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The nitrogen (N) dynamics of nine rotation systems designed to transition dryland cereal to organic production in eastern Washington State were examined. Systems combined cereal and legumes for grain, forage (FOR), and green manure (GRM). Few differences in N balances and soil inorganic N levels were found among transition systems when poor spring crop establishment resulted in competition from weeds. However, FOR and winter GRM crops produced adequate stands that were competitive with weeds and increased residual soil inorganic N in the final year of the transition. Winter legumes and continuous FOR systems demonstrated the greatest potential to provide a sustainable inorganic N source to subsequent organic cereal crops. [ABSTRACT FROM PUBLISHER]

Field experiments were carried out in Central Italy on several green manure species (pure or mixed) and on succeeding grain maize to find practical relationships for predicting the N effect (N absorbed by maize that derives from the actual gain in soil available N due to green manure). Actually, little information is available for Mediterranean environments, where green manure species and strategies may be other than those of northern-temperate and tropical regions. Relationships were found for maize shooting (Neff = -3.61DW + 29.75N%; R2 = 0.67), flowering (Neff = -1.32DW + 27.47N%; R2 = 0.66) and physiological maturity (Neff = -4.84DW + 50.43N%; R2 = 0.74) (DW = incorporated biomass, N% = N concentration). [ABSTRACT FROM AUTHOR]

A field experiment was conducted for three years to compare farmyard manure (FYM) with legume and non-legume green manures at different levels of fertilizer nitrogen in potato (Solanum tuberosum)-sunflower (Helianthus annuus) sequence. Farmyard manure and green manures [sesbania (Sesbania aculeata), pearl millet (Pennisetum typhoidium) and sesbania+pearl millet] were incorporated before planting of potato crop. Five levels of fertilizer N, i.e., 0 (N0), 60 (N1), 120 (N2), 180 (N3) and 240 kg N ha-1 (N4) were applied to potato. Residual effect of organic manures was studied on following sunflower at three levels of fertilizer N (0, 30 and 60 kg N ha-1). Incorporation of inorganic manures improved organic C, available P and available K content in soil after three years in potato-sunflower sequence. Among the various organic manures, the highest potato tuber yield was recorded in FYM treatment. The response to N application was observed up to 180 kg N ha-1 irrespective of organic manure treatment. The contribution of larger size (>4.5 cm) potato tubers towards yield increased with fertilizer N and was 13.0, 17.9, 23.1, 24.4 and 26.7 percent with N0, N1, N2, N3 and N4 at 90 days after planting (DAP). However, the contribution of smaller size tubers (<3.5 cm) was in the order of N0 > N, > N2 > N3 > N4. The percentage contribution of larger size tubers towards yield was more in FYM plots than other organic manures. The increase in N uptake with organic manures over non-manured treatment was 51.6, 27.8, 27.1 and 6.2 percent with FYM, sesbania, sesbania + pearl millet and pearl millet, respectively. Organic manures had significant residual effect on seed yield, growth and phenology of sunflower, the response to FYM being more than green manures. Fertilizer N application up to 60 kg ha-1 to sunflower also improved seed yield, plant growth and prolonged grain filling period. [ABSTRACT FROM AUTHOR]

An on-farm study to evaluate three methods of applying legume residues in maize-based cropping systems in the central Kenya highlands was initiated in 1997 and conducted for three years. The legumes involved in the study were velvet bean (Mucuna pruriens (L.) DC) and crotalaria (Crotalaria ochroleuca G. Don), which were planted between maize (Zea mays L.) rows, two weeks after planting maize. The legumes were left growing in the field after maize harvest, until land preparation for the next maize crop. The legume forage was harvested and was either incorporated into the soil, left on the surface as mulch, or removed from the field before planting maize. The first cropping season when green manure legumes were establishing, maize grain yields were depressed by an average of 33% compared to the non legume control treatment. The legume treatments increased maize grain yields from a mean of 1.0 t ha⁻ⁱ in the controls to a mean of 1.6 t ha⁻ⁱ during the 1998 and 1999 long rains cropping seasons. Over the two cropping seasons, incorporation of legume residue into the soil gave a higher maize yield (2.1 t ha⁻ⁱ) compared to leaving the legume biomass on the surface as mulch (1.4 t ha⁻ⁱ). The effects of below-ground biomass on maize yields were minimal. The legume treatments did not significantly affect soil N, P, K, and organic carbon. During the study, farmers were able to identify characteristics of suitable green manure legumes and also identify possible niches for green manure legume technologies. [ABSTRACT FROM AUTHOR]

Integrating fertilizer nitrogen (FN) with legume green manure (GM) could lead to sustainable and environmentally sound agricultural systems in subtropical-semiarid soils low in organic matter. A six-year replicated field experiment was conducted on a semiarid irrigated Tolewal sandy loam soil (Typic Ustochrepts) in northwest India. The purpose of the experiment was to evaluate the direct and residual effects and cost effectiveness of cowpea (Vigna unguiculata L.) grown as a GM-crop in situ for 45-50 days during either the hot-dry period (May-June) prior to transplanting of rice (Oryza sativa L.) or the mildrainy season (September-October) prior to seeding of rapeseed (Brassica napus L.) in rice-rapeseed double cropping annual rotations. Rice grain yields with incorporation of 20 t GM ha-1(GM20)ranged from 3.93 to 5.28 t ha-1, which were 48 to 78% greater than the no-N control. Rice yield with 60 kg FN ha-1(FN60) and GM20 was more than double the control yield and 24% greater than the otherwise optimum rate of 120 kg FN ha-1. Incorporation of 20 t GM ha-1 to rapeseed produced 28 to 50% greater yields than the control. Combined application of GM20 with 100 kg FN ha-1 (recommended N rate in this region) further improved the yield potential of rapeseed by 16%. While FN had no residual effects, residual GM produced 9 and 35% greater yields of a succeeding crop due to the supply of N equivalent to 17 and 44 kg FN ha-1 in rice-applied and rapeseed-applied GM, respectively. Nitrogen utilization by the rice-rapeseed system was greater for GM20 than FN, as indicated by greater apparent N recovery by crops of 67% versus 51%. These results suggest that (a) green manuring in rice-rapeseed production systems is cost effective, and (b) under constrained water resources, GM produced during the mild-rainy season and applied to rapeseed is more beneficial than rice-applied GM. [ABSTRACT FROM PUBLISHER]

