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Legume Decomposition and Nitrogen Release When Applied as Green Manures to Tropical Vegetable Production Systems

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For legume green manures (GM) to be effective, environmentally sound N sources for horticultural crops in the tropics, their N release must be in synchrony with crop N demand. Decomposition and N release of surface applied (mulch) or incorporated soybean [Glycine max (L.) Merr.] and indigofera (Indigofera tinctoria L.) GM were studied in six field studies conducted at three locations in Taiwan and the Philippines between 1993 and 1995. Litter bags and inorganic N soil samplings were used in order to understand tomato (Lycopersicon esculentum Mill.) crop responses to GM N. Resulting soil N contents were compared with a control (no GM, no fertilizer). The N content of 60 to 74 d soybean GM varied between 110 and 140 kg N ha-L and that of indigofera between 5 and 40 kg N ha(-1). Nitrogen-15-labeled soybean GM was traced in the soil and in organic matter fractions (humic acids, calcium humates, humins) in one of the field studies. Soybean and indigofera decomposed rapidly, losing 30 to 70% of their biomass within 5 wk after application, depending on GM placement, season (wet vs. dry), and location. Soil nitrate contents increased corresponding to GM N release at all locations and seasons, with a maximum increase of 80 to 100 kg NO3-N ha(-1) with incorporated soybean. The peak N release occurred 2 to 6 wk after GM application in two of the three locations, and 5 to 8 wk in the third location. The apparent decline of GM N release at all locations and seasons 8 wk after application was only partly caused by tomato N uptake. At tomato harvest, 30 to 60% of the GM N-15 was found in the soil, and was found mostly in humins. Comparable N release dynamics across seasons and locations suggest a possible N fertilizer substitution by incorporated soybean GM for basal N application and first side dressing to tomato. With respect to season and location, GM N should be supplemented with N fertilizer starting after 8 wk to ensure optimal tomato yields.
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THO
¨NNISSEN ET AL.: LEGUME GREEN MANURES IN TROPICAL VEGETABLE PRODUCTION
253
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Wien, H.C., and P.L. Minotti. 1987. Growth, yield and nutrient uptake
Legume Decomposition and Nitrogen Release When Applied as Green Manures
to Tropical Vegetable Production Systems
Carmen Tho
¨nnissen, David J. Midmore, Jagdish K. Ladha, Daniel C. Olk, and Urs Schmidhalter*
ABSTRACT alogy and acidity, biological activity, and the presence
of other nutrients (Myers et al., 1994). In a previous
For legume green manures (GM) to be effective, environmentally
study, 60-d-old soybean [Glycine max (L.) Merr.] and
sound N sources for horticultural crops in the tropics, their N release
indigofera (Indigofera tinctoria L.) plants conformed to
must be in synchrony with crop N demand. Decomposition and N
high-quality litter characteristics (Swift, 1987), releasing
release of surface applied (mulch) or incorporated soybean [Glycine
max (L.) Merr.] and indigofera (Indigofera tinctoria L.) GM were
N quickly to two of the three soils tested (Tho
¨nnissen
studied in six field studies conducted at three locations in Taiwan and
Michel, 1996). Legume biomass accumulation and
the Philippines between 1993 and 1995. Litter bags and inorganic N
chemical composition (e.g., C/N, N, lignin, polyphenol,
soil samplings were used in order to understand tomato (Lycopersicon
and tannin) of plants of the same age varied between
esculentum Mill.) crop responses to GM N. Resulting soil N contents
location and growing season (Tho
¨nnissen Michel, 1996),
were compared with a control (no GM, no fertilizer). The N content
making it difficult to predict their decomposition when
of 60 to 74 d soybean GM varied between 110 and 140 kg N ha
1
grown under different conditions. Residue decomposi-
and that of indigofera between 5 and 40 kg N ha
1
. Nitrogen-15-
tion can be governed to some extent by GM placement
labeled soybean GM was traced in the soil and in organic matter
on the soil surface (mulch) or incorporation into the
fractions (humic acids, calcium humates, humins) in one of the field
soil (Wilson and Hargrove, 1986). In the southeast of the
studies. Soybean and indigofera decomposed rapidly, losing 30 to 70%
of their biomass within 5 wk after application, depending on GM
USA, the greatest N release from decomposing legumes
placement, season (wet vs. dry), and location. Soil nitrate contents
occurred 2 to 5 wk after cover crop killing in spring
increased corresponding to GM N release at all locations and seasons,
(Sarrantonio and Scott, 1988). Too rapid GM N release
with a maximum increase of 80 to 100 kg NO
3
–N ha
1
with incorpo-
(e.g., within 15 d after incorporation of vetch; Varco et
rated soybean. The peak N release occurred 2 to 6 wk after GM
al., 1989), strong N immobilization after GM addition
application in two of the three locations, and 5 to 8 wk in the third
(Mary and Recous, 1994), or early decline of mineral
location. The apparent decline of GM N release at all locations and
N level over the growing season (Ebelhar et al., 1984)
seasons 8 wk after application was only partly caused by tomato N
lead to poor synchronization between N release and
uptake. At tomato harvest, 30 to 60% of the GM
15
N was found in
crop N demand. Studies evaluating the fate of
15
N from
the soil, and was found mostly in humins. Comparable N release
legume residues decomposing under field conditions led
dynamics across seasons and locations suggest a possible N fertilizer
substitution by incorporated soybean GM for basal N application and
to the conclusions that 30% of legume N was recov-
first side dressing to tomato. With respect to season and location,
ered by a subsequent nonlegume crop and large
GM N should be supplemented with N fertilizer starting after 8 wk
amounts of legume N were retained in soil, mostly in
to ensure optimal tomato yields.
