Weed Dynamics, Soil Health and System Productivity in Conservation Rice-wheat Cropping Systems

Abstract

Rice (Oryza sativa L.) and wheat (Triticum aestivum L.) are consumed as staple food by billions across the globe. Both crops are grown in multiple cropping systems but rice-wheat cropping system (RWCS) is the most prominent one in south Asia including Pakistan. However, the productivity of this system is threatened due to increasing labor, water and energy crises in the region, and the negative impact of soil management interventions on soil and aerial environments. In this scenario, conservation RWCSs offers an ecofriendly option to reduce water, labour, and energy input, and improve soil health. We conducted a series of experiments. In experiment I, conducted at Agronomic Research Area, University of Agriculture, Faisalabad, the impact of sesbania brown manuring (SBM) in direct seeded aerobic rice (DSAR), and rice residue mulch (RM) in zero tilled wheat (ZTW) on weed dynamics, soil health and system productivity was evaluated. The experiment was comprised of five RWCSs viz. (i) DSAR-ZTW, (ii) DSAR+SBM-ZTW, (iii) DSAR-ZTW+ RM, (iv) puddled transplanted flooded rice (PudTR)-ZTW, and (v) PudTR- plough tilled wheat (PTW). The SBM in DSAR reduced the density and dry weight of weeds by 41-56 and 62-75%, respectively than sole crop of DSAR. At rice harvest, minimum soil bulk density, highest total nitrogen (N), soil organic carbon (SOC) and soil microbial biomass carbon (SMBC) were recorded with DSAR+SBM-ZTW, which eventually improved the grain yield, water productivity and profitability of DSAR in this RWCS. Rice residue mulch retention in ZTW reduced the density and dry biomass of weeds by 60 and 69%, respectively than ZTW with no residue mulch. At wheat harvest, highest total N, SOC, and SMBC were recorded with DSAR-ZTW+RM, followed by DSAR+SBM-ZTW, which eventually led toward better wheat grain yield and profitability and improved system productivity in these RWCSs. In experiment II, conducted at same site, potential role of seed priming in improving the stand establishment, grain yield, water productivity and profitability of wheat grown in various RWCSs was evaluated. For seed priming, wheat seeds were soaked in aerated water (hydropriming) or solution of calcium chloride (ψs -1.25 MPa; osmopriming) for 12 h; non-primed seeds were used as control. After harvest of DSAR and PudTR crop, primed and non-primed wheat seeds were sown following zero tillage (ZT) and plough tillage (PT). In both years, stand establishment of ZTW after DSAR and PudTR was impeded; nonetheless, seed priming improved the stand establishment which was visible through earliness and better uniformity of seedling emergence. Improved stand establishment enhanced growth, grain yield, water productivity and profitability of wheat in ZT systems. In this regard, osmopriming was the most effective. The third experiment was conducted for 2-years at two experimental sites (Nankana Sahib, Sheikhupura). During both years, rice was grown both as DSAR and PudTR; followed by PTW and ZTW after each rice production system at both sites. Overall, higher total N, SOC, SMBC, and SMBN were recorded in DSAR than PudTR, and DSAR yielded similar as the PudTR. However, net benefits and water productivity was the highest with DSAR than PudTR. In wheat season, the highest total N, SOC, SMBC, and SMBN were recorded for DSAR-ZTW, which eventually enhanced the grain yield, water productivity and profitability in this RWCS. In experiment IV, the impact of no tillage (NT) and PT, with or without wheat residue mulch on soil properties and greenhouse gases emission was evaluated. This experiment was started 27 year ago on a Crosby silt loam soil at Waterman Farm, The Ohio State University, Columbus, Ohio, USA. Mulching reduced soil bulk density and improved total soil porosity. More total carbon, SOC and SMBC were recorded in soil under NT than PT. Mulching increased total C, SOC and SMBC by 18, 72 and 8%, respectively than un-mulched control. Seasonal fluxes of greenhouse gases were lowest under NT than PT; however, mulching enhanced nitrous oxide emission. In experiment V, we interviewed the farmers from four districts (Nankana Sahib, Sheikhupura, Faisalabad, and Sialkot) to know their perceptions, and problems about the conventional and conservation RWCS. Majority of the farmers were facing the problems of water and labor shortage. Most of the farmers were afraid of adopting the DSAR due to fear of weeds, while many of them were not adopting DSAR due to lack of know how about this technology. Majority of the farmers reported that they have no access to ZTW drill due to which they are not adopting it. In crux, weed management in DSAR through SBM followed by wheat planting with ZT using primed seeds may be opted to improve the productivity, profitability, soil health, and to reduce the greenhouse gases emission from RWCS. Provision of conservation machinery for rice and wheat planation at affordable rates, aided by on farm demonstration of weed management practices developed for DSAR and ZTW, through participatory research may help to improve the uptake of DSAR and ZTW. Long term NT reduced the greenhouse gases emission by improving soil properties. However, mulching increased the greenhouse gases emission.