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III. Biomass and Nitrogen Accumulation in Green Manures

III. Biomass and Nitrogen Accumulation in Green Manures

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waterlogged conditions and produced significantly less biomass than Sesbania and sunn hemp (Morris et al., 1986a). In California, Williams et al.

(1957) reported 0.9-1.4 t/ha dry matter yield of purple vetch. Dry matter

yield of subterranean clover ranged from 3.4-6.0 tlha (Dabney et al., 1989;

Hoyt and Hargrove, 1986).

Rainfall and temperature influence the biomass production of green leaf

manures. Gliricidia sepium shrub raised on the field boundaries produces

about 1-3 t dry leaf material per month from 10,000trees/ha. In India, G.

maculata was reported to produce about 14 kg green leaf per shrub in the

month of July, which could be used for green manuring the main season

rice crop. Sesbania speciosa planted during the month of August on the

boundaries of a hectare field (1 150 m) produced, within four months, an

average of about 42 t/ha of green matter for incorporation in the rice crop

transplanted in January. The seedlings planted in February on the boundaries during the second season gave about 4.0 t/ha green matter for the

main season rice crop transplanted in July (Vachhani and Murty, 1964).

In Sri Lanka, Weerakoon and Gunasekera (1985) showed that about

2.5 tlha leaf dry matter of Leucaena leucocephala could be obtained every

cropping season. S. sesban used as GLM gave total N yields of 32,46, and

47 kg Nlha in the first, second, and third year, respectively, of growth on

sodic soils in northern India, (Rao et al., 1989). In Thailand, S. sesban

produced leaf yields of 542-683 g/plant in wet season and 167-377 g/plant

in dry season, and was more productive than S.formosa and S . grandijiora

(Arunin et al., 1988).

Mukherjee and Agarwal (1950) and Ghai et al. (1985) reported that N

content of different green manures (8 weeks old) ranged from 1.5 to 4.85%.

Roger and Watanabe (1986)reported that N content in legumes varies from

0.2 to 0.6% (fresh weight basis). Ghai et al. (1985) and Hernandez et al.

(1957) observed that N content in Sesbania, sunn hemp, and T. candida

tops was maximum at 45 days of growth and decreased thereafter. In milk

vetch, N content before flowering was 4.5%, decreasing gradually to 3.2%

at the full-broom stage (Ishikawa, 1988). Morris et al. (1986a) observed

that different green manures showed a linear relationship between N

accumulation and dry weight irrespective of green manure species, and

were affected by the age of green manure crop. It was found that green

manures had maximum N content of 2.54% at 45 days and decreased to

1.88% in 60-day-old green manures.

N accumulation in the tops of several leguminous green manure crops is

shown in Table I. The values in excess of 100 kg N/ha are common for

45-50-day-old legumes. Hernandez et al. (1957) found that N yield of

45-day-old green manures ranged from 56-226 kg N/ha. Milk vetch and S.

cannabina in China fixed about 100-350 kg N/ha at full blooming. In the



United States, hairy vetch, crimson clover, subterrarean clover, and common vetch accumulated 56-209 kg N/ha, but in most cases it was between

100-150 kg N/ha (Smith et al., 1987). In Hawaii, Evans and Rotar (1987)

reported that high yielding accessions of annual Sesbunia produced 817 t/ha dry matter containing 150-245 kg N/ha when sown at 125,000

plantslha and harvested at 98 days after sowing. The highest yielding

varieties were related to S . cannuhinu, which are grown as green manures

in the Asian lowland rice system.

Like dry matter production, N accumulation is related to the age of the

green manure crop. Ishikawa (1963) reported that N yield of milk vetch

was 1.8 kgiha at the start of flowering, and increased to 156 kg Nlha during

flowering (14 days later). N accumulation of S. aculeata as related to its

age is shown in Fig. Ib. Palaniappan et ul. (1990) reported that at 45 days,

S. aculeata and S. rostrata in south India accumulated 185 and

219 kg N/ha, respectively. Chapman and Myers (1987) reported that soybean green manure at early flowering stage ( I 10 days old) fixed 124-167 kg

N/ha in different years. Evans et af. (1989) indicated that dry matter yield

varied from 2.0- 14.3 t/ha and

of narrow leaf lupin (Lupinus ~~iigustifalius)

total N in the shoot ranged from 45-267 kg N/ha. Mahler and Auld (1989)

studied the green manuring potential of Austrian winter peas (Pisurn

satiuurn aruense spp.) and reported mean biomass and N yield of 8.3 tlha

and 167 kg N/ha, respectively.

The contribution of roots to total N yield is generally small in most

leguminous green manures. In S. uculeafu,root dry matter averaged about

1.O t/ha, adding about only 10 kg N/ha at 50-60 days of growth (Morris et

ul., 1986a; Beri et al., 1989a; Meelu et ul., 1990). The root-to-top ratio of

milk vetch is about 0.05 and will supply only a negligible quantity for rice

production (Ishikawa, 1988). Westcott and Mikkelson (1988) reported that

sweet and crimson clovers have 24-26% of the entire crop biomass in the

roots, which contain 2.0-2.3% N; the tops contain 2.4-2.9% N. Vetch has

17-19% of the total biomass in the roots.

