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VI. Nitrogen from Green Manure Crops

VI. Nitrogen from Green Manure Crops

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159



GREEN MANURING IN WETLAND RICE



Table V

Nitrogen Fertilizer Equivalence (NFE) of Green Manures

~~



Green manure

crop

Purple vetch

Crotolaria quinyuifolia

Sesbania aculeata

S. aculeata

S. aculeata

S. aculeaia

Sunn hemp

S.rostrata

S.cannabina

S. rostrata

Milk vetch

Mung beanlcowpea

Aeschynomene afrasperal

A. nilotica

S. rostrata

S. aculeata

S.aculeatalsunn hemp

Milk vetch



S. sesbarz

S. aculeata

Sunn hemp

S. aculeatalsunn hemp1

cowpea

S. cannabinalcowpeal

sunn hemp

S. cannabina

S. rostratalsunn hemp

S. acirleuta

S . aculeata



Age"

(days)



NFE

(kglha)



Reference



Sep- Apr

I05

67

50

50

50

52

45-65

55



27-49

23

57

78

98- 147

131



34

100

34

80

80

50

75

130

100-120

80



40-45

49



90

74-86

-



90

80

>loo



Rinaudo et ul. (1983)

Bhardwaj and Dev (1985)

Crozat and Sangchyosawat

( 1985)

Jiao et al. (1986)

Morris et a/. (l986a)

Alazard and Becker (1987)



50

45

F

23.4 tlha

(GM)

84

56

56

60



I09



70

123

40-60

94



Ventura et al. (1987)

Ghai et a/. (1988)

Roy et al. (1988)

Ishikawa (1988)



-



-



Williams et al. (1957)

Ten Have (1959)

Vachhani and Murty (1964)

Dargan et al. (1975)

Tiwari et al. (1980)

Bhardwaj et al. (1981)



83

108-1 13



96

45

60

120



Palm et ul. (1988)

Sharma and Mittra (1988)



60



-



50- 105



O.P. Meelu (unpublished



48



70

45-75

97- I 50

41-70

121

55-80



80

70

90

72

136

72

148

98



-



60

-



S.aculeata



-



Sunn hemp

Sunn hemp

Cowpea



-



"



Green

manure

N (kglha)



-



Beri et a/. (1989a,b)



data)

Morris et al. (1989)

Rabindra et al. (1989)

Shukla et al. (1989)

Y . Singh er a / . (1990)



F, flowering; GM, green matter.



falls between 25 and 50% in maize as compared to about 100% in rice

(Table V). Krishna Rao et al. (1961) and Jiao et al. (1986) have reported

that green manure N was as effective as fertilizer N when added on equal

N basis. Anti1 er 01. (1988) computed optimum N rates for wetland rice

as 152, 74, and 66 kg Niha after fallow, S . aculeata, and sunn hemp, re-



160



YADVINDER SINGH E T A L .



spectively. Like fertilizer N , application of green manure N in excess

of that needed for the highest rice yields could result in its poor efficiency

(Bhardwaj, 1982; Bhardwaj and Dev, 1985; Morris er al., 1989).

B. N TRANSFER

FROM GREEN

MANURE

TO RICE

Similar to fertilizer N , the recovery of green manure N will vary considerably with soil type, management, and weather. Working on a clay soil

and using I5N labeled vetch green manure, Westcott and Mikkelsen (1987)

recorded 10% N recovery of added vetch N (60-120 kg N/ha). Recovery

was 16-25% with ammonium sulphate added on an equivalent N basis.

Apparent N recovery was also lower with vetch N (9-26%) than with

ammonium sulphate (19-53%). They observed that when conditions inhibited the early season mineralization of green manure N , recovery rates of

green manure N would not compare favorably with that of fertilizer N.

Contrarily, Williams and Finfrock (1962) working on different soils and

rice cultivars found apparent vetch N recovery rates as high as 103%.

