave the road for designing new fertilizer based in foam with a high retention capacity to address the leaching issue in soil especially in coarse-textured areas in the world such as coastal regions which suffer from high leaching rates (Sexton, Moncrief et al. 1996, Nyamangara et al. 2003. Different methods can be followed to apply this new novel method on a large scale. ...
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... The loss of nutrients reduces the maize production system's nutrient use efficiency, resulting in lower grain yields (Tadesse et al., 2013). Since fertilizer is relatively expensive when compared to produce, effective N fertilizer use is important for both agroeconomic and environmental reasons (Nyamangara et al., 2003). Fertilizer should be applied at the prescribed rate for optimum efficiency and productivity. ...
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... A simple t-test also showed that the marginal response to mineral fertiliser nitrogen was significantly lower on fields that used manure (6.4 kg/ha) than on fields without manure (7.5 kg/ha). Nyamangara et al. (2003) showed in Zimbabwe that the ratio of manure and mineral fertiliser N matters as to the dry matter yield and N leaching. Chivenge, Vanlauwe, and Six (2011) did a meta-analysis in SSA and found both positive and negative interactive effects between organic resources and mineral fertiliser depending on soil type, precipitation, amount of organic resources and mineral fertiliser. ...
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While adoption rates for inorganic fertiliser are relatively high in Ethiopia, application rates are generally considered agronomically suboptimal. Using recent data on Ethiopian smallholder maize producers, we showed that maize response to nitrogen, and the profitability of fertiliser use depended on maize agronomy. The agronomic optimum ranged from 0 to 344 kg/ha with a mean value of 209 kg/ha. The actual nitrogen application rates were only about half the agronomic optimum, on average, and were less than the farm-specific economic optimum on 80% of maize fields. The average economic optimum level was 145 kg N/ha, but when we account for risk aversion, the resulting average optimum level is very close to the average observed usage level of 88 kg N/ha. Addressing risk aversion may help to induce greater levels of fertiliser investments at current prices and yield response rates. Our analysis also suggests that key pathways for increasing the economic returns to smallholder fertiliser investments include: complementing nitrogen inputs with phosphorus inputs and improved varieties, using lower levels of nitrogen under intercropping and manure inputs, enabling farmers to delay output sales beyond the immediate post-harvest period, and lowering the costs of accessing input and output markets.
... Agriculture requires NH4 + -N and NO3 --N in large amount to sustain crop growth (Gao et al., 2020). However, NO3 --N is mobile and can be subjected to losses through leaching particularly during rainy period (Nyamangara et al., 2003;Kotlar et al., 2020). Naturally, leguminous plants have the capacity of fixing atmospheric N through symbiotic process, which allow N addition stocks in the soil environment. ...
Thesis
Full-text available
Soil fertility in tropical agroecosystems is often subjected to degradation that leads to nutrient depletion with negative effects on land productivity and food security. This challenge is aggravated by the complexity of socio-economic (market distance, farm typology) and biophysical (agro-ecology, site) conditions causing soil fertility variability. Consequently, blanket fertilizer recommendations cannot be applied in areas of high fertility variability. In this PhD study, methods were harmonized to assess drivers of soil fertility status across regions. Despite being pointed as factors contributing to soil fertility variability, market access, farm typology (resource endowment) and agro-ecology have not been subjected to soil fertility assessment. This PhD study aimed mainly at verifying that these factors have to integrated rather than considered in isolation to enable accurate assessments of soil fertility across spatial scales and socio-economic gradients. It was hypothesized that market distance and farm typology is a determinant of agricultural development in Democratic Republic of Congo (DRC). As market distance is increasing, the soil fertility status of smallholder farming systems decreases despite farmers’ wealth. In a parallel study conducted in Ethiopia, it was complementarily hypothesized that the soil fertility status is also influenced by inter-related effects of agro-ecology and farm typology. As nitrogen (N) is known to be limiting in smallholder farms, conservation and sustainable provision of this nutrient will be essential to achieve niche-based integrated soil fertility management (ISFM) strategies. Therefore, understanding of the ecological processes (proteolysis, nitrification) that control soil N availability through organic residue management in varying soil fertility variability conditions will be essential. Low concentrations of lignin (L) and polyphenols (PP) relative to N have been acknowledged to facilitate decomposition, hence, stimulate