Effects Of Straw Return On Soil Fertility And Potassium Fertilizer Reduction In Maize-rice Cropping System

The maize?Zea mays L.?-late rice?Oryza sativa L.?rotation system has developed in the middle reaches of Yangtze River in China in recent years.Farmer often directly abandon or burn the straw for convenience,which not only caused serious pollution to the environment,but also wasted available resources.Straw contains rich nutrients such as nitrogen,phosphorus and potassium,and will increase soil fertility after return to the field.Most of the potassium fertilizer in China depends on imports.Meanwhile,the potassium contained in the straw is in the form of ions,when straw return to the field,the potassium in the straw will supplement the potassium of the soil.Therefore,exploring effects of straw on the increment of soil fertility and substitution of potash is meaningful.This field experiment was conducted in Qujialing downtown,Jingmen City,Hubei province,during 2016-2018.The maize-rice system,which is a developing cropping system in the middle reaches of the Yangtze River in China,was selected in this study.We set up four treatments,including?1?no straw return?CK?;?2?only rice straw incorporated to field?M₀Rs?;?3?both maize and rice straws incorporated to field?Msr-Rs?;and?4?maize straw mulched and rice straw incorporated to field?Msc-Rs?,meanwhile concluded four different potash fertilizer reduced treatments:S0K0?no maize and rice straw return,no K fertilizer usage?,Sr K0?both maize and rice straw return,no K fertilizer usage?,Sr K33?both maize and rice straw return,33%K fertilizer usage?and Sr K67?both maize and rice straw return,67%K fertilizer usage?.The effects of straw return on crop yield,soil fertility and potassium fertilizer substitution in maize-rice cropping system were studied.The main findings of this experiment are as follows:?1?Double seasons straw return in maize-rice cropping system significantly increased dissolved organic carbon?DOC?,microbial biomass carbon?MBC?,mineral nitrogen(N_min),available phosphorus and available potassium in the 0-10 cm and10-20 cm soil layers.Compared with the single-season straw return treatment,the double seasons straw return had significantly higher content of DOC,MBC,N_min,available phosphorus and available potassium.Compared with the maize straw incorporated to the field treatment?Msr-Rs?,the DOC,MBC,N_min available phosphorus and available potassium in maize straw covering on the field treatment?Msc-Rs?were significantly increased by 5.3%-9.7%,2.6%-14.3%,4.2%-19.2%,1.4%-15.9%and 2.4%-10.1%.Straw return also significantly increased soil urease,cellulase,invertase and phosphatase activities in the 0-10 cm and 10-20 cm soil layers.Compared with Msr-Rs treatment,Msc-Rs treatment significantly increased soil urease,cellulase,sucrase and phosphatase activities.?2?Double seasons straw return in maize-rice cropping system significantly increased soil quality index.Compared with the no straw return treatment,straw return treatment reduced the soil bulk density and p H,and significantly increased the soil reducing substance and soil quality index.Straw return significantly increased crop yields and biomass.Compared with the control?CK?,M0Rs,Msr-Rs and Msc-Rs annual yields significantly increased by 2.5%-9.6%,8.8%-18.2%,and2.8%-12.9%,the annual biomass increased by 10.1%-12.3%,0.1%-6.0%and6.9%-16.1%,respectively.?3?Double seasons straw return with potassium fertilizer application in maize-rice cropping system significantly increased crop yield,biomass,potassium uptake and potassium utilization rate,at the same time,the differences in experiment increased with time.Compared with comtrol?CK?,Sr K33 and Sr K67 treatments increased annual yield by 8.5%-11.5%and 11.5%-16.0%.Meanwhile,Sr K33 and Sr K67treatments significantly increased biomass,potassium utilization efficiency,and apparent recovery of potassium in maize-rice cropping system.Based on the yields change of straw return treatment,the two seasons straw return in maize-rice rotation can replace about 47%chemical potassium fertilizer.?4?Double seasons straw return with potassium fertilizer application in maize-rice cropping system significantly affected SOC and available potassium,changed Q/I?capacity/strength?and their parameters which increased soil adsorption K capacity.Compared with no straw return treatment,straw return treatment significantly increased 0-10 cm and 10-20 cm soil layers SOC and available potassium contents.Straw return and potassium application increased the soil-?K₀and CR₀^K,and decreased PBC_e^K values,this means the soil had increased potassium easy-release pool and supply capacity,and decreased the soil adsorption capacity.The data showed that Sr K67 treatment had the strongest potassium supply capacity,and the weakest potassium adsorption capacity.In summary,after 2 years maize-rice rotation,our study find that double seasons straw return and maize straw covering on the field measure can effectively improve soil fertility.Meanwhile,under the two seasons straw return condition,reducing the application of 33%and 67%potash also can meet the potassium that crop demand.Straw return could improve soil fertility through improving soil carbon composition,N_min,available potassium,available phosphorous and soil enzymes.Reduced 67%potassium fertilizer can meet the demand for potassium in crops in a short period of time,which consumes a large amount of potassium in soil.Reduced 33%potassium fertilizer can maintain the high potassium supply capacity in soil and also meet the demand for potassium in the crop.Therefore,reduced 33%potassium fertilizer and two seasons straw return measure is an effective measure to improve soil fertility,converse fertility and maintain ecological balance in the long term.The long term potassium fertilizer reduction and straw return on soil needs further research and verification.