organic forms (Harris et al., 1994; Ladd et al., 1983;
Mueller and Sundman, 1988). If, however, lower miner-
alization rates of mulched GM (nontillage) are responsi-
F
or legume green manures (GM) to be considered ble for reduced inorganic N accumulation, then such a
as effective N sources for horticultural crops, they system could better conserve organic N in the long term
must supply sufficient N and their N release must be in (Sarrantonio and Scott, 1988).
synchrony with vegetable N demand. Green manure The objective of this study was to monitor legume GM
decomposition and subsequent N release depend largely decomposition and determine the timing and quantity of
on residue quality and quantity, soil moisture and tem- GM N release in fields grown to tomato crops (Tho
¨nnis-
perature, and specific soil factors such as texture, miner- sen Michel, 1996) at three locations and two seasons
(wet season, WS; dry season, DS) in Taiwan and the
Philippines. In the tropical WS in Taiwan, nitrate leach-
C. Tho
¨nnissen and D.J. Midmore, The Asian Vegetable Res. & Dev.
Ctr., P.O. Box 42, Shanhua Tainan, Taiwan ROC; J.K. Ladha and
D.C. Olk, IRRI, P.O. Box 933, Manila 1099, Philippines; U. Schmid-
Abbreviations: AVRDC, Asian Vegetable Research and Develop-
halter, Dep. of Plant Nutrition, Technische Universita
¨tMu
¨nchen,
ment Center; BRCI, Bukidnon Resources Corporation, Inc.; DS, dry
Freising-Weihenstephan, D-85350 Germany. Received 12 Aug. 1998.
season; IRRI, International Rice Research Institute; GM, [legume]
*Corresponding author (schmidhalter@weihenstephan.de).
green manure; MMSU, Mariano Marcos State University; SOM, soil
organic matter; WS, wet season.Published in Agron. J. 92:253–260 (2000).
254
AGRONOMY JOURNAL, VOL. 92, MARCH–APRIL 2000
42, 62 and 75 d after GM application, at AVRDC DS 0, 7,
ing losses were estimated in tomato plots amended with
21, 35, 56, 98 d after GM application, and at MMSU 0, 5, 21,
GM and N fertilizer. To trace the fate of GM N at one
36, 58, 77, 113 d after GM application. On each date two
of the three locations,
15
N-labeled GM was traced in soil
randomly chosen bags per treatment were retrieved, oven-
and labile fractions of soil organic matter.
dried at 60C for 48 h, and weighed. Samples were ashed by dry
combustion in a muffle furnace (500C) for 8 h to determine
original ash-free dry weight remaining (Aber et al., 1990).
MATERIALS AND METHODS
Biomass loss data for soybean and indigofera were fitted into
Field Trials
the first-order single exponential model M
t
M
0
e
kt
described
for litter decomposition by Wieder and Lang (1982). The
Legume GM decomposition and subsequent N release to higher the k-value (decomposition rate), the faster the decom-
soil grown to tomato (Lycopersicon esculentum Mill.) crops position of the organic matter. Decomposition rates were cal-
was monitored in six field experiments during 1993 to 1995 culated for a period of 77 d in the WS and 94 d in the DS at
conducted at the Asian Vegetable Research and Development AVRDC and 113 d at MMSU.
Center (AVRDC) in central Taiwan, the Mariano Marcos
State University (MMSU) in northern Luzon in the Philip-
Inorganic Nitrogen
pines, and the Bukidnon Resources Co., Inc. (BRCI), in north-
ern Mindanao in the Philippines. Experiments were run simul- The effects of legume species and GM placement treatments
taneously on two fields, each with different bed systems: raised on the quantity and the timing of N release to soil were evalu-
or low beds. The raised beds were 45 cm high and 2 m wide, ated in all six field experiments. Inorganic N in the soil was
with 2-m furrows between the beds. The furrows were sown monitored in plots planted to tomato in five treatments; con-
with rice (Oryza sativa L.) and were permanently flooded. trol (Ck0), soybean incorporation (Si), soybean mulch (Sm),
The low beds were 20 cm high and 2 m wide, with 50-cm-wide and either indigofera incorporation (Ii) and indigofera mulch
irrigation furrows between beds. Both experiments (raised (Im) (at AVRDC and MMSU) or mungbean incorporation
and low beds) were adjacent, such that the soil type, the (Mi) and mungbean mulch (Mm) (at BRCI). These plots were
cropping history, and meteorological conditions were the sampled on the dates listed above for litterbag sampling and
same. Soil types were a silt-loamy, mixed, hyperthermic Fluva- also at 0, 14, 28, 42, 56, 70, 84, 96, 110 d after GM application
quentic Entochrept (AVRDC); a clayey, kaolinitic, isohyper- at BRCI. Soil samples were collected with a 5-cm-diameter
thermic Ultisol (BRCI); and a clayey, mixed, isohyperthermic auger at the 0- to 30-cm depth from the five treatments in all
Fluvaquentic Ustropept (MMSU). A randomized complete four blocks. Each sample was a mixed composite collected
block design with four replicates was used at all three locations. from four locations in each plot. Soil samples were passed
Treatments at each location were two legume species, two through a 10-mm sieve and extracted with 1 MKCl (1:1.5 soil/
methods of GM application to the soil, and four N treatments water); inorganic N (NH
4
–N and NO
3
–N) was determined with
(0, 30, 60, and 120 kg N ha
1
) applied to tomato. Legumes an ammonia gas sensing electrode (Siegel, 1980). At MMSU,
were grown for 2 mo, cut at the root level, chopped, and additional soil samples from the 30- to 60-cm soil depth were
applied to the soil. The legumes were soybean and indigofera taken at 74 (legume seeding), 1, and 113 d after GM appli-
at AVRDC and MMSU, and soybean and mungbean [Vigna cation.