the abundance of proteolytic and nitrifying soil microbial communities. Therefore, it was hypothesized that high quality (low (L+PP)/N)) residue applied to high pH soils have a positive relationship between the functional potential of proteolytic enzymatic activities and abundance of nitrifying communities. The survey studies in DRC and Ethiopia were guided by the following objectives; 1) To determine the inter-related influence of market distance and farm typology on soil fertility status of smallholder farming systems of South-Kivu, Eastern DRC. 2) To assess the inter-related effects of agro-ecology and farm typology on soil fertility status across crop-livestock systems in Western and Central Ethiopia. Moreover, to better understand the ecological processes (proteolysis, nitrification) that control N through organic residue management in varying soil fertility variability conditions, an incubation study was performed to meet objective 3) To verify that potential proteolytic enzyme activities modulate archaeal and bacterial nitrifier abundance in soils with differing acidity and organic residue treatment. Results from the soil survey study in DRC revealed a decreasing soil fertility with increasing market distance across all farm typologies. A significant influence of farm typology was found for exchangeable calcium and magnesium, while factor site resulted in a significant difference of plant available phosphorus. Furthermore, factor “site” interacted with market distance for soil organic carbon (SOC) quality indexes. In addition, the interaction of market distance and typology became obvious in the medium wealthy and poor farms. Market distance effects were associated with walking distance, while site effects were attributed to factors such as soil type and climatic conditions. In Ethiopia, inter-related effect of agro-ecology and farm typology was found. Higher total carbon and total nitrogen was found in wealthy farmers’ field compared to poor farmers’ field in the highlands. As an indication of soil quality, lowest SOC stability indexes were revealed in soils of wealthy compared to that from poor farm typology. These differences in soil fertility were attributed to farm management practices among typology classes and agro-ecological zone distinctions. The result from the incubation study revealed a significant relationship of proteolytic enzyme activities with the abundance of ammonia oxidizing bacteria and archaea, even though the extent of this relationship was more dependent on soil pH and incubation time, but not residue quality. This suggests that the effect of soil pH is stronger than that of residue quality on enzyme activity and nitrifiers community, reflecting the importance of soil physico-chemical conditions rather than management practices. The incubation study further showed that nitrifying prokaryotes benefitted from the release of N spurred by proteolysis, and indicated a niche specialization between ammonia oxidizing bacteria and archaea depending on soil acidity and resource availability. Overall, this PhD study showed that market access, typology and agro-ecology were important drivers of soil fertility variability in the study regions of DRC and Ethiopia. However, factor site played a significant role in shaping soil fertility variability, implying that site-specific recommendations could be a way forward for designing soil fertility management in smallholder farmers. It was inferred that prospective niche-based ISFM strategies must consider such contrasting but interrelated factors including, but not limited to agro-ecology, farm typology and market access. This would reduce the effect of soil fertility variability across regions. This PhD study only considered land size (DRC, Ethiopia), livestock and mineral fertilizers (Ethiopia) as key features to define the wealth status of targeted farms; future studies should consider a wider range of socio-economic and biophysical factors including labor availability, off-farm household income and soil management history for more accuracy of soil fertility variability. This will strengthen the accuracy of prospective soil fertility assessments across socio-economic gradients and spatial scales. Finally, it is suggested to extend the results from the incubation study to field conditions considering soils with a broader soil acidity range and organic residues with more distinct biochemical quality. This will verify the given assumptions about the functional relationships between proteolytic and nitrifying soil communities. Overall, the presented PhD study has contributed to ongoing research on best-fit soil fertility recommendations and knowledge gaps about soil ecological functioning, by providing an advanced understanding of driving factors of soil fertility variability and soil microbial functioning in smallholder farms in tropical environments.
... Mitchell et al. (1994) reported that furrow irrigation is a widely used type of irrigation around the world and is considered as a major source of nitrate leaching. Most of the nitrate losses from agricultural soils are undertaken due to leaching (Nyamangara et al., 2003), bypass flow (Sigunga et al., 2008), nitrification (Sigunga et al., 2002b) and ammonia volatilization (Sigunga et al., 2002a). ...
