SOIL STRUCTURAL IMPROVEMENTS WITH THE ADDITION OF LANTANA-CAMARA BIOMASS IN RICE-WHEAT CROPPING

A long-term field experiment was initiated in June 1988 in a silty cla y loam soil to investigate the potential of Lantana camara, an obnoxio us weed, for improving structural properties and productivity of soil in rice-wheat cropping. Lantana was incorporated into the soil 10-15 d ays before puddling at 10, 20 and 30 t/ha (fresh weight). At the end o f the sixth cropping season, Lantana additions increased the organic c arbon (OC) of the 0-15 cm soil layer by 11-24%, and of water-stable ag gregates (WSA, 0.50-8.0 mm diameter) by 10-21%; OC of WSA < 0.50 mm di ameter remained unaffected. About 17-25% of the applied OC was retaine d in the soil. The OC increase resulted in a decrease in bulk density of the plough layer (0-15 cm) by 7%, a decrease in aggregates of 2-8 m m diameter and of clods by 4% and 6%, respectively. There was an incre ase in water-stable aggregates and aggregate porosity, and a decrease in clod-breaking strength from 420 to 216 kPa. Soil cracking at the su rface changed from wide, deep cracks in hexagonal pattern to a close-s paced network of fine cracks. Lantana additions increased < 5 mm wide cracks at the expense of 10-20 mm wide cracks; 5-10 mm wide cracks rem ained unchanged. Total volume of cracks decreased by 36% and surface a rea of cracks by 55% compared with the control plots.