radiata (L.) Wilcz.] at BRCI. Once GM was applied to the To study the effect of living plants on N mineralization, the
soil, tomato crops were transplanted on the same location and five treatment plots in Blocks I, II, and III were split into
grown up to harvest (2–3 mo) (Tho
¨nnissen Michel, 1996). three subplot treatments after GM application: (i) unplanted,
Leguminous green manures (60 d old at AVRDC; 70 d old (ii) planted with tomato, and (iii) planted with cabbage (Bras-
at MMSU) were incorporated by soil tillage down to the 10- sica oleracea var. capitata L.) in the DS at AVRDC; and (i)
to 15-cm soil depth or left as mulch on the soil surface (no unplanted, (ii) planted with tomato 1 d after GM application,
soil tillage). The amounts of legume biomass and N present as and (iii) planted with tomato 2 wk after GM application at
GM varied across locations and seasons. For example, soybean MMSU. Nitrogen mineralization was monitored in all three
GM contained between 110 and 140 kg N ha
1
, indigofera subplot treatments.
between 5 and 40 kg N ha
1
, and mungbean 26 kg N ha
1
(Tho
¨nnissen Michel, 1996). Tomato seedlings were trans-
Estimation of Potential Nitrate Leaching
planted immediately after GM application and remained in
the field until fruit harvest. Nitrate leaching in the WS at AVRDC was estimated by
the NaCl method (Cameron and Wild, 1982). Fifty grams of
NaCl was broadcast on 1 m
2
in the tomato plots in the treat-
Environmental Monitoring
ments Si, Sm, Ck0, and 120 kg N ha
1
(Ck120) in four replica-
Soil moisture was monitored with tensiometers placed in tions in two bed systems, low or raised beds (Tho
¨nnissen
GM and control treatments, at the 15-, 30- and 45-cm depths Michel, 1996). Sodium chloride was applied on the respective
following tomato transplanting at AVRDC and MMSU. plots after soybean incorporation and mulch on 23 June 1993.
Soil samples were taken on 21 June, 23 July, and 30 August
from the 0- to 50-cm layer in the raised beds and from the 0-
Decomposition Study
to 30-cm layer in the low beds. In each, the soil core was
Nylon bags (mesh size 1 mm) containing 15 g fresh plant separated into 10-cm sublayers. Soil samples were air-dried
material (4.7–5.5 g dry wt.) were used to determine biomass and extracted (1:2 soil/water). Chloride in the water extracts
breakdown of incorporated or mulched soybean and in- was determined with a chloride analyzer (Chloride Analyzer
digofera GM at AVRDC in both the WS and the DS and at 926, Coramed AG, Dietlikon, Switzerland).
MMSU in the DS only. Bags were filled with root and shoot
material on the same day as GM application. Mulch treat-
Nitrogen-15 Experiment
ments contained shoot material only. At the time of GM
application, all bags were either buried 10 cm deep for incorpo- Tomato N response to GM was low in the DS at AVRDC
(Tho
¨nnissen Michel, 1996). To understand the fate of GM N,ration treatments or left on the surface for the mulch treat-
ments. Litter bags were sampled at the same dates as soil soybean GM was labeled with
15
N (Tho
¨nnissen Michel, 1996)
for a
15
N microplot experiment at MMSU. Microplots (metalsampling for inorganic N: at AVRDC WS 0, 2, 5, 8, 14, 29,
THO
¨NNISSEN ET AL.: LEGUME GREEN MANURES IN TROPICAL VEGETABLE PRODUCTION
255
Fig. 1. Decomposition of soybean and indigofera residues when used as mulch or incorporated into the soil in the low and raised bed systems
and in the wet and dry seasons at AVRDC, Taiwan, and in the dry season at MMSU, Philippines (1993–1995). Error bars indicate LSD (0.05).
frames 0.8 by 0.8 by 0.3 m, length by width by height, pushed
species at AVRDC, while soybean and indigofera de-
into the soil to a depth of 25 cm) were amended with
15
N-
composed differently at MMSU. Great differences in
labeled soybean GM. The GM was incorporated manually
decomposition between incorporated and mulched indi-
down to the 10- to 15-cm soil depth. Two tomato seedlings
gofera occurred during the early decomposition stages
were transplanted into each microplot. Green manure
15
N
(up to 6 wk) at MMSU (Fig. 1). With the exception of
recovery in tomato was determined (Tho
¨nnissen Michel,
incorporated indigofera, GM at MMSU decomposed at
1996). Soil was sampled for organic matter extraction and
reduced rates compared with those at AVRDC.
soil
15
N determination in control and soybean incorporation
treatment plots at 1 and 113 d after GM application. Nitrogen-
15 determination was conducted on mobile humic acids
Soil Moisture and Nitrogen Release
(MHA) and calcium humates (CaHA), which were considered
Frequent irrigation precluded significant changes in
as C pools representing early and later stages of the humifica-
soil moisture due to GM placement during the tomato
tion process (Olk et al., 1995).
growing season in the DS at AVRDC and at MMSU.
An optimal water supply for tomato plants was ensured
Statistical Analysis
by maintaining soil matric potentials between 0.02 and
Data were analyzed by ANOVA procedure using JMP Ver-
0.06 MPa. With the exception of typhoons that hit
sion 2 (SAS Inst., 1989) and SAS version 6.03 (SAS Inst., 1991).
southern Taiwan irregularly and subsequently flooded
the low beds, soil matric potentials ranged between
RESULTS
0.01 and 0.08 MPa in the WS. Daily rainfall led to
soil moisture contents near field capacity during the
At all locations and seasons, incorporated GM de-
tomato growing season at the BRCI location.
composed significantly faster than mulched GM (Fig.