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The development of irrigated agriculture has multi-directional benefits for the economic development of a country. However, it has negative consequences including environmental effects, land degradation, waterlogging, salinization, and social instability when the irrigation water is not properly managed. This research has been conducted at Koga Irrigation Scheme to assess the effect of irrigated agriculture on spatial and temporal fluctuations of the groundwater table and water quality. This study has attempted to highlight the status of spatial and temporal fluctuations of the groundwater table depth at Koga irrigation scheme, Northwest Ethiopia. Purposive representative samples of six shallow wells inside the irrigation scheme and four shallow wells outside the irrigation scheme were selected for evaluation of the impact of irrigation on groundwater table fluctuation and groundwater quality. Arc GIS tool has been applied for interpolation of the spatial variation of the groundwater level. The result of the study clearly showed that irrigation has affected the groundwater level and groundwater quality. For instance, under the irrigated field, a rise in the groundwater table that ranges from 0.77 m to 0.52 m observed compared with non-irrigated field. The groundwater table was found to have high fluctuation in space and time owing to spatial and temporal variation of irrigation amount, soil type, topography, and other factors. The groundwater quality also showed that the concentration of nitrate and sulfate was higher in the irrigated land than non-irrigated land. However, the concentration of the nutrients was below the world health organization drinking water quality parameters. This study indicated the need to pay more attention to the irrigation water management of the scheme to control the groundwater level rise. This study showed that irrigation has effect on groundwater level and there is high spatial and temporal variation of groundwater level in the area. Therefore, continuous follow-ups and assessment of the groundwater table and Physico-chemical properties of the study area is essential for the sustainability of the Koga irrigation scheme and human health of the people who live in the scheme.
... Mitchell et al. (1994) reported that furrow irrigation is a widely used type of irrigation around the world and is considered as a major source of nitrate leaching. Most of the nitrate losses from agricultural soils are undertaken due to leaching (Nyamangara et al., 2003), bypass flow (Sigunga et al., 2008), nitrification (Sigunga et al., 2002b) and ammonia volatilization (Sigunga et al., 2002a). ...
Thesis
The development of irrigated agriculture has multi-directional benefits for the economic development of a country. However, it has negative consequences including environmental effects, land degradation, waterlogging, salinization, and social instability when the irrigation water is not properly managed. This research has been conducted at Koga Irrigation Scheme to assess the effect of irrigated agriculture on spatial and temporal fluctuations of the groundwater table and water quality. This study has attempted to highlight the status of spatial and temporal fluctuations of the groundwater table depth at Koga irrigation scheme, Northwest Ethiopia. Purposive representative samples of six shallow wells inside the irrigation scheme and four shallow wells outside the irrigation scheme were selected for evaluation of the impact of irrigation on groundwater table fluctuation and groundwater quality. Arc GIS tool has been applied for interpolation of the spatial variation of the groundwater level. The result of the study clearly showed that irrigation has affected the groundwater level and groundwater quality. For instance, under the irrigated field, a rise in the groundwater table that ranges from 0.77 m to 0.52 m observed compared with non-irrigated field. The groundwater table was found to have high fluctuation in space and time owing to spatial and temporal variation of irrigation amount, soil type, topography, and other factors. The groundwater quality also showed that the concentration of nitrate and sulfate was higher in the irrigated land than non-irrigated land. However, the concentration of the nutrients was below the world health organization drinking water quality parameters. This study indicated the need to pay more attention to the irrigation water management of the scheme to control the groundwater level rise. This study showed that irrigation has effect on groundwater level and there is high spatial and temporal variation of groundwater level in the area. Therefore, continuous follow-ups and assessment of the groundwater table and Physico-chemical properties of the study area is essential for the sustainability of the Koga irrigation scheme and human health of the people who live in the scheme.
... Mitchell et al. (1994) reported that furrow irrigation is a widely used type of irrigation around the world and is considered as a major source of nitrate leaching. Most of the nitrate losses from agricultural soils are undertaken due to leaching (Nyamangara et al., 2003), bypass flow (Sigunga et al., 2008), nitrification (Sigunga et al., 2002b) and ammonia volatilization (Sigunga et al., 2002a). ...
