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N but also enhance the availability of P thus enhancing the yield of dryland crops
(Snapp and Silim 2002 ). The net profit from maize crop were enhanced by 50 %
when synthetic fertilizer was used in a maize-legume intercrop or crop after a grain
legume in rotation than the continuous crop of maize (Waddington and Karigwindi
2001 ). In a 4-year study in West Africa (Zimbabwe), the overall grain yield was the
maximum for millet-groundnut and millet-cowpea rotations than the continuous
pearl millet cropping supplied with 45 kg N ha−^1 (Mukurumbira 1985 ). In Malawi,
MacColl ( 1989 ) reported that the maize grain yield with no fertilizer application
after pigeonpea was 2.8 t ha−^1 more than a maize-maize rotation supplied with 35 kg
N ha−^1 on annual basis.
In a long term experiment on vertisol, Rego and Rao ( 2000 ) found that the con-
centration of N in the surface (0–15 cm) layer was enhanced by 125 mg N kg−^1 of
soil in a pigeonpea –based cropping system with not no external N input after 12
years. On the other hand, there was rapid decline in total N concentration in the
traditional (rainy season fallow, post rainy season sorghum) and in non-legume
based cropping systems. These improved management practices not only lessen soil
loss through erosion, but also enhanced the accumulation of total N and carbon with
substantial improvement in crop yield (Wani et al. 2003 ).
Pasture and forage legumes in a cereal-sheep ley farming system in Australia
(Puckridge and French 1983 ) provide not only fodder for livestock, but also the
mineralized N for the subsequent cereal crop (Hossain et al. 1996 ). Likewise, sev-
eral other studies in USA has reported that the rotation of legumes with cereals
improves the soil N and thus provides diversification of crops (Norwood 2000 ;
Carpenter-Boggs et al. 2000 ). Few other crop rotations showed positive impacts of
these rotations not only on the soil properties (especially soil organic matter), but
also on water use efficiency and nutrient use (Pala et al. 2007 ; Ryan et al. 2008a, c).
3.4.2 Organic Manures and Crop Residues
Chemical fertilizers should be applied at optimal dose together with use of crop
residues and organic manures. Indeed, most of the dryland soils are low in soil
organic matter due to high temperature or low recovery of plant residues which are
used by the animals, as fuel or as thatching material and are not returned to the soil.
Any improvement in soil organic matter will improve soil physical properties as
well as nutrient status of the soil (FAO 1988 ). Organic matter may be applied as
bulky organic manures (crop residues, compost, farmyard manure) or municipal
sludge or may be grown in situ as green manure crop and incorporated into the soil.
Usually, the coarse textures dryland Alfisols has low organic matter and are sub-
jected to crust formation which impacts the seedlings establishment and further
plant growth. In this situation, the incorporation of crop residues after the harvest of
grain crops may improve the fertilizer use efficiency and crop productivity (Hegde
1980 ). Soil organic matter contents were also enhanced from 0.55 to 0.90 %, and the
yields of cowpea and pearl millet were enhanced by 14 and 19 %, respectively after
5 years of crop residue application. Restoration of crop residues in the soil enhanced
A. Nawaz and M. Farooq