我国水稻秸秆钾资源分布及其还田对土壤钾平衡的重要性

Distribution of rice straw potassium resources across China and the importance of rice straw incorporation to soil potassium balance

【目的】我国钾肥资源不足但秸秆资源丰富,有待科学高效循环利用。本研究估算了我国水稻秸秆钾养分的量和空间分布特征,为利用水稻秸秆还田保持土壤钾素平衡提供参考。【方法】本研究基于《中国农村统计年鉴》和其他文献资料数据,结合草谷比法对我国各省份不同季别水稻秸秆钾资源量及还田情景下的土壤钾输入量进行测算。【结果】2019年我国水稻秸秆钾(K_(2)O)养分总产量为493.9万t,其中早稻、晚稻和中晚稻秸秆钾养分量的占比分别为13.1%、14.6%和72.4%。不同稻区的水稻秸秆钾资源量占总量的比例为:长江中游(33.4%)˃长江下游(21.7%)˃西南(15.3%)˃东北(13.1%)˃华南(12.8%)˃华北(3.7%)。早稻和晚稻秸秆钾养分主要源自湖南(25.2%和24.7%)、江西(23.8%和24.4%)、广东(18.6%和19.5%)及广西(17.2%和14.8%)。中晚稻秸秆钾养分资源在主产省区间的分布表现为:江苏(14.3%)˃黑龙江(12.9%)˃湖北(12.2%)˃四川(10.7%)˃安徽(10.5%)˃湖南(8.8%)。在双季稻主产省区湖南、江西、广东和广西,早稻秸秆还田可向土壤输入钾量分别为148.7、140.6、143.9和145.0 kg/hm^(2),早稻籽粒钾的携出量分别为25.6、24.2、24.8和25.0 kg/hm^(2);晚稻秸秆还田可向土壤输入钾量分别为153.4、145.3、146.3和131.1 kg/hm^(2),晚稻籽粒钾的携出量分别为30.3、28.7、28.9和25.9 kg/hm^(2);不施钾肥条件下,4个省区双季稻体系秸秆不还田的土壤钾素周年亏缺量分别为357.9、338.8、343.9和327.0 kg/hm^(2),秸秆还田后的土壤钾素周年亏缺量分别降至55.9、52.9、53.6和50.8 kg/hm^(2)。中晚稻主产区为东北、长江下游、长江中游和西南稻区,中晚稻秸秆钾养分资源量分别为125.8、203.8、201.1和189.0 kg/hm^(2),相应的籽粒钾携出量分别为32.6、29.4、29.0和27.3 kg/hm^(2),说明如果秸秆全部还田,可以提高土壤钾素盈余。【结论】我国70%以上的水稻秸秆钾养分资源来自于中晚稻,50%以上的水稻秸秆钾养分资源分布在长江中游和长江下游稻区。早稻和晚稻秸秆还田可以大大降低土壤钾素亏缺,而中晚稻秸秆全部还田则可以提升土壤钾素的年盈余量。

【Objectives】China is short in potassium resources but rich in rice straw,which contains sufficient potassium resources for recycling.Here,we assessed the quantity of straw K resources and spatial distribution for keeping the soil K balance in China.【Methods】Based on China Rural Statistical Yearbook and literature,we assessed the rice straw resources in different cropping seasons at provincial and regional levels.The straw K resources were calculated using the grain-to-straw ratio method.We assessed K input from rice straw incorporation and the contribution to soil K apparent balance.【Results】The total output of straw K resources was K_(2)O 4.939 million tons in 2019,with 13.1%,14.6%,and 72.4%recorded from early,late,and medium-late rice,respectively.The order of straw K resources distribution was Middle Yangtze River(33.4%)˃Lower Yangtze River(21.7%)>Southwest China(15.3%)>Northeast China(13.1%)>South China(12.8%)>North China(3.7%).Early and late rice were mainly cultivated in Hunan,Jiangxi,Guangdong,and Guangxi;the proportion of early and late rice straw K resources were 25.2%and 24.7%in Hunan,23.8%and 24.4%in Jiangxi,18.6%and 19.5%in Guangdong,and 17.2%and 14.8%in Guangxi.The medium-late rice was mainly cultivated in Jiangsu,Heilongjiang,Hubei,Sichuan,Anhui,and Hunan;the proportion of medium-late rice K resources in the provinces were 14.3%,12.9%,12.2%,10.7%,10.5%,and 8.8%,respectively.The annual K_(2)O inputs from early rice straw incorporation in Hunan,Jiangxi,Guangdong,and Guangxi were 148.7,140.6,143.9,and 145.0 kg/hm^(2).The corresponding K_(2)O removed by early rice grains were 25.6,24.2,24.8,and 25.0 kg/hm^(2),respectively.The K_(2)O inputs from late rice straw incorporation were 153.4,145.3,146.3,and 131.1 kg/hm^(2);the K_(2)O removed by late rice grains were 30.3,28.7,28.9,and 25.9 kg/hm^(2)in Hunan,Jiangxi,Guangdong,and Guangxi,respectively.Without K fertilization,the soil K apparent balance under the double rice system had a deficit of 357.9,338.8,343.9,and 327.0 kg/hm^(2)in Hunan,Jiangxi,Guangdong,and Guangxi,respectively.Straw incorporation reduced the deficits to 55.9,52.9,53.6,and 50.8 kg/hm^(2).The K_(2)O inputs by medium-late rice straw returning were 125.8,203.8,201.1,and 189.0 kg/hm^(2),and the K_(2)O removed by rice grains were 32.6,29.4,29.0 and 27.3 kg/hm^(2)in Northeast China,Lower Yangtze River,Middle Yangtze River,and Southwest China,respectively,indicating K surplus if the rice straw was fully returned to the field.【Conclusions】More than 70%of rice straw K resources exist in medium-late rice,and the Middle Yangtze River and Lower Yangtze River regions have the largest straw K resources in China.Early and late rice straw incorporation could reduce the soil K deficits,and the full incorporation of medium-late rice straw leads to a surplus of soil K.Therefore,rice straw incorporation is an important way of keeping soil potassium fertility in China.