Using ''N isotope dilution technique, Chapman and Myers (1987) estimated that 60-72% of total plant N was from biological N2 fixation when

the legumes were grown after 12 months of fallow, and 93-95% when

grown immediately following dry season crop. Smith et al. (1987) concluded that N2 fixation values for legume cover crops ranged from

6 7 4 4 % . Using difference method, Meelu et al. (1990) observed that 80%

of the total N in the tops of 52-day-old S . uculeata was from biological N2

fixation. Similar estimates of N2 fixation have been made for S . rostrata

and S. cannabina by Pareek (1989) using different methods of evaluation.

In the past, only limited research has been directed toward enhancing

biological N2 fixation in the leguminous green manures. The important



approaches in this direction may involve: selection of superior plant and

rhizobium genotypes, including the consideration of plant-microbe interaction; refinement of inoculation technology; increased understanding of

rhizobium ecology; and improved management practices (Smith and

Knight, 1984). Alikhan et a f . (1983) developed a SSI selection of sunn

hemp which gave 37% increase in green matter yield and 70% increase in N

yield at 50 days of growth.






Application of inorganic fertilizers (N and P) and organic matter has

been reported to stimulate nodulation and Nz fixation by legume crops

(Gibson ef a f . , 1982). Phosphorus, which is required for efficient N2 fixation, is often a limiting nutrient in the tropical lowland soils. Results from

several studies have shown that P application increased biomass and N

accumulation of green manures (Table 11). The green manures generally

responded more to P application on soils low in available P and pH.

Venkatachalam et al. (1969) found that uptake of 32P by rice was greater

from P applied to the green manure crop than its direct application made in

four soil types. In China (Liu, 1988) and Japan (Ishikawa, 1988), application of P has been recommended for obtaining high biomass and N yield of

milk vetch. Beri and Meelu (1980) found that on a soil testing low in

available P, application of 13 kg P/ha increased biomass production and N

accumulation of S. aculeata green manure and gave better yield of rice

than P applied directly to rice. Many other research workers (Sanyasi

Raju, 1952; Sen and Rao, 1953; Desai et al., 1957; Singh and Verma, 1969;

Chen, 1988) have reported similar results.

On soils testing high in available P, application of P fertilizer did not

show any beneficial effect on biomass yield and N accumulation of green

manures (Relwani and Ganguly, 1959; Desai et a f . , 1957). Gu and Wen

(1981)reported that if available P content is below 15 mg/kg in the acid and

neutral soils or below 10 mg/kg in the calcareous soils, P application to the

green manures would be markedly efficient. The results of 311 experiments showed that application of 11-167 kg P/ha gave an average response


(1988) reported that

of 347 kg fresh biomass and 1.21 kg N/kg P ~ O SChen

while rice absorbed 66.2% of P applied to the green manure crop, it

absorbed only 14.7%of the P added directly just before transplanting.

The good effects of K fertilizer on the yield of green manure has been

found in some soils, and K can give effects similar to P on such soils (Chen,

1986). In China, Liu (1988) recommended application of K2S04/KCI at

75-105 kg/ha to milk vetch.

Table I1

Effect of P Application on Accumulation of Biomass and N of Green Manures




Sesbunia aculeata

S. aculeara

Sunn hemp

S. uculeara

S. rostrata

S . aculeara

N accumulation







soil P



P rate














6-3 1


























1. Singh el nl. (1968); 2, Beri and Meelu (1981); 3. Sharma and Mittra (1988); 4, Herrera e r a l . (1989); 5, Singh (1990).

g/6 plants.

















Rational application of N fertilizer can also increase the N2 fixation rate

of a green manure crop. At low level of N, a starter dose of N was found to

promote nodulation and N2 fixation by legume crops (Gibson et al., 1982).

Gu and Wen (1981) reported that 1 kg of fertilizer N could increase

1.7 0.9 kg N in the green manures. Chapman and Myers (1987) found

that application of a starter N dose (25 kg/ha as urea) increased 10 and 30%

N in the tops of Sesbania and soybean at the flowering stage in the first

year of study. Sharma and Mittra (1988) observed that application of 15 kg

N/ha as urea increased N accumulation of sunn hemp and Sesbania by 23

and 30 kg/ha, respectively. Application of 25.5 kg N/haat the stem elongation stage gave a three- to 4-fold increase in fresh biomass of milk vetch

over its application at the seedling stage. The plant recovery of fertilizer N

applied at the seedling stage was 32%, and that applied at the stem elongation stage was about 78% (Gu and Wen, 1981).

Soil organic matter can affect growth and survival of rhizobia in soil.