Nitrate was the dominant form of inorganic N in the
1). Biomass loss patterns and decomposition rates of
soil soon after legume application at all three locations.
both legume species and GM management practices
Soil NH
4
–N contents remained low (5kgNH
4
–N ha
1
were comparable across bed systems at AVRDC (Table
at AVRDC and MMSU; 20 kg NH
4
–N ha
1
at BRCI)
1). Soybean decomposed slightly faster than indigofera
and were comparable to those of the control (data not
in the WS, but slower than indigofera in the DS at
shown). Green manure application increased soil
AVRDC. Differences in biomass breakdown between
NH
4
–N contents significantly by 10 to 15 kg NH
4
–N ha
1
GM placement (mulch vs. incorporation) at AVRDC
at AVRDC, 5 kg NH
4
–N ha
1
at MMSU, and 30 kg
were larger in the DS than in the WS. While decomposi-
NH
4
–N ha
1
at BRCI in the first week after GM applica-
tion rates of incorporated GM were similar across sea-
tion, but NH
4
–N declined rapidly within 3 wk. With the
sons at AVRDC, those of mulched soybean GM in the
exception of an increase in soil NH
4
–N by 1 to 8 kg
DS were only half those of the WS, and slightly greater
NH
4
–N ha
1
in the low beds in the DS at AVRDC,
than those of the WS for indigofera. The effect of GM
placement on biomass loss was similar across legume NH
4
–N contents did not differ between planted and
256
AGRONOMY JOURNAL, VOL. 92, MARCH–APRIL 2000
Table 1. Decomposition rate, k, of legume green manures (soybean, indigofera) incorporated into the soil or left as mulch on the soil
surface in field experiments at AVRDC, Taiwan (1993–1994) and at MMSU, Philippines (1994–1995). Decomposition rates were
calculated using the single exponential model for decomposition (Wieder and Lang, 1982), for a period of 77 d in the wet season
(WS) and 94 d in the dry season (DS) at AVRDC and 113 d at MMSU.
Species Plant age d† Application Location Season Bed system k‡d
ms1
r
2
§
Soybean 68 incorporation AVRDC WS raised 0.0272a 0.89***
low 0.0361a 0.88***
60 DS raised 0.0236c 0.95***
low 0.0251c 0.80*
74 MMSU DS low 0.0099e 0.96***
68 mulch AVRDC WS raised 0.0175b 0.91***
low 0.0144b 0.90***
60 DS raised 0.0094d 0.89**
low 0.0071d 0.95***
74 MMSU DS low 0.0065f 0.64*
Indigofera 68 incorporation AVRDC WS raised 0.0266g 0.88***
low 0.0262g 0.93***
60 DS raised 0.0313i 0.94**
low 0.0350i 0.97***
74 MMSU DS low 0.0259k 0.67*
68 mulch AVRDC WS raised 0.0098h 0.75**
low 0.0111h 0.91***
60 DS raised 0.0162j 0.98***
low 0.0147j 0.95**
74 MMSU DS low 0.0059l 0.52NS
† d, days after sowing.
k-values within the same season, location, and bed system were compared using a pairwise t-test for slopes. K-values with different letters are significantly
different at P0.05.
§ *,**,***, NS, Regressions are significant at P0.05, 0.01, 0.001, or nonsignificant, respectively.
unplanted plots in the raised beds at AVRDC and at the end of the experiment. At tomato harvest, less soil
NO
3
was found in planted than in unplanted plots, butMMSU.
At all three locations, N release in soil peaked at 80 differences were not significant. Green manure applica-
tion did not affect NH
4
contents at the 30- to 60-cmto 120 kg NO
3
–N ha
1
with soybean GM (Fig. 2). This
peak N release occurred 2 to 6 wk after GM application soil depth.
in both seasons at AVRDC and at BRCI. At MMSU,
Nitrate Leaching
GM N release peaks were delayed relative to the two
other locations, occurring after 5 to 8 wk. Nitrate con- The potential for nitrate leaching estimated from the
tents declined after 5 to 8 wk at all locations. More movement of chloride followed similar patterns in con-
NO
3
–N was released with incorporated GM than trol, 120 kg N ha
1
, soybean mulch and incorporation
mulched GM at AVRDC and MMSU. Far more N was treatments. Therefore, chloride loss (%) data of these
released with soybean than indigofera in the WS at four treatments were averaged for each sampling date
AVRDC; in the DS, however, differences in N release and bed system (Table 2). The background Cl-concen-
between legume species were small. Nitrate released tration (21 June) in the 10- to 50-cm soil depth was
with soybean GM was comparable to that released with rather low. Of the applied chloride, 42 and 50%, had
been lost by 23 July 1993 from a soil depth of 30 and
mungbean GM at BRCI. Basal N mineralization
50 cm, respectively, in the raised bed only 1 mo after
(NO
3
–N) in control treatment plots was low in the WS application. The greatest net loss occurred at the 0- to
at AVRDC and at MMSU, but high in the DS at 10-cm soil depth, whereas chloride accumulation oc-
AVRDC and at BRCI. curred at soil depths of 10 to 20 cm and 20 to 30 cm.
From 10 to 50 kg ha
1
less of NO
3
–N was measured Chloride did not accumulate at the 30- to 50-cm depth
in planted than in unplanted plots between 3 and 8 wk in the raised beds.
