EFFECT OF GREEN MANURING ON THE PHYSICAL-PROPERTIES OF SOIL UNDER A RICE WHEAT CROPPING SYSTEM

The effects of green manuring with Sesbania aculeata, or with Leucaena leucocephala leaves and of weed incorporation on the physical propert ies of a clay loam soil under a rice-wheat rotation were compared at N ew Delhi, India, in 1986-87. Under puddled conditions, the volumetric moisture content of the saturated topsoils varied from 0.400 cm3/cm3 i n the Sesbania-treated plots to 0.425 cm3/cm3 in plots receiving no gr een manure, but in the unsaturated soils at rice harvest the correspon ding values were 0.317 and 0.271 cm3/cm3. The effects of the green man ures on the water content of the soils were still evident after a subs equent wheat crop. Other soil physical properties affected by the trea tments were the following (data refer to topsoils measured after the r ice harvest): settling index (cm/cm), an estimate of structural instab ility, which ranged from 25.5% (Sesbania-treated plots), to 28.6% (wee d incorporation), 29.7% (Leucaena-treated plots) and to 33.5% (NPK-fer tilizer only). Soil dispersion increased from 6.0 to 10.0 g/100 g thro ugh the same treatment sequence. Hydraulic conductivity in the NPK-fer tilizer only plots was 3.1 cm/day, but increased to 4.8 cm/day in the Sesbania-treated plots. Sesbania was superior to the other green manur es for improving soil physical properties after its incorporation.