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Soil biochemical changes at different wheat growth stages in response to conservation agriculture practices in rice-wheat system of north-western India
Intensive tillage, removal or burning of crop residues, limited organic manure use, declining irrigation water resources and scarcity of labor are the major causes of soil degradation and unsustainablilty of rice (Oryza sativa L.) - wheat (Triticum aestivum L.) system (RWS) in South Asia . Resource conservation technologies (RCTs) such as zero tillage (ZT), dry direct seeded rice (DSR) and crop residues retained as mulch have shown promise to increase the productivity and profitability of RWS in South Asia. Effects of RCTs on soil biological parameters are less clear and contradictory. We evaluated the effects of conservation agriculture practices on changes in soil biochemical properties at different growth stages of wheat grown as fifth crop in RWS. Twelve treatment combinations of tillage, crop establishment and crop residue management included four main plot treatments in rice (1) conventional till (CT)-DSR, (2) ZT-DSR, (3) DTR, ZT machine transplanted rice and (4) PTR, conventional puddled transplanted rice) and the three sub-plot treatments (i) CTW-R , CT wheat with both rice and wheat residues removed, (ii) ZTW-R, ZT wheat with residues of both the crops removed and (iii) ZTW+R , ZT wheat with rice residue retained as surface mulch in subsequent wheat. Irrespective of rice establishment methods, increase in mean wheat grain yield under ZTW+R was 6% and 10% compared with CTW-R and ZTW-R, respectively. Soil enzyme activities (5 to18%) increased under ZTW+R compared with ZTW-R and CTW-R at all growth stages of wheat. Residual effect of rice straw establishment methods was significant on soil enzyme activities during wheat cropping, which were highest under ZT-DSR followed by CT-DSR, DTR and PTR. Soil organic carbon content in 0-7.5 cm layer was significantly higher by 7 to 9 % under the ZTW+R treatment compared with all the other treatments. Principal component analysis (PCA) identified three enzyme activities (dehydrogenase, fluorescein diacetate and phosphatase), and soil organic carbon content as the most sensitive indicators for assessing soil quality for conservation agriculture based RWS. PCA discriminated rice establishment systems with rice residue as surface mulch (+R) from rice establishment systems without rice residue (-R) and the maximum tillering stage from the other stages of wheat. The present study provided reliable biochemical indicators to monitor soil biological quality changes in response to conservation agriculture practices in RWS.
SR16357 Accepted 17 July 2017
© CSIRO 2017