after GM application in the DS at AVRDC (data not
shown). Nitrogen uptake by tomato or cabbage, mea-
Green Manure Nitrogen-15 Recovery in Soil
sured by the difference of NO
3
in the soil in planted
vs. unplanted plots, generally started 1 to 3 wk after Total soil C and N contents increased by about 5%
between the time of soybean incorporation and tomatotransplanting. Cabbage was apparently a strongerN sink
than tomato, for less soil NO
3
was found in cabbage harvest (Table 3). Although mobile humic acid (MHA)
C increased and calcium humate (CaHA) C and N de-than tomato plots. At MMSU, soil NO
3
–N contents in
early-transplanted tomato plots remained lower than in creased from the first to the second sampling, the effect
of GM application on these parameters is not cleareither later-transplanted plots or in the unplanted con-
trol plots (data not shown). No significant differences because these parameters changed similarly in the con-
trol plot between samplings.in soil NO
3
–N content between GM and control plots
were evident at the 30- to 60-cm soil depth at MMSU. The MHA and CaHA did not seem to be more active
in short-term N cycling than the bulk soil organic matterHowever, nitrate contents at the 30- to 60-cm soil depth
in GM treatments tended to be lower than the control (SOM), as the two fractions combined contained only
4.5% of the total soil
15
N in the soybean plot at tomatobefore GM application and higher than the control at
THO
¨NNISSEN ET AL.: LEGUME GREEN MANURES IN TROPICAL VEGETABLE PRODUCTION
257
Fig. 2. Nitrate contents in soil (0–30 cm) after application of green manure (soybean, indigofera at AVRDC, Taiwan, and at MMSU, Philippines;
soybean and mungbean at BRCI, Philippines) in raised (R) and low (L) beds, 1993–1995. Error bars indicate LSD (0.05); asterisk indicates
significance at the 0.1 probability level.
harvest. Most of the
15
N was recovered in the humin
DISCUSSION
(unextracted organic matter). Moreover, the ratios of
Factors Affecting Green Manure Decomposition
15
N to total N were similar for the MHA and CaHA as
and Mineralization
for the bulk soil, further suggesting that preferential
Decomposition rates of incorporated GM differed
accumulation of recently added
15
N did not occur in the
less between seasons and locations than for mulched
extracted MHA and CaHA. The MHA and CaHA had
GM. Incorporated residues are in a generally more fa-
comparable amounts of
15
N in the soybean plots at final
vorable environment for microbial decomposition (e.g.,
tomato harvest. Nitrogen-15 in total soil was not fully
close soil contact, adequate soil moisture, etc.) (Wilson
recovered in the MHA, CaHA, and humin, which may
and Hargrove, 1986). Fast initial decomposition of soy-
be due to losses of
15
N during extraction as fulvic acids.
bean in both seasons at AVRDC matches findings of
At tomato harvest, estimations of N losses were
greater calculated with
15
N than with total N (Table 4), Broder and Wagner (1988), where incorporated soy-
due to lower N recoveries of
15
N in both tomato and soil. bean residues lost 68% of their total biomass within 32 d.
Nitrogen-15 values for whole soils, MHA, and CaHA for In most comparisons, plant chemical composition ap-
all treatments except soybean at tomato harvest were peared to affect the decomposition rate of GM. Faster
too low to allow accurate measurement. decomposition of indigofera at AVRDC was probably
caused by its smaller and more tender leaves and less
Table 2. Percent remaining chloride at different soil depths for
three sampling dates in raised and low beds (AVRDC, Taiwan, Table 3. Organic C and N in total soil and in organic fractions
1993). Chloride was added on 23 June. (mobile humic acids [MHA]; calcium humates [CaHA] imme-
Sum
diately after (1 d) and 113 d after green manure application in
control and soybean incorporation plots. Standard deviation
Soil depth 0–10 10–20 20–30 0–30 30–40 40–50 0–50
of laboratory replicates of organic C and N contents of total
%Cl
soil are given in parentheses, 1994–1995, MMSU, Philippines.
Raised beds
Total soil
Organic matter fraction
21 Jun 78 46241 100 7 151 100
23 Jul 24 61216237514150 MHA CaHa
30 Aug 14 2925125313135
(d C N CNCN
Low beds
21 Jun 86 38361 100 gkg
1
soil
23 Jul 28 10 19 411258 1
30 Aug 23 116411250 Control 7.11 (0.01) 0.665 (0.01) 0.162 0.0163 0.448 0.0409
Soybean 7.04 (0.03) 0.707 (0.01) 0.218 0.0227 0.369 0.0346
Values shown are means of four treatments: control, Ck 120 kg N ha
1
,
soybean incorporation, and mulch, and standard deviation between treat- 113
ment means. Treatments means are means of four replicates. Control 6.85 (0.06) 0.669 (0.02) 0.212 0.0204 0.228 0.0243
† % Cl was calculated by setting the Cl contents (g Cl/m
3
) to 100% on 21 Soybean 7.39 (0.04) 0.750 (0.02) 0.240 0.0231 0.226 0.0248
June 1993 from 0 to 30 cm (raised and low beads), and additionally 0
to 50 cm for raised beds. † d, days after soybean GM application.
258
AGRONOMY JOURNAL, VOL. 92, MARCH–APRIL 2000
Table 4. Comparison of total N and
15
N balance after tomato
N-ratio (10.6) and higher initial N content (4.2%) of
harvest in soybean incorporation plots at MMSU, 1995. Values
indigofera may have determined its faster decomposi-
within parentheses indicate standard deviation (n3).
tion compared with soybean (C/N 12.2; N 3.9%). Results
Total N
15
N
of this study confirm the complexity of decomposition
kgNha
1
% recovery kg N ha
1
% recovery
processes where the interaction of both resource quality
and microclimate influence the conditions and activity
Input soybean 119.3 0.910
Output tomato 19.5† (10.8) 16.3 0.082 (0.02) 8.9
of decomposer communities and those in turn mediate
left soil 64.0 (20.0) 53.7 0.315 (0.01) 34.6
processes of decomposition and nutrient release (Neely
not found 35.8 30.0 0.513 56.5
et al., 1991; Hunt, 1977).