This investigation was part of a project to evaluate green manure forage legumes as relay intercrops for sweet corn (Zea mays L.) and chile (Capsicum annuum L.) in north-central New Mexico. The study was carried out under irrigated conditions in 1994 on a Fruitland sandy loam (coarse-loamy, mixed, calcareous, mesic Typic Torriorthent) to evaluate the 15N recovery by forage sorghum (Sorghum bicolor L.] Moench) and soil after the incorporation of lSN-labeled alfalfa Medicago sativa L. Nitro') or hairy vetch (Vicia villosa Roth. 'Madison'). Two application rates of alfalfa (2.7 or 4.0 Mg dry matter ha[sup -1]) or hairy vetch herbage (3.2 or 6.4 Mg dry matter ha[sup -1]), were incorporated into soil microplots. Additional treatments consisting of 56, 112, and 168 kg N ha[sup -1] (as urea) were used to compare soil inorganic N concentrations with those released from the legumes. Nitrogen-15 recovery by sorghum tops was 16% of the [sup 15]N applied, in two harvests. Of this, 80% was recovered at the first harvest. In soil, [sup 15]N recoveries were 50 and 3% of the input at the 0-0.3 and 0.3-0.6 m depths, respectively. Maximum inorganic N concentrations were found 14 d after amendment application. At the end of the growing season, inorganic N concentrations in all treatments were essentially the same as the background (8 mg N kg[sup -1]). The low [sup 15]N recoveries by crop plus soil and inorganic N concentrations in soil at the end of the season suggest that about 12% and 35-58% of the N applied as green manure was lost from the system for alfalfa and hairy vetch, respectively. [ABSTRACT FROM AUTHOR]

Forage legumes in crop rotations are often used to supply N for succeeding crops. However, the residual effect of forage legume green manures for second crops has not been thoroughly investigated in high desert regions of the Southwestern United States. The objective of this study was to evaluate the [sup 15]N recovery by a second subsequent crop (oat [Avena sativa L.]) and soil from microplots amended with [sup 15]N-labeled alfalfa (Medicago sativa L. 'Nitro') and hairy vetch (Vicia villosa Roth 'Madison'). In 1994, two application rates of each legume were incorporated into 1 m² microplots and forage sorghum (Sorghum bicolor [L.] Moench) was used to evaluate the [sup 15]N recovery. Aboveground residues were removed from microplots immediately after each of the two sorghum harvests. In 1995, the [sup 15]N recovery by the oat crop was determined. Nitrogen-15 recovery by oat averaged 3% of applied as green manure. Of this, 95% was found in tops and 5% in roots. Averaged across application rates, oat recovery of [sup 15]N was 63% greater in treatments amended with alfalfa than with hairy vetch. Green manures did not affect the total N concentration of oat parts. Most of the residual [sup 15]N was found in soil at the 0-0.3 m depth at the end of the oat season. The percent of [sup 15]N recovery by soil in plots amended with alfalfa was 238% higher than with hairy vetch. Green manures applied in 1994 had little residual effect on the N nutrition of oat. [ABSTRACT FROM AUTHOR]

Declining soil fertility and limited quantity and quality of livestock feeds are major constraints to agricultural production in northwestern Kenya. Legumes used as green manures may aid in overcoming soil nutrient depletion and lack of fodder. Relay-cropped mucuna (Mucuna pruriens (L.) DC. var. Utilis (Wright) Bruck) and lablab (Lablab purpureus (L.) Sweet cv. Rongai) were evaluated as alternatives to dry season, natural fallow for sustaining soil productivity in a maize (Zea mays L.)-common bean (Phaseolus vulgaris L.) intercrop on farmers' fields in northwestern Kenya. Four treatments were the factorial combinations of the two legumes and two levels of legume defoliation (none, or herbage above 10 cm removed prior to incorporation of remainder). Three controls were cattle manure (5 Mg ha-1), inorganic N (30 kg ha-1), and natural fallow. Undefoliated mucuna (UD-M) yielded more biomass (2.3 Mg ha-1, mean of two seasons) than undefoliated lablab (UD-L; 0.8 Mg ha-1) under the relay intercrop, contributing more nutrients to succeeding maize than lablab. Defoliation of the legume green manures removed on average 0.9 Mg ha-1 yr-1 of high quality top-canopy herbage. Nitrogen contribution ranged from 6 kg ha-1 for defoliated lablab (D-L) to 65 kg ha-1 for UD-M. Maize grain yield was greater (P = 0.003) following incorporation of mucuna vs. lablab in both seasons. Defoliation of legume residues prior to incorporation decreased subsequent maize grain yield (3.19 vs. 2.49 Mg hat following mucuna; 2.28 vs. 1.92 Mg ha-1 following lablab). Relative to the natural fallow control, UD-M, defoliated mucuna (D-M), and UD-L resulted in 52, 34, and 14% increases in subsequent maize grain yield. In conclusion, relay cropping green manure legumes, particularly mucuna, has potential to increase subsequent maize grain yield even when some of the fodder is used as livestock feed. [ABSTRACT FROM AUTHOR]