Long-term effects of organics, fertilizers and cropping systems on soil physical productivity evaluated using a single value index (NLWR)

Effect of different cropping systems, viz. maize-wheat (M-W), rice-wheat (R-W), soybean-wheat (S-W), and perennial grasses (guinea grass and setaria grass), in vogue since 6-32 years, and long-term use of chemical fertilizers (N, NP, NPK and NPK + lime) and organic materials (FYM, wheat straw, lantana biomass) on physical productivity of medium-textured (silt loam and silty clay loams) soils was investigated using non-limiting water range (NLWR) as the soil physical index. Higher the NLWR better is the soil physical condition for crop growth. The sources of N, P and K were urea, single superphosphate and muriate of potash, respectively. The NLWR was highest in S-W (16.8%), followed by grasses (14.4-15.6%) and M-W (13.1-15.4%), and lowest in R-W (7.5-11.0%). Under M-W system (32 years), NLWR was highest in NPK (13.1%), followed by NP (12.2%), NPK + lime (9.4%) and control (9.0%), and lowest in N (7.7%). Application of organics increased the NLWR in both M-W and R-W (6-18 years) systems; the NLWR values with and without organics were 18.0 and 17.1% in M-W, and 14.1-15.9 and 15.7-17.2% in R-W system. The NLWR was linearly, significantly and positively correlated with wheat grain yield (r = 0.646**, -0.706**). The NLWR:PAWC (plant available water capacity) ratio (higher the ratio, better is the soil physical condition), which was 0.58 in control, decreased with N (0.49) but increased with NP (0.72) and NPK application (0.77); use of organics further improved the ratio. The NLWR:PAWC ratio was highest in S-W (0.97), followed by grasses (0.88-0.91), M-W (0.77-0.86) and R-W (0.54-0.68) system. Thus, long-term use of urea alone deteriorated, while NPK at recommended rates improved soil physical productivity over the control of no fertilizer application; the effect further improved when NPK were combined with organic sources. Among different cropping systems, the soil physical productivity followed the order: S-W > grasses > M-W > R-W system. (c) 2007 Published by Elsevier B.V.