Calculated by subtracting tomato N in control from tomato N in soy-
High soil temperatures (20–30C) and moisture condi-
bean incorporation.
tions near optimum (0.01 to 0.05 MPa; Cassman
and Munns, 1980) were mainly responsible for the fast
release of NO
3
following GM application in all locationslignified stems relative to those of soybean. The slower
decomposition of incorporated soybean compared with and seasons. Nitrate-N release at AVRDC mirrored
the initial exponential loss of biomass, evidence for theindigofera at MMSU occurred despite similar plant
chemical compositions (data not shown). Sixty-day-old causal linkage between these two processes. Higher de-
composition rates of indigofera in the DS led to N re-soybean (maturity scale R5 to R6; Fehr et al., 1971) in
both seasons at AVRDC decomposed at rates similar lease in soil comparable to that of soybean, although
far less N (33 vs. 127 kg N ha
1
, Tho
¨nnissen Michel,to those of incorporated indigofera at MMSU. The phys-
ical nature of older soybean plant material (R6 to R7) 1996) was incorporated with indigofera GM. Reduced
mineralization rates of surface applied residues (mulch)used at MMSU, with hardy stems and pods containing
full size yellow beans, may have been one of the main can be attributed to poor soil–residue contact and dras-
tic temperature and moisture fluctuations at the soilreasons for the large differences in decomposition rates
between soybean decomposition at AVRDC and indi- surface (McCalla and Duley, 1943). Numerous authors
(e.g., Janzen and McGinn, 1991) have stressed the im-gofera at MMSU.
Many investigators have observed that organic resi- portance of volatilization losses when GM is applied as
surface mulch, since drying and decomposing conditionsdues decompose more slowly in soils with higher clay
contents, especially clays having higher exchange capac- enhance volatilization. The volatile loss of labile N from
decomposing GM mulch may appreciably diminish itsities (Lynch and Cotnoir, 1956; Sorensen, 1975). Micro-
bial activity is controlled by soil physical conditions such fertility benefit, whereas NH
3
losses from incorporated
GM have been reported to be negligible (Janzen andas compaction, temperature and oxygen; by chemical
conditions such as substrate availability; and by biologi- McGinn, 1991). If, however, lower mineralization rates
are the cause of reduced inorganic N accumulation un-cal conditions such as predatory or antagonistic organ-
isms (Grant et al., 1993). Reduced soil aeration or oxy- der no-tillage, then such a system could better conserve
organic N in the long term (Sarrantonio and Scott, 1988).gen in the clayey soil at MMSU compared with the
loamy soil at AVRDC may have further contributed to Slight increases in NO
3
contents in the soil 10 wk after
GM application in the WS at AVRDC and at BRCIa slower legume residue decomposition rate at MMSU.
The exponential weight loss pattern agrees with previ- (Fig. 2) may indicate remineralization of N that had
been immobilized earlier, even though the process isous assumptions that residues contain labile and recalci-
trant fractions having different degrees of resistance to considered to be relatively slow in temperate soils (Mary
and Recous, 1994). Lowest NO
3
–N contents in the soilmicrobial degradation. Reinertsen et al. (1984) associ-
ated the more rapid decay immediately after the burial with indigofera mulch were likely due to the NO
3
–N
uptake of the indigofera (Tho
¨nnissen Michel, 1996).of the residue with the decomposition of water-soluble
organic constituents. Hunt (1977) described differences Although N release dynamics may have been driven
by a combination of location and/or season-specific fac-in decomposition patterns and rates among substrates
as a function of the amount of the labile or rapidly tors, N release patterns across locations and seasons are
similar. High leaching and denitrification losses in thedecomposing fractions (sugars, starches, proteins) and
the recalcitrant or slowly decomposing fraction (cellu- WS at AVRDC may have reduced the amount of GM
N available to tomato plants, although temperature andlose, lignin, fats, tannins, waxes). Decomposition pro-
cesses can be predicted from initial litter chemistry soil moisture were more favorable for N mineralization
than in the DS. Results of an incubation study compar-(Aber et al., 1990; Neely et al., 1991). Seasonal effects
on chemical composition of legumes (i.e., C/N, initial ing N release after addition of dry organic residues to
these three soils (Tho
¨nnissen Michel, 1996) suggestedN, lignin, polyphenol, and tannin contents) have been
shown within the same location (Tho
¨nnissen Michel, that certain soil chemical and physical properties re-
tarded N release in MMSU soil, relative to BRCI and1996). The statistical significance of each chemical com-
ponent to the rate of GM degradation varied widely AVRDC soil. Soil basal N mineralization was higher in
the AVRDC and BRCI soils than in the MMSU soilbetween seasons and locations (Tho
¨nnissen Michel,
1996). The relatively high polyphenol (3.7%) and tannin (Tho
¨nnissen Michel, 1996). Significant amounts of inor-
ganic N were detected in fallow plots lacking GM addi-(1.6%) content of indigofera may have retarded decom-
position compared with soybean (polyphenol 1.7%, tan- tion prior to vegetable crops in the DS at AVRDC
and at BRCI, while leaching losses may have preventednin 0.2%) in the WS, whereas in the DS the lower C/
THO
¨NNISSEN ET AL.: LEGUME GREEN MANURES IN TROPICAL VEGETABLE PRODUCTION
259
nitrate accumulation in the WS at AVRDC. The higher
Total Nitrogen and Nitrogen-15 Balance
the soil N supply, the more legumes derive N from The similarities of the ratios of total
15
N to total N
soil rather than from biological N
2
fixation. Low NO
3
for MHA and CaHA fractions compared with humin
contents in legume plots can be explained by the effec- suggest that the two fractions were no more labile than
tiveness of legumes to assimilate NO
3
derived from soil the rest of the SOM in this soil. Our results are compara-
N mineralization (George et al., 1994; Ladha et al., ble to those of He et al. (1988), in that a significant
1996). proportion of recently added
15
N in the soil was not
At all locations and seasons, the decline of soil inor- extractable (humin). Humin can be very young and
ganic N at 6 to 8 wk after GM application may result much of it is composed of alkyl compounds and carbohy-
from a combination of the period of greatest N uptake drates as microbial byproducts (He et al., 1988). Domi-
by the tomato plants (Tho
¨nnissen Michel, 1996), lower nation of soil C and N by humin may be especially
rates of N mineralization (Griffiths et al., 1994) and pronounced in a soil where conditions are favorable for
biological N immobilization (Mary and Recous, 1994). degradation. The rapid decomposition of the soybean
The faster decline of soil nitrate in planted compared residues and the small quantities of MHA and CaHA
with unplanted plots suggests vegetable N uptake at extracted from the MMSU soil in relation to other rice
AVRDC and at MMSU. Using
15
N-labeled residues in soils of the Philippines (Olk et al., 1995) demonstrate
the absence of growing plants, Chotte et al. (1990) found the favorable conditions for degradation in this soil.
