Characterization Of Rotor-tiller Straw Incorporation And Management Effects On Soil Quality And Productivity In A Rice-wheat Rotating System

Reduced-till-straw-incorporation in the context of sustainable agriculture has always been the center of attention to many farmers,soil scientists and policy makers in Rice-Wheat(R-W)rotation in China.While there are benefits to leave straw on the ground surface,including increased resistance to wind and water erosion,there are also drawbacks.Excessive straw on soil surface makes it more difficult to plant and cultivate,and the residue layer also cools down the soil,which can slow emergence of the next crop.Thus,the amount of straw required for surface cover will be based on the desired soil attributes in relation to surface crop residue pattern.Therefore,it is paramount to determine a proper straw measurement method for better understanding the amount of straw left and its distribution on the soil surface.The rice and wheat growing farmers have traditionally used numerous tillage operations to break up and bury crop straw.Their goal is a seedbed with loose soil and little or no residue cover.Such tillage systems incorporate crop straw,providing warmer soils and making planting easier,but it also has several drawbacks.The loose soil left after tillage is easily compacted by heavy equipment.And the bare and pulverized soil is vulnerable to wind and water erosion.Because of these problems and for economic concerns,farmers in this region have begun to implement conservative tillage systems.Rotor-tiller is a representative one of such systems.Keeping in view all these facts,this research work was carried out to develop an accurate and easy-to-handle field method to quantify the proportion of ground cover;and to investigate the performance of the rotor tillage straw incorporation(RTSI).Furthermore,the effect of incorporated straw on soil physical properties was studied.The results are generalized as following:1.To quantify the straw mass distribution on soil surface,the mass-based image analysis method for evaluating straw cover was applied.Mass and cover relationships were investigated and analyzed to evaluate straw distribution on the soil surface,by comparing surface cover from three different combine harvesters in a rice-wheat(R-W)cropping system.For each harvester,straw distribution on the ground was measured and virtually reconstructed,and then the straw stacked layers analyzed.The mean straw mass distribution and percent surface cover measured in 2014 and 2015 ranged between 4.2-12 t ha-1 for all the harvesters.Flat straw mass was higher than standing stubble mass in all treatments.The most important observation is that the distribution pattern of straw depended on instantaneous material feed rate through the harvester;the higher the feed rate,the poorer the straw distribution uniformity.The Xinjiang Ceres 4LZ-2.5 harvester outperformed all the other harvesters.These findings can improve the estimation of straw cover for tillage straw incorporation or no-till straw return fields and indicates that straw condition should be considered in mass-to cover relationships.2.T o investigate the performance of the RTSI,a field experiment was carried out in a rice-wheat rotating area in east of China with controlled blade shape(i.e.bent C5 flat C and hoe type),rotating speed(i.e.200,280,360 and 440 rpm)and straw length(i.e.5,15 and 25 cm).The managed soil was sampled and the incorporated straw was digitized with a 3D digitizer.Acquired data was then modeled in Pro/E to quantify the straw distribution within soil profile,been parameterized with straw length,color and straw orientation.Results showed that incorporation of straw was significantly improved with increased rotating speed,regardless of the straw length and tillage tool types.The bent C-type blade resulted in 10%and 30.9%more straw incorporation as compared with flat C-type and hoe-type blade,respectively.Soil fragmentation was significantly increased with rotating speed.The rotor-tiller with bent C-type blades had the lowest torque variation and specific work requirement compared to other two types.Therefore the bent C-type and flat C-type blades at the speed of 280 and 360 rpm would be the preferred options for RTSI.Considering the intensified cropping system within the constraints of a number of featured boundary conditions(e.g.,overabundance of straw cover,compact crop rotation tightened by limited annual heat and radiation,humid climate and fragile soil tilth under intensified field trafficking),the RTSI provided an optimized management of soil and crop residue for immediate shifting of crops,and reduced soil disturbance with one-pass field operation.Therefore the RTSI is defined as an intensified conservative tillage system.Additionally,3D modeling of managed soil and crop straw could be a tool for improved design of conservative tillage systems.3.To investigate the straw incorporation with forward and backward of rotor-tilling,field experiment was conducted using an in-situ test rig with rotor-tiller.Three straw mixtures(G1,G2 and G3)were used at three speeds(200,360 and 400 rpm)in paddy soil.Straw distribution in soil was measured with a 3D digitizer and then virtually reconstructed in Pro/E.Results showed that the 3D method was an effective way of illustrating straw distribution in soil profile.The straw incorporation significantly increased with forward as compared with backward rotation.In the forward rotation,there were 50.4%,32%and 17.6%straw incorporated into the soil layers of 0-5,5-10 and 10-15 cm,respectively.The backward,a total of 68.4%,22%and 9.5%straw were incorporated into the soil layer of 0-5,5-10 and 10-15 cm,respectively.Additionally,greater MWD were achieved with forward and higher speed compared to backward rotor-tiller and lower speed.We concluded that the forward rotation of 360 and 400 rpm were the best options for incorporating straw and improving soil quality for R?W cropping system in China.4.To investigate the effects of straw incorporation on short-term responses of soil Cone Index(Cl),Bulk Density(BD)and Biopore(BP),we conducted a 2-yr(2015-2016)experiment in the lowland of Yangtze River Delta.Five treatments were tested:(?)no straw incorporation(0S);(?)25%straw incorporation(25S);(?)50%straw incorporation(50S);(?)75%straw incorporation(75S);(?)100%surface mulch(100M).The Cl and BD were determined at depths of 10,20 and 30 cm while BP was determined in 0-20 cm depth.Root distribution index(RDI)was measured with a 3D digitizer then virtually reconstructed in Pro/E.It was observed that Cl and total BD decreased by 16.2%and 7.4%,respectively.Soil porosity within 0-30 cm soil depth was proportionally increased with increasing straw application as compared with 0S.In addition,deeper root penetration coupled with greater pores was achieved with straw incorporation as compared with 0S and 100M.We concluded that the 75%straw incorporation rate might be a good option for improving soil physical properties in the R-W cropping system in China.