Thesis
The development of irrigated agriculture has multi-directional benefits for the economic development of a country. However, it has negative consequences including environmental effects, land degradation, waterlogging, salinization, and social instability when the irrigation water is not properly managed. This research has been conducted at Koga Irrigation Scheme to assess the effect of irrigated agriculture on spatial and temporal fluctuations of the groundwater table and water quality. This study has attempted to highlight the status of spatial and temporal fluctuations of the groundwater table depth at Koga irrigation scheme, Northwest Ethiopia. Purposive representative samples of six shallow wells inside the irrigation scheme and four shallow wells outside the irrigation scheme were selected for evaluation of the impact of irrigation on groundwater table fluctuation and groundwater quality. Arc GIS tool has been applied for interpolation of the spatial variation of the groundwater level. The result of the study clearly showed that irrigation has affected the groundwater level and groundwater quality. For instance, under the irrigated field, a rise in the groundwater table that ranges from 0.77 m to 0.52 m observed compared with non-irrigated field. The groundwater table was found to have high fluctuation in space and time owing to spatial and temporal variation of irrigation amount, soil type, topography, and other factors. The groundwater quality also showed that the concentration of nitrate and sulfate was higher in the irrigated land than non-irrigated land. However, the concentration of the nutrients was below the world health organization drinking water quality parameters. This study indicated the need to pay more attention to the irrigation water management of the scheme to control the groundwater level rise. This study showed that irrigation has effect on groundwater level and there is high spatial and temporal variation of groundwater level in the area. Therefore, continuous follow-ups and assessment of the groundwater table and Physico-chemical properties of the study area is essential for the sustainability of the Koga irrigation scheme and human health of the people who live in the scheme.
... Mitchell et al. (1994) reported that furrow irrigation is a widely used type of irrigation around the world and is considered as a major source of nitrate leaching. Most of the nitrate losses from agricultural soils are undertaken due to leaching (Nyamangara et al., 2003), bypass flow (Sigunga et al., 2008), nitrification (Sigunga et al., 2002b) and ammonia volatilization (Sigunga et al., 2002a). ...
Thesis
The development of irrigated agriculture has multi-directional benefits for the economic development of a country. However, it has negative consequences including environmental effects, land degradation, waterlogging, salinization, and social instability when the irrigation water is not properly managed. This research has been conducted at Koga Irrigation Scheme to assess the effect of irrigated agriculture on spatial and temporal fluctuations of the groundwater table and water quality. This study has attempted to highlight the status of spatial and temporal fluctuations of the groundwater table depth at Koga irrigation scheme, Northwest Ethiopia. Purposive representative samples of six shallow wells inside the irrigation scheme and four shallow wells outside the irrigation scheme were selected for evaluation of the impact of irrigation on groundwater table fluctuation and groundwater quality. Arc GIS tool has been applied for interpolation of the spatial variation of the groundwater level. The result of the study clearly showed that irrigation has affected the groundwater level and groundwater quality. For instance, under the irrigated field, a rise in the groundwater table that ranges from 0.77 m to 0.52 m observed compared with non-irrigated field. The groundwater table was found to have high fluctuation in space and time owing to spatial and temporal variation of irrigation amount, soil type, topography, and other factors. The groundwater quality also showed that the concentration of nitrate and sulfate was higher in the irrigated land than non-irrigated land. However, the concentration of the nutrients was below the world health organization drinking water quality parameters. This study indicated the need to pay more attention to the irrigation water management of the scheme to control the groundwater level rise. This study showed that irrigation has effect on groundwater level and there is high spatial and temporal variation of groundwater level in the area. Therefore, continuous follow-ups and assessment of the groundwater table and Physico-chemical properties of the study area is essential for the sustainability of the Koga irrigation scheme and human health of the people who live in the scheme. Keywords: Groundwater Level; Groundwater Quality; Koga; Nutrient Concentration
... An increase of 20 and 34% was observed in the years 2015 and 2016. Laird et al. (2001) and Nyamangara et al. (2003) have also reported improvements of agricultural soils when they are amended with compost and other organic materials. The amendments improved the physical, chemical, and biological properties and water saving capacity of the soil, which enhances the long-term sustainability of agriculture. ...