net immobilization in the organic residues, but net min- Organic molecules resulting from microbial degrada-
eralization occurred when plants were grown in these tion, such as microbial tissues, will be preserved in the
soils. Root exudates of vegetable crops may have been soil only if they are stabilized and thereby are protected
an insignificant energy source for soil microbial growth from further degradation. One such form of protection
(Martens, 1990) in our experiments because of the high is chemical binding to the mineral surface of such
degradability of our soybean and indigofera GM, and strength that the organic material is not extractable and
the favorable soil temperature and moisture conditions. hence considered as humin. The extremely high Ca lev-
Reduction of microbial activity and microbial N immo- els in MMSU soil may also contribute to the humin
bilization after consumption of the labile fractions of constituting a high proportion of total SOM.
the residue in early decomposition stages may have oc- Lower rates of
15
N recovery could be due to mineral-
curred due to the recalcitrance of the remaining crop ization–immobilization turnover. The
15
N released from
residue. It is possible that these recalcitrant organic frac- the legume residue into the soil inorganic pool could
tions lead to the formation of soil humus (Wilson and be exchanged for
14
N in microbial biomass, which could
Hargrove, 1986). If microbial N needs were large, avail- lead to lower
15
N recovery. Alternatively, lower rates
able soil inorganic N would be rapidly depleted and of
15
N recovery than total N may result partly from an
the decomposition rate of organic compounds would overestimation of apparent total N recovery and partly
decline (Mary and Recous, 1994), leading to N immobili- from the importance of soil conditions during the rapid
zation (6–8 wk) and delayed N remineralization. In ex- degradation of
15
N-labeled material. Higher mineraliza-
periments by Broadbent and Tyler (1962), NO
3
was tion rates of labeled than of unlabeled organic materials
immobilized to a considerable extent when it was the may have contributed to lower rates of N recovery in
only N form available to soil microorganisms. Mary and
15
N compared with total N balances, in agreement with
Recous (1994) described N immobilization–remin- other authors (Amato and Ladd, 1980; Chichester et
eralization following organic residue incorporation as a al., 1975). Greater loss of
15
N than total N (57 vs. 30%)
function of the amount and nature of the residues and may reflect volatilization and denitrification at the be-
soil mineral N, whereas basal mineralization was ex- ginning of the crop cycle, as well as the low plant N
plained as a function of soil texture and long-term C uptake at that time. Total N loss would be lower on a
and N inputs. percent basis during this time because of the low basal
It is probable that liming of the soil and the addition rate of SOM-N mineralization. Because labeled soybean
of poultry manure (Gallus sp.) led to a strong soil N was quickly decomposed, the fate of GM
15
N would be
mineralization in BRCI soil. Decay of plant residues disproportionately determined by soil conditions early
and SOM are accelerated by liming of acid soils (Alex- in the crop cycle. Given the relatively wet yet aerated
ander, 1977). conditions in the MMSU soil, these large amounts of
The great loss of Cl and ostensibly NO
3
within the
15
NH
4
mineralized quickly from plant residues or young
first month of GM and N fertilizer application in the
SOM fractions would be prone to losses via volatiliza-
WS at AVRDC, probably resulted from two rainfall
tion or nitrification–denitrification. This scenario is sup-
events within that period. The soil at 30 cm depth in
ported by the low total soil C and N levels, small quanti-
the raised bed system was permanently submerged due
ties of extracted MHA and CaHA, high losses of
15
N
to the standing water in the rice beds (Tho
¨nnissen Mi-
from the system, and the greater relative loss of
15
N than
chel, 1996), so that Cl may have been leached with rice
total N.
bed irrigation. Improved infiltration rate through soil
Given its low total C and N contents, the MMSU soil
in the raised beds may have also increased leaching
may not have a large capacity to store added N, whether
losses (Shennan, 1992). Our results confirm those of
the N is added in organic or inorganic forms. We con-
Stute and Posner (1995), that potentially leachable soil
NO
3
–N differed little following GM or N fertilizer. clude that the lack of synchronization between N supply
260
AGRONOMY JOURNAL, VOL. 92, MARCH–APRIL 2000
Ladha, J.K., D.K. Kundu, M.G. Angelo-Van Copenolle, M.B. Peoples,
and demand caused by a single application of GM
V.R. Carangal, and P.T. Dart. 1996. Legume productivity and soil
shortly before vegetable transplanting makes this treat-
nitrogen dynamics in lowland rice-based cropping systems. Soil Sci.
ment less successful than split applications of inorganic
Soc. Am. J. 60:182–192.
N (Tho
¨nnissen Michel, 1996).
Lynch, D.L., and L.J. Cotnoir, Jr. 1956. The influence of clay minerals
on the breakdown of certain organic substrates. Soil Biol. Bio-
chem. 20:367–370.