Chapman and Myers ( 1987) indicated that inefficient management of green

manure resulted in its low efficiency in flooded rice. Apparent green

manure N recoveries have been reported to vary from 25 to 58% (Table

VI). Generally, recoveries of N from green manure were similar to those

from fertilizer.



USEOF GREENMANURE

A N D FERTILIZER

N

C. INTEGRATED

The amount of N accumulated by different green manures is not likely to

be able to provide the levels of N currently required by the high yielding

rice cultivars (Talley and Rains, 1982). Therefore, to achieve the yield

potential it often needs to be supplemented with inorganic fertilizers.

Supplementing basally applied green manure with top dressed fertilizer N

helps in maximizing both green manure and fertilizer N recovery (Morris

et al., 1986a,b). In situations where green manure N is sufficiently high, it

may be advisable to cover more area to green manuring so as to get

increased rice yields. This practice will also help avoid crop injury caused

by excess application of green manure.

Several workers (Beri and Meelu, 1981; Nagarajah and Nizar, 1982;

Rekhi and Meelu, 1983; Khind et al., 1985; Joseph, 1986; Rana et al., 1988;

Mahapatra and Sharma, 1989; Kalidurai and Kannaiyan, 1990) have reported that green manure plus 50% of the recommended fertilizer N resulted in higher rice yields than when recommended N rates were applied.



161



GREEN MANURING IN WETLAND RICE

Table V1

Recovery of Green Manure N by Rice under Different Soil and Climatic Conditions

N recovery (95)



Green manure

crop



GM



Fertilizer



Reference



Appurent N recovery



Mung beanicowpea

Arschynomenr ufrusprral

A . nilotrca



S.aculeatu

S. aculeata

Cowpea

S. rostruto

Sunn hemp

S . rostrata

s. aculrata



33-49

25-35



33-49

25



Morris el a / . (1986b)

Alazard and Becker (1987)



44

42

2 1-29

41

34

34-51"

58



38

50

25-43

34

34

61



Ghai et al. (1988)

Y.Singh et al. (1988)

John et a/. ( 1 9 8 9 ~ )

Rabindra et a / . (1989)

Ladha rt al. (1989)

Shukla rt a / . (1989)



" N rrcouerv



Milk vetch

Seshania sp.



Sunn hemp

Milk vetch

Milk vetch

S . uculeata

"



"



25"

30-34

34-4s

38

30

32



5 1-64

57-60

25

51



Gu and Wen (1981)

H u a n g e t a l . (1981)

Liu (1981)

Mo and Qian (1983)

Biswas (1988)



Pot study.

Mean of 10 experiments.



Tiwari et ul. (1980) reported that green manure plus 40 kg fertilizer N/ha

produced rice yield comparable with 120 fertilizer N/ha alone. Ishikawa

(1988) reported that combining green manure and fertilizer N (56 : 38)

resulted in greater rice yields than from fertilizer N alone. Rabindra ef u l .

(1989) showed that application of a part of N (30%) through green manure

produced significantly more rice yield and N uptake than from 100 kg urea

N/ha alone. In most of the studies, rice yield potential was high when

green manure and an optimum quantity of fertilizer N were applied toget her.

Since a major fraction of green manure N is released and becomes

available to the rice plant within 2 to 3 weeks of its incorporation, the N

requirement of rice in the early growth period could be met by green

manure. Thus, Desai et al. (1957) observed that in rice green manured with

sunn hemp, top dressing of fertilizer N after first weeding (25-30 DT)

produced significantly higher yield (10%) than its application at transplant-



162



YADVINDER SINGH ET AL.



ing. Meelu and Morris (1988) showed that N applied with green manure in a

single dose at panicle initiation growth stage increased rice yield more than

the split-applied N . Results of field experiments conducted on a coarsetextured soil showed that Sesbania N was sufficient for the wetland rice at

the early growth stages, and application of fertilizer N at transplanting

could be delayed without any adverse effects on rice yield (Khind et af.,

1987b; Singh et al., 1987). Biswas (1988) reported that application of 30 kg

Nlha as urea 5-7 days before panicle initiation with basal incorporation of

Sesbania green manure improved grain yield, N uptake, and agronomic

efficiency. There is an obvious need to work out precise rate and time of

fertilizer N application to rice grown on fields amended with green manure

under different soil and climatic conditions.