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Sandy soils are considered marginal, owing to their low soil fertility, due to their low soil organic carbon and clay contents. The marginality is particularly pronounced when sandy soils exist in hot and arid environments, such as in the UAE and other GCC countries. Three field trials were undertaken in three agricultural seasons, i.e., 2014, 2015, and 2016, on sandy soils, employing various combinations of organic and inorganic soil amendments. The procedures used for the recycling green and date palm residues to compost and biochar, as well as their beneficial uses, are presented and discussed. The addition of organic amendments increased plant growth, height, fresh biomass, and grain yield in quinoa, cowpea, and lablab-bean. The combined use of compost and biofertilizer has a significant impact when compared to biofertilizer application alone. The use of Sharjah-compost can be a viable option and environment friendly method to improve soil health. The use of organic amendments significantly affected organic carbon build up and increased plant growth parameters, which indicate its positive impact on sandy soils.
... helps to restore soil structural stability, reduce soil bulk density (Tejada and Gonzalez, 2007), increase soil aggregate stability and organic C content (Annabi et al., 2011), increase productivity (Ryals and Silver, 2013) and stimulate microbial activity (Bastida et al., 2008). Therefore, inappropriate application poses the risk of increased soil CO 2 and N 2 O emissions (Jones et al., 2005) and nitrate (NO 3 − ) leaching (Nyamangara et al., 2003). Another management option to reduce fertilizer application and to potentially improve the soil GHG balance is planting leguminous species. ...
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Studies of soil greenhouse gas (GHG) fluxes (CO2, CH4 and N2O) from tropical soils are still scarce and the effects of urban green space management on soil GHG fluxes are poorly addressed. In order to establish reliable global GHG budgets, field measurements of soil GHG fluxes from different land uses and management practices in tropical regions are urgently needed. In this study, soil fluxes of CO2, CH4 and N2O were measured over a period of one year, from a forest and an urban parkland in Singapore. At the parkland site, two additional management practices were investigated, namely compost application to urban lawn and the replacement of lawn by legumes. The average CO2 efflux from the forest soil was 0.17 ± 0.01 g C m⁻² h⁻¹ and was 30% lower than that of the parkland soil. The forest soil was a CH4 sink (−36.03 ± 8.80 μg C m⁻² h⁻¹), while the parkland soil was a source of CH4 (43.79 ± 9.66 μg C m⁻² h⁻¹). Both soils were net emitters of N2O, with the forest soil releasing four times more N2O (23.23 ± 5.10 μg N m⁻² h⁻¹) than the parkland soil (6.47 ± 2.52 μg N m⁻² h⁻¹). During the entire observation period, compost application increased CO2eq by 30% compared with the untreated parkland soil. Shortly after compost addition, CO2 fluxes significantly increased and remained elevated until the end of the experiment. Soil CH4 emissions also increased, but the effect was small compared to CO2 (<1% CO2eq). Compost amendment caused an immediate short-term peak of N2O emissions. However, after the first day, which was characterized by a heavy rain event, the compost effect on N2O production was negligible. Compared to grass cultivation, legume planting resulted in a 20% reduction of CO2eq. This study shows that conserving mature secondary forests and the cultivation of herbaceous legumes on tropical urban soils, where open lawn spaces are not required, can reduce soil GHG emissions.
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Inorganic N fertiliser may be applied to soil in addition to cattle manure by smallholder farmers in developing countries: (a) to complement fertilization; (b) to control a possible immobilisation of N by the manure; and (c) to eliminate the risk of yield depression due to lack of plant available N. The aim of this study was to find out if and how much N was immobilised by cattle manure, if and when remineralisation of N will take place and, if added N has an effect on decomposition of cattle manure in soil. A laboratory study was conducted applying inorganic N fertiliser to soil (NH4NO3 equivalent to 30, 60 and 120 kg N ha-1) together with four cattle manures with different C/N ratios (9–18). CO2–C mineralisation and changes of inorganic N in soil were determined over 60 d. Immobilisation of fertiliser N occurred with manure having the lowest C/N ratio but not with the manures having a higher C/N ratios. Maximum immobilization of fertiliser N (23–36%) occurred within 21 d and thereafter N was mineralised. Carbon dioxide evolution decreased in cattle manure-amended soil at increasing rates of N fertiliser, but decomposition was still higher than from the unamended control. None of the manure treated soils had significantly different contents of inorganic N after 2 months of incubation. It was not possible to use the C/N ratio of aerobically decomposed cattle manure as a tool to predict mineralization or immobilization of N. It was concluded that aerobically decomposed solid cattle manures do not contribute to the N supply of crops in the short term but can immobilize fertiliser N applied at the same time.
