Characterization and modeling of soil physical environment in rice-wheat and cotton-wheat systems under conservation agricultural practices.

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Date
2013
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IARI, DIVISION OF AGRICULTURAL PHYSICS
Abstract
In the present study an attempt has been made to characterize the soil physical environment under different conservation agricultural practices in rice-wheat and cotton-wheat systems. In the cotton-wheat system, the treatments were : conventional tillage (CT), zero tillage (ZT), permanent narrow beds (PNB), permanent broad beds (PBB), ZT with residue (ZT+RES), PNB with residue (PNB+RES) and PBB with residue (PBB+RES). In the rice-wheat system , the treatments were : Direct-seeded rice– zero till wheat (DSR- ZTW), DSR + Sesbania brown manuring – ZTW (DSR+BM-ZTW) and puddled transplanted rice – conventional tilled wheat ( TPR-CTW). For computation of least limiting water range (LLWR), the required soil resistance curve was drawn by measuring penetration resistance (PR) in field using an automatic Rimik cone penetrometer instead of commonly used laboratory method of measuring PR in undisturbed soil cores by manual penetrometer. Results revealed that the plots under TPR-CTW had higher PR (>2MPa) in the 15-30 cm soil layer. This clearly indicated that intense puddling for rice cultivation and several passes of cultivator and disc harrow for wheat seed bed preparation in previous three years increased subsurface compaction. On the other hand, under DSR+BM-ZTW, the magnitude of PR of the 0-60 cm profile was less than 1.4 MPa, indicating less compaction and relatively favorable soil physical environment due to zero tillage in wheat along with brown manuring before rice transplanting. In the cotton-wheat, PR (kPa) of 0-45cm soil layer was in the following order: PBB+RES <PNB+RES <PBB <PNB <ZT+RES <CT <ZT. Due to residue retention during four crop seasons (two crop cycles) in the ZT+RES, PNB+RES, and PBB+RES treated plots, soil bulk density and PR of the surface soil layer were reduced compared to the treatments without residue. 39 39 Results further showed that both in rice-wheat and cotton-wheat systems, for all CA treatments aeration became aplant-growth limiting factor beyond bulk density (BD) values of 1.55 to 1.6 Mg m-3 and penetration resistance became limiting factor beyond BD values 1.65 Mg m-3. With increase in BD, the magnitude of LLWR rapidly declined in the sub-surface layer (15 – 30 cm) compared to surface layer (0-15 cm). More decline in LLWR in the sub-surface layer in conventional tillage practices compared with CA practices in both rice-wheat and cotton –wheat systems is an indicator of increased compaction, poor soil structural condition and limited water availability in the sub-surface layer. In the rice –wheat system, LLWR values of both surface and sub-surface layers werehigher in DSR +BM – ZTW than conventional practice (TPR-CTW). These results thus confirmed earlier findings that brown manuring under no tillage improved soil structural condition. In the 0-15 cm soil layer, the plots under PBB+RES had nearly 16, 16 and 51% higher LLWR than CT (12.1%), PNB+RES (12%) and ZT (9.3%) plots. The impact of PBB+RES on improvement in LLWR over CT plots in the sub-surface layer was much higher than the surface layer. In the 15-30 cm soil layer, PBB+RES treated plots had ~79% higher LLWR compared with CT plots (LLWR = 6.1%). This result is of tremendous importance to sustainable productivity of the cotton-wheat system under CA and probably very novel in the South Asia. Residue addition invariably improved LLWR values in both soil layers for all treatments. For instance, in the 0-15 cm soil layer, plots under ZT+RES, PBB+RES and PNB+RES had nearly 23, 25 and 11% higher LLWR than ZT, PBB and PNB plots. There was a drastic reduction in LLWR in the ZT plots in the sub-surface layer and CT plots had much better LLWR than ZT plots in that layer. This indicates that ZT without residue addition had deleterious impact on soil water availability and structural property and should be avoided. Key words: bed planting, zero tillage, least limiting water range ,soil penetration,
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T-8810
Keywords
bed planting, zero tillage, least limiting water range ,soil penetration, conservation agriculture
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