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... The variables percentage of decomposition and mineralized N of the field experiment, as well as biomass yield, concentration of N (%) and total N in the wheat biomass harvested in the experiment in pots, were subjected to an analysis of variance and comparison of averages using the Tukey test (0.05), the statistical program Statgraphics Centurión XVII (Statgraphics, 2014) was used. La rápida descomposición del AV en términos de pérdida de biomasa en las primeras semanas de incubación, así como una pérdida de peso lenta y gradual hasta el final del periodo de incubación es consistente con lo reportado por Thönnissen et al. (2000), los cuales mencionan pérdidas de peso del 30 al 70 % en Glicyne max e Indigofera tinctoria después de cinco semanas de incubación. En Brasil las especies Arachis pintoi, Calopogonium muconoides, Stizilobium aterrimum y Stylosantes guianensis fueron evaluadas como AV en plantaciones de café y se reportaron valores de pérdida samplings, the AV weight losses in the Regosol soil varied from 78.93 % in the flowering stage to 84.02 % in the vegetative stage. ...
... The rapid decomposition of VA in terms of biomass loss in the first weeks of incubation, as well as a slow and gradual weight loss until the end of the incubation period is consistent with that reported by Thönnissen et al. (2000), who mention weight losses of 30 to 70 % in Glicyne max and Indigofera tinctoria after five weeks of incubation. In Brazil, the species Arachis pintoi, Calopogonium muconoides, Stizilobium térimum and Stylosdamientos guianensis were evaluated as VA in coffee plantations and biomass loss values of 30 to 60 % were reported in the first 30 days (Matos et al., 2011). ...
... On the other hand, it is possible that the initial chemical composition of the VA, regardless of the phenological stage, was another factor that favored the rapid decomposition and mineralization of N, generally materials with a low C:N ratio and low lignin content (typical of many legumes) tend to decompose and mineralize faster than some organic substrates with high levels (Brunetto et al., 2011), therefore, high N contents in the C:N ratio and lignin limit the growth of decomposing microorganisms, for which is common the presence of recalcitrant compounds whose molecules present bonds more resistant to the degradation of organic materials (Brunetto et al., 2011;Odhiambo, 2010). In this regard, Thönnissen et al. (2000) mentioned that the weight loss pattern is consistent with previous assumptions that residues contain labile and recalcitrant fractions, which have different degrees of resistance to degradation microbial action. In this a descomponerse y mineralizarse más rápido que algunos sustratos orgánicos con niveles altos (Brunetto et al., 2011), por lo tanto, altos contenidos de N en la relación C:N y lignina limitan el crecimiento de los microorganismos descomponedores, por lo cual es común la presencia de compuestos recalcitrantes cuyas moléculas presentan enlaces más resistentes a la degradación de los materiales orgánicos (Brunetto et al., 2011;(Odhiambo, 2010). ...
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... Este efecto es considerado real si el desarrollo de las raíces y la eficiencia en la absorción fue mayor como resultado de la adición de una fuente nitrogenada, demostrándose la estrecha relación existente entre la mineralización del nitrógeno y su absorción por las plantas (Thönnissen et al. 2000). ...
... Overall, our study showed that the effects of GM residues containing Phi depended on soil type and GM species. Although lower decomposition rates of GM residues were expected in the clay soil (Midmore et al., 2000), no differences between soil types were observed. In fact, decomposition rate of GM residues was mainly influenced by the GM species (Table S1) likely as a result of physico-chemical properties of GM litter (Halvorson and Smith, 1995). ...
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Recycling phosphorus (P) is crucial to meet future P demand for crop production. We investigated the possibility to use calcium phosphite (Ca-Phi) waste, an industrial by-product, as P fertilizer following the oxidation of phosphite (Phi) to phosphate (Pi) during green manure (GM) cropping in order to target P nutrition of subsequent maize crop. In a greenhouse experiment, four GM crops were fertilized (38 kg P ha-1) with Ca-Phi, triple super phosphate (TSP) or without P (Control) in sandy and clay soils. The harvested GM biomass (containing Phi after Ca-Phi fertilization) was incorporated into the soil before maize sowing. Incorporation of GM residues containing Phi slowed down organic carbon mineralization in clay soil and mass loss of GM residues in sandy soil. Microbial enzymatic activities were affected by Ca-Phi and TSP fertilization at the end of maize crop whereas microbial biomass was similarly influenced by TSP and Ca-Phi in both soils. Compared to Control, Ca-Phi and TSP increased similarly the available P (up to 5 mg P kg-1) in sandy soil, whereas in clay soil available P increased only with Ca-Phi (up to 6 mg P kg-1), indicating that Phi oxidation occurred during GM crops. Accordingly, no Phi was found in maize biomass. However, P fertilization did not enhance aboveground maize productivity and P export, likely because soil available P was not limiting. Overall, our results indicate that Ca-Phi might be used as P source for a subsequent crop since Phi undergoes oxidation during the preliminary GM growth.
... In the literature, the results concerning the effects of residues on crop productivity are, however, divergent. Some studies have shown the immediate positive effect of the addition of crop residues on crop productivity [30,36,37]. However, many studies have shown that in the short term, the effects of the contribution of crop residues on crop productivity are low or even negative [38,39]. ...
... Previous 15 N-labelled soybean residue studies in the tropics have indicated the peak of N release occurs during 2-8 weeks after application, depending on residue placement, moisture and temperature (Thönnissen et al. 2000), and the N losses observed in our study over a 16-week period in the subtropics suggest similarly rapid mineralisation of N in soybean residues. Owing to the variation in %N in shoots (Table 1), the C : N in the three fields used for the isotope study ranged from 13 : 1 (field 9) to 16 : 1 (field 5), compared to 9 : 1 for the 15 N-labelled residue applied. ...
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... During mineralization of organic matter, a rapid release of K occurred and followed by slower releases of N, P and Ca [47]. However, the release of N, K and Ca is usually greater in legume litter due to tenderness of legume leaves compared to the slow release from grasses due to their higher lignification [48]. ...
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Chapter
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