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A field study was conducted on an Enosburg fine sandy loam (Mollic Haplaquent) in northwestern Vermont to evaluate the effect of dairy-manure and N-fertilizer application on corn yields and soil profile NO3 in a silage production system. Yields and N uptake were increased by N fertilizer and by manure. Plant uptake of N followed a similar pattern but with somehwat more pronounced effects. Sampling of the 1.5-m soil profile before planting and after harvest showed increases in soil NO3 that were related to the amounts of manure and fertilizer N applied. Some decreases in NO3 were measured from fall to spring sampling times. Application of manure resulted in similar or slightly lower soil profile NO3 than agronomically equivalent rates of fertilizer N. -from Author
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A lysimeter experiment was conducted to determine the magnitude of fertilizer-N leaching over a three-year period. Three types of lysimeters and two treatments were included, i.e., barley and a grass ley fertilized with calcium nitrate at rates of 120 and 120+80 kg N ha yr, respectively. The N-fertilizer applied during the first year had 15-N enrichments ranging from ca. 1 to 99% atom excess (a.e.). 15-N-labeled fertilizer (ca. 99% 15-N a.e.) was also applied to three grass ley lysimeters (not fertilized with 15-N earlier) during the third year. Approximately 10% of the nitrate leached from lysimeters with barley during the first year originated from fertilizer. Dry weather during the first two years reduced N-leaching substantially. Leaching of 15-N-labeled fertilizer never exceeded 1 kg N ha yr from either the barley or the grass ley lysimeters. A maximum of 1.2% of the 15-N-labeled fertilizer applied to the barley was recovered in drainage water during the three years of the study. The grass ley generally had lower proportions of nitrate-N derived from fertilizer in drainage water compared with barley. The amounts of fertilizer-N appearing in drainage water were similar for each type of lysimeter and each level of 15-N enrichment.
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Fertilizer use in the semi-arid tropics is considered risky because of the unreliable rainfall pattern. A flexible system of fertilization was devised which allowed for high yields in wet years, and reduced financial losses in dry years. Relatively immobile nutrients, such as phosphorus, potassium and sulphur, were applied at rates determined from generalized soil properties and the total nutrient uptake required for a crop to achieve its maximum yield potential in a season with average rainfall. Nitrogen was applied as a series of split applications, which were adjusted during the season according to the degree of water stress observed. This approach was tested in on-farm trials for maize production on nutrient-poor sandy soils in three regions of Zimbabwe, and resulted in larger yields and profits than current recommendations, providing an accept able level of financial return. Small further yield increases were possible, at acceptable returns, when these fertilizer practices were combined with the establishment of tied-ridges by ox-drawn implements, 30 days after planting. By careful estimation of yield potential, and appropriate adjustments to soil fertility, this system of soil management could be applied to other cropping situations and other areas with variable rainfall. Uso de fertilizantes para condiciones de precitación variable
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Leaching of nitrate from a sandy loam cropped with spring barley, winter wheat and grass was compared in a 4-year lysimeter study. Crops were grown continuously or in a sequence including sugarbeet. Lysimeters were unfertilized or supplied with equivalent amounts of inorganic nitrogen in calcium ammonium nitrate (CAN) or animal slurry according to recommended rates (1N) or 50% above recommended rates (1.5N). Compared with unfertilized crops, leaching of nitrate increased only slightly when 1N (CAN) was added. Successive annual additions of 1.5N (CAN) or 1N and 1.5N (animal slurry) caused the cumulative loss of nitrate to increase significantly. More nitrate was leached after application of slurry because organic nitrogen in the slurry-was mineralized. With 1N (CAN) the leaching losses of nitrate were in the following order: continuous spring barley undersown with Italian ryegrass < continuous ley of perennial ryegrass < spring barley in rotation and undersown with grass < perennial ryegrass grown in rotation = winter wheat grown in rotation < sugarbeet in rotation < continuous winter wheat < continuous barley < bare fallow. At recommended levels of CAN (1N), cumulative nitrate losses over the four years were similar for the crops when grown in rotation or continuously. When crops received 1.5N (CAN) or animal slurry, nitrate losses from the crops grown continuously exceeded those from crops in rotation. Including a catch crop in the continuous cropping system eliminated the differences in nitrate leaching between the two cropping systems.