VII. TRANSFORMATIONS OF GREEN MANURE NITROGEN IN

WETLAND RICE SOILS

The fate and availability of N in green manures are determined by the

rate and extent of manure decomposition and associated N mineralization.

The composition of green manure affects the overall mineralization rate.

The stem and roots of green manure are generally poorer in N content and

have wider CIN ratios than that of foliage portion (Palm et a f . , 1988).

These parts decompose slowly and could result in immobilization of N.

The net N release from green manure is the balance of all the N transformation processes occurring in the different parts of green manure. The

efficiency of green manure N should depend on the extent of N losses,

and the rate of N supply to the growing crops through mineralizationimmobilization turnover rate.

A. N MINERALIZATION

FROM GREENMANURES

Release of mineral N from green manure is initially rapid, but slows

markedly within a fairly short time (P. K. Singh et al., 1981; Khind et af.,

1985; Y . Singh et al., 1988; Bhardwaj and Dev, 1985). This behavior is

typical of most organic amendments (Van Faassen and Smilde, 1985). In

the absence of rice plants, N release increased rapidly up to 2 weeks and

reached a plateau (Aspiras, 1966; Nagarajah, 1988; Nagarajah et af., 1989)

(Fig. 3). In the presence of rice plants, soil solution NHd+-N peaked at 2-4

weeks after green manure addition and then declined to low levels at 6-12

weeks (Fig. 3). The decline was attributed largely to plant uptake. The time



GREEN MANURING IN WETLAND RICE



I63



DAYS AFTER TRANSPLANTING



FIG.3. Effect of Sesbania green manure on exchangeable NH4+ N in a field (a) without

rice crop and (b) with rice crop. (Adapted from Nagarajah, 1988.)



of occurrence of peak of mineral N released from green manure varied

greatly in different studies. It should not be surprising keeping in view the

effect of plant composition and environmental factors on rate of N release.

In some studies conducted in the absence of rice plant, a decline in

NH4+-Nafter a peak has been observed (P. K. Singh et al., 1981; Bhardwaj and Dev, 1985; Khind et al., 1987b; Beri et al., 1989b). It could be due

to losses of N via nitrification-denitrification and volatilization as NH3.

The simplest model representative of the N mineralization kinetics of

organic substrates added to soil is the mathematical formulation for the

first-order kinetics. Frankenberger and Abdelmagid (1985) found first order N mineralization rate constants for the legume residues incubated at

field capacity moisture regime to range from 0.045 to 0.325Iweek. Bouldin

(1988) proposed a simple two-component model to describe the N mineralization pattern of green manures. The organic material is treated as if there

are two distinct components-one decomposes rapidly, the other slowly.

It was proposed that 65% of the added N mineralizes during the first crop,

14% mineralizes during the second crop, and 3.3% mineralizes during each

succeeding crop. Recent work of Y. Singh rt al. (1988) indicated that N

mineralization kinetics of green manure could be described by two simultaneous first-order reactions: an initial fast reaction ( k = 2.12/week)

followed by a slow release of inorganic N ( k = 0.069Iweek). Gale and

Gilmour (1988) studied C and N mineralization from alfalfa as a threephase process. Under anaerobic conditions, the rate constant for slow

phase was near zero, and for rapid and intermediate phases these were

0.118 and 0.024/day, respectively. Gilmour et al. (1985)confirmed that the

amount of net N mineralized was related to net C mineralization.

There have been few studies on decomposition and N mineralization of

green manures under waterlogged conditions. And in some of the studies

inconclusive results have been obtained due to simultaneous loss of miner-



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