| Huang-Huai-Hai Plain is the main producing region of wheat and maize,in which annual crop straw yield is over 200 million tons and more than 30%of straw is thrown away or burned on the field.Straw returning to fields is an effective way to utilize straw resource,which plays an important in improving soil fertility and governing of environmental pollution.However,conventional straw returning has some problems,such as the poor contact between soil and straw,the decline of straw decomposition rate,the reduction quality of crop seedlings and yield.The problems greatly limited the widespread application of straw returning in agricultural production.In order to resolve the problems and improve the utilization of crop straw,our group put forward a new way of straw incorporation by directly improving straw property.It was that the maize straw was granulated using a straw granulated machine and then added to soils.Granulated straw had high bulk density and small volume.The morphological change of straws greatly improved the distribution of residue material in soil,which could alter the straw decomposition rate and the process of soil fertility,but it is still unclear the effects of straw granulated incorporation on soil fertility,carbon sequestration ability and the process of crops growing.Therefore,a laboratory incubation experiment and a consecutive 3-year micro-field experiment from October 2013 to October 2016 were carried out to study the decomposition rate and nutrient release of chopped maize straw and granulated maize straw,and to elucidate the process of soil fertility,crop development and growth,and carbon emission characteristics of straw incorporation management in a winter wheat-summer maize double cropping system in Huang-Huai-Hai Plain.There were four treatments including in this paper:no straw incorporation,open field burning,conventional chopped straw incorporation and straw granulated incorporation.The main results were as follows:（1）Granulated straw increased the bulk density of straw,decreased the contents of cellulose,hemicellulose and lignin,accelerated straw decomposition and nutrient release,and finally decreased the duration of straw decomposition.The bulk density of the granulated straw（Φ=4 mm,length 4-6 cm）had 19.40 and 8.44 times than the conventional chopped straw（length 6-10 cm）and the chopped straw（length 3-5 cm）.This improved the contact between straw and soil due to the small volume.The granulated straw decreased the contents of cellulose,hemicellulose and lignin by 7.78%,30.80%and 10.06%in relative to the chopped straw,which accelerated straw decomposition.The average decomposition rate of the granulated straw in the rapid decomposition stage was 67.67 mg·d-1,which was 31.68%higher than that of the chopped straw.The rate of the granulated straw in the slow decomposition stage was about 17.21 mg·d-1.It was decreased by 2.63%than that of the chopped straw.After 300 days,the decomposition rate of granulated straw reached about 80.81%and significantly increased by 12.03%in comparison with chopped straw.According to the curve fitting,the time required for decomposition of 50%and 100%of the granulated straw reduced 30 days and 14 days in relative to the chopped straw.In addition,the granulated straw significantly increased the nutrient release rates throughout the incubation period,and there was a statistically significant difference in the earlier 60 days.After 300 days,the cumulative amount of carbon and nitrogen released from the granulated straw was 12.87%and 17.20%higher than that of the chopped straw.（2）The application of straw granulated incorporation significantly increased the concentrations of soil organic carbon（SOC）,dissolved organic matter（DOC）and available nitrogen（AN）in 0-20 cm layer.Compared with no straw incorporation and open field burning treatments,straw incorporation could increase the soil nutrient contents in 0-60 cm layer,and the increase of soil nutrient contents under the straw granulated incorporation were much higher,especially the contents of SOC,DOC and AN in 0-40 cm layer.Compared with the conventional chopped straw incorporation treatment,the SOC contents in 0-20 cm layer at maturity of the first wheat and first maize under the straw granulated incorporation treatment significantly increased by 8.24%and 5.02%,the DOC contents enhanced by 21.19%and 11.47%,and the AN contents increased by 6.12%and 11.10%.Meanwhile,the differences in the content of SOC,DOC and AN in 20-40 cm layer among treatments were similar to these in 0-20 cm layer.Compared with the conventional chopped straw incorporation treatment,the SOC content in 20-40 cm layer at the maturity of first wheat and first maize under the straw granulated incorporation