Physical characterization of a soil amended with organic residues in a rice-wheat cropping system using a single value soil physical index

The effect or soil incorporations of lantana (Lantana spp.) biomass, an obnoxious weed, on physical environment of a silty clay loam soil (Typic Hapludalf) under rice (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping was studied in a longterm field experiment conducted in a wet temperate region of north India. Fresh lantana biomass was incorporated into the plough layer at 10, 20 and 30 Mg ha(-1) annually, 7-10 days before puddling. Plant-available water capacity (PAWC), nonlimiting water range (NLWR) and NLWR:PAWC ratio were determined to characterize soil physical environment during wheat crop in the tenth cropping cycle. Ten annual applications of lantana at 10, 20 and 30 Mg ha(-1), increased organic carbon (OC) content over control by 12.6, 17.6 and 27.9%, in 0-15 cm soil layer, and 17.1, 26.3 and 39.5% in 15-30 cm soil layer, respectively. The OC content in 0-15 and 15-30 cm soil layer of control plots was 11.1 and 7.6 g kg(-1) soil. Bulk density decreased by 3-14% in 7.5-10.5 cm layer and 1-6% in 15-18 cm layer. Volumetric moisture contents at 10% air-filled porosity were 38.3, 40.0, 54.5 and 55.7% at 7.5-10.5 cm depth. and 31.4, 32.2, 33.9 and 34.6% at 15-18 cm depth corresponding to 0, 10, 20 and 30 Mg ha(-1) lantana treatment, respectively. At 15-18 cm soil depth, volumetric moisture contents rat 2 MPa soil penetration resistance wet e 26.9, 24.8, 23.0 and 19.6% in zero, 10, 20 and 30 Mg ha(-1) lantana-treated plots, respectively. Lower soil water contents associated with 10% air-filled porosity and greater soil water contents associated with a limiting penetration resistance of 2 MPa resulted in a lower NLWR (4.3%) for control as compared to lantana-treated soil (7.4-15.1%). The PAWC showed slight increase from 12.9 to 13.4-14.9% due to lantana additions. The NLWR:PAWC ratio was also lower in control (0.33) as compared to lantana-treated soil (0.55-1.01). The NLWR was significantly and positively correlated with wheat grain yield (r = 0.858**). (C) 2001 Elsevier Science B.V. All rights reserved.