Impact of conservation tillage in rice–based cropping systems on soil aggregation, carbon pools and nutrients

Rajiv Nandan,Vikram Singh,Sati Shankar Singh,Virender Kumar,Kali Krishna Hazra,Chaitanya Prasad Nath,Shishpal Poonia,Ram Kanwar Malik,Ranjan Bhattacharyya,Andrew Mcdonald

doi:10.1016/j.geoderma.2019.01.001

Abstract

Tillage intensive cropping practices have deteriorated soil physical quality and decreased soil organic carbon (SOC) levels in rice–growing areas of South Asia. Consequently, crop productivity has declined over the years demonstrating the need for sustainable alternatives. Given that, a field experiment was conducted for six years to assess the impact of four tillage based crop establishment treatments [puddled transplant rice followed by conventional tillage in wheat/maize (CTTPR–CT), non–puddled transplant rice followed by zero–tillage in wheat/maize (NPTPR–ZT), zero–till transplant rice followed by zero–tillage in wheat/maize (ZTTPR–ZT), zero–tillage direct seeded rice followed by zero–tillage in wheat/maize (ZTDSR–ZT)], two residue management treatments [residue removal, residue retention (~33%)], and two cropping systems [rice–wheat, rice–maize] on soil aggregation, carbon pools, nutrient availability, and crop productivity. After six years of rotation, in top 0.2 m soil depth, zero–till crop establishment treatments (ZTTPR–ZT and ZTDSR–ZT) had higher (p < 0.05) total organic carbon (TOC) over conventional tillage treatment (CTTPR–CT). Zero–till crop establishment treatments increased very–labile C faction (Cfrac1) by 21% followed by labile fraction (Cfrac2) (16%), non–labile fraction (Cfrac4) (13%) and less–labile fraction (Cfrac3) (7%). Notably, higher passive C–pool in conservation tillage practices over CTTPR–CT suggests that conservation tillage could stabilize the recalcitrant form of carbon that persists longer in the soil. Meantime, zero–till crop establishment treatments had higher (p < 0.05) water stable macro–aggregates, macro–aggregates: micro–aggregates ratio and aggregate carbon content over CTTPR–CT. The treatment NPTPR–ZT significantly increased soil quality parameters over CTTPR–CT. However, the effect was not as prominent as that of ZTTPR–ZT and ZTDSR–ZT. Retention of crop residue increased (p < 0.05) TOC (12%) and soil available nutrients mainly available–P (16%), followed by available–K (12%), DTPA–extractable Zn (11%), and available–S (6%) over residue removal treatment. The constructive changes in soil properties following conservation tillage and crop residue retention led to increased crop productivity over conventional CTTPR–CT. Therefore, conservation tillage (particularly ZTTPR–ZT and ZTDSR–ZT) and crop residue retention could be recommended in tropical rice–based cropping systems for improving soil quality and production sustainability.

Highlights

The adverse impact of intensive tillage practices on soil physical quality and soil organic carbon (SOC) levels is a major challenge in tropical rice–growing regions (Chauhan et al, 2012; Srinivasan et al., 2012)
Conservation tillage treatments (NPTPR–ZT, ZTTPR–ZT and ZT direct seeding of rice (ZTDSR)–ZT) had 13–21%, 12–16%, 5–7%, 9–13%, and 9–14% higher (p < 0.05) Cfrac1, Cfrac2, Cfrac3, Cfrac4, and total organic carbon (TOC), respectively, over conventional puddled transplanting rice (CTTPR)–CT
It is concluded that zero–till crop establishment practices (ZTTPR–ZT and ZTDSR–ZT) in rice–based systems had a positive impact on soil organic C–pools, macro–aggregate formation, and carbon stock in aggregates

Summary

Introduction

The adverse impact of intensive tillage practices on soil physical quality and soil organic carbon (SOC) levels is a major challenge in tropical rice–growing regions (Chauhan et al, 2012; Srinivasan et al., 2012). Added to this, limited or no use of organic manures/crop residue (Ghosh et al, 2016), lack of crop diversification (Hazra et al, 2014), imbalanced use of mineral fertilizers (Brar et al, 2013) have further aggravated soil quality deterioration. Conventional puddled transplanted rice management systems require more water and create ecologies that favour emission of methane – a potent greenhouse gas (Hou et al, 2000; Hazra and Chandra, 2016). Alternative soil and crop management practices are needed to alleviate the adverse consequences of conventional puddled rice–based production systems and to remain sustainable in long–run

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