treatment significantly increased by 4.51%and 3.34%,the DOC contents by 12.04%and 13.37%,and the AN contents by 4.27%and 5.53%.The correlation analysis indicated that both SOC and DOC had significantly positive correlated with AN,AP and AK,and the correlation coefficient was decreased with depths.Subsequently,integrated evaluation of soil fertility using principal component analysis indicated that the comprehensive soil amendment of straw incorporation was better than that of no straw incorporation and opening field burning treatments,and the amendment under the straw granulated incorporation treatment was much better than that under the conventional chopped straw incorporation treatment,and there was significant difference at the first wheat maturity.（3）Straw granulated incorporation significantly increased soil respiration rate and cumulative CO2 emission,but it had higher potential capacity of soil carbon sequestration potential because of highest net primary productivity.The soil water content in 0-10 cm layer,soil respiration rate and the cumulative CO2 emission under the straw granulated incorporation treatment during crop growing seasons increased by 0.99%-14.09%,0.35%-28.72%and 0.22%-21.02%than those under the other treatments,which resulted in a decline of the temperature sensitive coefficient of soil respiration rate.Compared with the conventional chopped straw treatment,the straw granulated incorporation promoted carbon emission,especially in the fisrt year of straw incorporation.The average rate of soil respiration and the cumulative CO2 emission during the fisrt wheat growing season under the straw granulated incorporation treatment significantly increased by 14.87%and 8.83%,and the values of the same indicators during the fisrt maize growing season increased by 1.47%and1.66%,respecially.However,the potential capacity of soil carbon sequestration under the straw granulated incorporation treatment significantly increased by 8.16%in comparison to the conventional chopped straw incorporation treatment because the above-ground biomass of wheat and mazie was 9.85%and 6.55%higher than that under the conventional chopped straw incorporation treatment.（4）Straw granulated incorporation guaranteed seedling emergence of the following crop and significantly increased the number and percentage of effective tillers.Meanwhile,it improved the leaf photosynthetic performance at late growth stage and increased dry matter accumulation,promoted translocation and distribution into the kernels and finally increased grain yield.Compared with the conventional chopped straw treatment,the straw granulated incorporation treatment markedly increased number of basic seedlings by 19.39%,promoted effective tiller development,and significantly increased effective spike rate of tiller and effective tiller number by 4.92%and 16.64%.Meanwhile,leaf area index,chlorophyll content and net photosynthetic rate of leaf at filling stage were also significantly elevated.This contributed to increase the above-ground biomass and transportation amount from vegetative organs to grain.The grain yields of wheat and maize under the straw granulated incorporation treatment increased by 10.71%and 3.42%.Further analysis found that the positive correlation between the first wheat yield and the number of effective tillers reached a significant level.However,the maize and wheat yield of the rest time after straw application were a positive correlation with grain weight and grain number per ears.（5）Straw granulated incorporation had maximum comprehensive benefit in agricultural production.The grey relational analysis results showed that comprehensive benefit under the straw incorporation treatments were much higher than that under the no straw incorporation and open burning field treatments.Moreover,the straw granulated incorporation treatment performed at a higher level than the conventional chopped straw treatment.In conclusion,granulated straw incorporation improved the contact between soil and straw,and significantly increased the effective spike number of crop.Meanwhile,it accelerated the decomposition and nutrient release of maize straw,improved soil fertility in the short time,promoted crop development and growth and enhanced leaf photosynthetic performance of wheat and maize.The improvement of photosynthetic characteristics contributed to the increase of above-ground dry matter accumulation and transportation amount from vegetative organs to grain to increase grain yield.Furthermore,it had a much higher potential capacity of soil carbon sequestration.Therefore,the application of straw granulated incorporation could serve as an effective candidate for the application of straw returning in Huang-Huai-Hai Plain. |
