In a 3-year field study, the effects of substitution of nitrogen requirement of maize through Leucaena leaves were studied on runoff, soil loss, maize and wheat yield and economic returns. The treatments were (1) 80 kg N ha -1 all through Leucaena leaves (80 L), (2) 40 kg N through Leucaena leaves + 40 kg N ha -1 through fertilizer (40 L + 40 F), (3) 20 kg N through Leucaena leaves + 60 kg N ha -1 through fertilizer (20 L + 60 F), (4) 80 kg N ha -1 all through fertilizer (80 F), and (5) control (No fertilizer). Green Leucaena leaf biomass (containing 3.3% N on dry basis) was incorporated every year in 15 cm top soil two weeks before sowing of summer maize.
Some conservation based agroforestry systems (AFS) were developed for possible adoption in place of high risk rainfed farming on land capability classes I to 1V of a typical topo-sequence of foothill north India. The agri-silvi-horticulture system integrating leucaena, lemon, papaya and turmeric on class I irrigated land provided sustainable mean net returns of Rs. 17066 against Rs. 7852 ha. -~ yr. -a from double cropped agricultural system. The intercropping of cluster beans with leucaena gave the highest net returns of Rs. 3540 ha. -a yr. -1 in the agri-silvicultural system adopted on class II land. Eucalyptus tereticornis (Smith) in top and Bhabbar grass (Eulaliopsis binata Retz) in the understorey on a sandy loam class 11I land gave four years (1985-1988) mean air dry grass yield of 4.2 (used for paper pulp) from October mad 1.19 t. ha -~ yr. -a (used for fodder) from June cut. The net returns from grass alone were Rs. 4672 against Rs. 1679 ha. -1 yr. -~ from rainfed field crops raised on an adjoining plot. The returns from trees would be additional. Bhabbar grass raised under Acacia species on a 25 to 30% sloping gravelly class IV land provided yield varying from 2.18 to 4.31 from October cut and 0.50 to 1.1 t. ha. -a yr. -~ from June cut with 6 years mean of 3.9 t. ha. -~ yr. -a which at 1988 prices provided net returns of Rs. 2402 ha-L These AFS proved superior to traditional farming on each land capability class.
In an attempt to predict wet/dry spell and weather cycle, Markov chain model was fitted to the daily rainfall data (1958 to 1980) of Chandigarh. Conditional probabilities for occurrence of wet day preceded by wet/dry day were calculated and the expected frequencies of wet and dry spell and the weather cycle have been worked out with the help of the model. The study on the basis of X2 test has revealed the expected frequencies to fall in agreement with the observed ones.
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