| Tillage is the mechanical manipulation of soil to provide suitable environment for germination,growth and yield of crops.The incorporation of the crop straw into the agricultural soil is crucial factor.It directly affects organic carbon dynamics,soil fertility,water and wind erosion,sediment delivery,growth and yield of crops.In contrast,the proper information on the appropriate amount/percentage of straw incorporation is not available.It is generally believed that at least 30%of the soil surface should be covered with straw.Nevertheless,the application of straw on the 30%of the soil surface is not yet clearly understood.Although,many remote sensing and GIS based studies have been conducted to estimate the straw cover percent and spatial distribution for crop area mapping of agricultural fields.There are no methods currently available,which quantify and monitor the wheat straw cover(WSC)percent and their effect on crop yield in a rice-wheat cropping system at large scale on a continuous basis.Therefore,keeping above facts in view,a series of field experiments were conducted at Jiangpu agricultural farm Nanjing,China during 2015-2017 to investigate the effect of tillage and straw incorporation on soil physicochemical properties,soil organic carbon(SOC),soil carbon storage(SCS)and grain yield in a rice-wheat rotational system with eight treatments.The treatments included ⅰ)reduce tillage+30%straw incorporation(RTsi30),(ⅱ)reduced tillage+60%straw incorporation(RTsi60),(ⅲ)reduced tillage+100%(RTsi100),(ⅳ)reduced tillage+no straw(RTns),(ⅴ)conventional tillage+30%straw incorporation(CTsi30),(ⅵ)conventional tillage+60%(CTsi60),(ⅶ)conventional tillage+100%(CTsi100 and ⅷ)conventional tillage+no straw(CTns).The wheat straw cover percent,and the performance of rice crop estimated through remote sensing and GIS based techniques with combination of Landsat satellite data and seven RS based indices,including ⅰ)normalized difference vegetation index(NDVI)ⅱ)normalized difference tillage index(NDTI),ⅲ)Simple tillage index(STI),ⅳ)normalized difference index 7(NDI7),v)normalized difference index 5(NDI5),vi)normalized difference senescent vegetative index(NDSVI)and vii)Shortwave red normalized difference index(SRNDI)to develop models for the estimation of WSC and yield of rice crop under different percentages of straw cover over the study area in Changshu City,China in a rice-wheat cropping system for long-term agricultural sustainability.The main study results are summarized as follows:1.The application of rice straw incorporation showed a positive impact on soil fertility,physical characteristics and crop yield after two cropping cycles of wheat crop.The results of current study reavels that 60%of straw incorporation under reduced tillage method(RTsi60)treatment was positively achieved higher crop yield and enhanced soil quality as compared to other treatments.However,soil dry bulk density(0-30 cm)reduced significantly(1.16%to 7.73%)under all treatments as compared to the pre-treatment,while the highest soil ρb reduction was found under 100%straw incorporation with conventional tillage method(CTsi100)treatment as 1.22 g/cm3 and lowest was determined(1.30g/cm3)under no straw with reduced tillage(RTns).The average soil porosity increased by 7.09%to 1.15%as compared to before experiment values,whereas the highest porosity was observed 54.14%under conventional tillage with 60%straw incorporation(CTsi60)at depth of 0-10cm soil profile.2.The maximum soil organic carbon(SOC)content was found 15.34 g/kg under RTsi60,while the considerable variation of SOC was noted at the depth of 0-10 cm.The SOC was significantly(P<0.05)higher under RTsi60(16.26 g/kg)followed by RTsi100(15.45 g/kg)at the end of field of experiment under different rice straw incorporation.Consequently,maximum soil carbon storage(SCS)was determined 7373.40 kg/ha under RTsi60 treatment as compared to no straw incorporation treatment plot.In the regard of crop yield performance under rice straw incorporation,the highest crop yield was recorded under CTsi60(4156.98 kg/ha)and lowest was found 3201.50kg/ha under no-straw with reduced tillage(RTns)treatment.3.The study results explored that wheat straw incorporation and reduced tillage methods had significant effects on crop yield and soil quality indices in 0-30 cm soil layer when compared with treatments having no straw incorporated.While,the maximum reduction of 9.79%in soil dry bulk density(pb)was found under reduced tillage with 100 percent of rice straw incorporation treatment plot(RTsi100),and minimum(1.31%)occurred under no straw with conventional tillage practice(CTns).4.The soil fertility analysis revealed that wheat straw incorporation increased the concentration of total nitrogen(TN),available phosphorus(AP)and available potassium(AK)in the soil profile(0-30 cm).Maximum TN was found under RTsi60(0.981 g/kg)followed by RTsi100(0.969 g/kg).Whereas,the highest AP and AK were determined 37.65mg/kg and 82.23 mg/kg respectively,in RTsi60 treatment and lowest was observed under conventional tillage practice with no-straw incorporation treatment plot.Moreover,the wheat straw incorporation also significantly increased the soil organic matter(SOM)level by 3.08-17.07%compared to the treatments without straw incorporation.While,the maximum average SOM and SCS were achieved 25.12g/kg and 6971.54 kg/ha respectively,under 60 percent of straw incorporation with reduced tillage(RTsi60)treatment.5.The incorporated wheat straw into soil,significantly(p<0.05)achieved the highest rice grain production and crop growth parameters as compared to without straw incorporation during two rice growing cycle.While,the highest mean grain yield(8.29 ton/ha),spike number(309.72 × 104/hm2),and grains per spike(132.24)were found under RTsi60.Whereas,thousand grain weight(TGW)was marginally higher under reduced tillage with 30 percent amount of straw incorporation(RTsi30)treatment.These results further reveal that 60%wheat straw incorporation into the soil for either tillage practice had a progressively positive impact on the rice crop grain yield compared to 100%straw or without straw incorporation.6.An novel model was established through Remote Sensing(RS)and GIS techniques to accurately estimate the wheat straw cover percent and the crop yield under distinct percent of straw incorporation by using the satellite ancillary data at large scale.Moreover,the normalized difference tillage index(NDTI)was found to be the best to estimate and mapping wheat straw cover percentage in different categories(i.e.>40%,41-60%,61-80%and 81-100%)with R2=0.80 and overall accuracy 84.61%(κ=0.76)as compared to other crop residue indices.7.The yield prediction model for rice crop was successfully developed by correlating NDVI index values through sampling points and rice production obtained through ground recorded data with an R-squared(R2=0.85).Whereas,the highest estimated rice yield(8439.67 kg/ha)was recorded under 68%of WCS and the maximum yield density(0.082)was calculated in the range of 65-78%straw cover percentage with an average yield from 8300 to 8400 kg/ha through bivariate kernel density estimates at the sampling points of the study region.In the summary,the incorporation of 60%-70%of crop straw under reduced tillage method improved soil quality,decreased soil dry bulk density,increased soil porosity,organic carbon and storage dynamics,which in turn increased the crop growth and yields.Hence,straw incorporation found to be efficient to improve soil quality,increase soil organic carbon stocks and enhance yield of crops in a rice-wheat cropping system for agricultural sustainability.Additionally,current study confirmed that the NDVI,STI and NDTI algorithm are very effective and robustness indicators to measure the straw cover percent and successively determine the impact of different WSC percentages on crop yield under rice-wheat rotational system within single field or across large regions through RS and GIS techniques.It is useful for long-term land use,which based on the development of agricultural sustainable. |
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