Application of 7.5 t/ha of farmyard and poultry manure enhanced root

nodulation of soybean and increased N2 fixation by 209% and 149%,

respectively, over unamended treatments (Dev and Tilak, 1986). In

Thailand, Herrera et al. (1989) observed that application of small rates of

farmyard manure (3 t/ha) was slightly more advantageous when applied to

S. rostrata rather than to rice.



Inoculation enhances the onset and number of effective nodules and N2

fixation by legumes. Ishikawa (1988) observed that inoculation of milk

vetch seed with rhizobia before sowing increased green matter production

by more than 3 times than without inoculation during the first year. In

subsequent years the increase was about 48%. Chu (1954) reported that

inoculation of soybean seed used for green manuring can help increase rice

yields by 20.7% over no inoculation.

Ladha et al. (1989) reported that both stem and soil + seed + stem

inoculation methods produced significantly more nodules (stem and roots)

and biomass of stem-nodulating legumes ( S . rostrata) than did the control.

The plants that were not inoculated on the stem did not develop stem

nodules. Alazard and Duhoux (1987) reported that plant dry weight of

9-week-old A . afraspera was 8.0 g/plant when only roots were inoculated

but it increased to 46 g/plant when both stem and roots were inoculated.

The corresponding values for N accumulation were 158 and 366 mg/plant.

Arunin et al. (1988) reported that inoculation of S . rostrata with improved strains of ORS 571 markedly increased (34-50%) its dry matter



(plant weight + pod weight) under both flooded and upland conditions.

The improved strain was more effective than native strain. In S. cannabina, S. speciosa, and S . uculeatu inoculation helped to improve their

growth (29-242%) under flooded conditions only. In Sri Lanka, Kulasooriya and Samarakoon (1990) reported that decapitation and stem inoculation of S . rostratu increased dry weight/plant by more than two times and

N yield by about three times over the control.


Singh and Lamba (197 1) recommended that cowpea should be irrigated

when the available water in the 180-cm profile is depleted by 35%. Gaul et

al. (1976) reported that during summer in northern India, about 600650 mm of irrigation water would be required for raising a 74-day-old green

manure crop of S . aculeata on alkali soil. N . T. Singh et al. (1981) found

that irrigation frequency (irrigation water/pan evaporation = 0.5- 1 .O) exerted a significant influence on the dry matter and N yields of 7-week-old

green manure crops of S. aculeata, cowpea, and clusterbean in semiarid

regions of Punjab, India. In China, Gu and Wen (1981) reported that for

optimum yield of milk vetch, surface soil moisture (0-10 cm) should be

maintained at about 70% of water-holding capacity until winter in order to

speed up the root growth.



Traditionally, green manures were grown in fallow fields on rainwater

and incorporated 2 to 4 weeks before sowing of the following crop. This

practice is, however, not feasible in the context of intensive agriculture

when there is a fallow period of only 40-60 days before transplanting of

rice. While studying the possibility of green manuring in the present-day

rice-based cropping systems, Bhardwaj (1982), Ghai et al. (1988), and Beri

et al. (1989b) showed, on the basis of yield responses, that a 2-week delay

between incorporation of green manure and transplanting of rice was not

only unnecessary but also disadvantageous (Table 111). In fact, Williams

and Finfrock (1962) and Vachhani and Murty (1964) had already demonstrated that green manure could be incorporated even at the time of

transplanting rice seedlings. The reason for low efficiency of green manure

when incorporated for a longer period before transplanting rice or flooding



Table 111

Effect of Interval between Incorporation of Green Manure and

Rice Transplanting on Rice Yield (t/ha)







Beri et al.












0- 1








Ghai et al.



could be the loss of green manure N released during aerobic decomposition through ammonia volatilization, nitrification-denitrification, and

leaching after flooding of rice fields (Ishikawa, 1988; Chapman and Myers,

1987; Williams and Finfrock, 1962). Ishikawa (1963) observed that with

simultaneous flooding and milk vetch incorporation, loss of N through

apparent denitrification was small. When flooding began 10 days after

application, milk vetch decomposed rapidly under 10-day aerobic conditions and NH4+-N was converted to N03--N, which was lost upon flooding, possibly through denitrification.

A few investigations have shown that it is not always necessary to

incorporate green manure a day or two before transplanting rice (Iso, 1954;

Staker, 1958; Roy et al., 1988; Tiwari et al., 1980; Rana et al., 1988).

Swamp (1987) showed in field experiments that allowing decomposition of

Sesbania green manure for 1 week under flooded conditions in sodic soils

significantly improved rice yields over simultaneous incorporation and

transplanting of rice, possibly through improvement of physicochemical

properties of sodic soils. Wen (1984)and Herrera et al. (1989) reported that

it is better to turn under green manure crop about 15 days before transplanting rice seedlings so that plants do not suffer damage from the decomposition products of the green manure. To avoid losses of green manure N

it was recommended to keep the fields flooded during the decomposition

period before transplanting rice.

Ishikawa (1988) concluded that only in poorly drained fields with low

rates of nitrification was rice yield not influenced by flooding time in

relation to application of milk vetch green manure. Soil moisture conditions during the preflooding period significantly influenced the effectiveness of green manure (Williams and Finfrock, 1962). Under conditions

favorable to nitrification during the preflooding period, the shorter the

period, the greater the effectiveness.

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III. Biomass and Nitrogen Accumulation in Green Manures

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