水稻油菜轮作下稻草还田和钾肥对土壤团聚体及钾素分布的影响

目的 通过田间定位试验探究水稻-油菜轮作和水稻-冬闲模式下不同施肥措施对稻田土壤团聚体特性及团聚体钾素分布的影响，为我国南方水旱轮作区钾素资源可持续利用提供依据。方法 利用始于2016年不同轮作模式钾肥定位试验，选取CK（F）（不施肥和冬闲）、NPK（F）（氮磷钾肥和冬闲）、NPK（R）（氮磷钾肥和冬种油菜）、NPK（SR+R）（氮磷钾肥配稻草还田和冬种油菜）、NP50%K（SR+R）（氮磷减钾50%配稻草还田和冬种油菜）5个处理，在试验第3年（2019年）于油菜收获后取0—20 cm土层土样，分析土壤团聚体组分以及团聚体组分中交换性钾和非交换性钾含量变化，并进一步探讨土壤团聚体稳定性及团聚体组分中钾素的分布规律。结果 （1）所有处理均以<0.053 mm团聚体组分最高。与NPK（F）相比，NPK（R）处理提高了1—2、0.5—1、0.25—0.5 mm团聚体的比例，增幅为26.2%—82.6%，土壤团聚体的稳定性增加，>0.25 mm团聚体组分比例、平均重量直径（MWD）和平均几何直径（GMD）显著提高了30.6%、31.2%和82.0%。水稻-油菜轮作模式下，稻草还田配施化肥（NPK（SR+R））比施化肥处理（NPK（R））显著提高了>2 mm团聚体比例，增幅为69.7%。（2）所有处理土壤各团聚体组分中交换性钾含量随团聚体粒级的减小逐渐降低，水稻-油菜轮作模式下，稻草还田配施化肥（NPK（SR+R））比施化肥处理（NPK（R））显著提高了所有粒级团聚体组分的交换性钾含量，增幅为22.2%—46.0%。相比较NPK（SR+R），减钾处理（NP50%K（SR+R））显著降低了>0.5 mm团聚体中交换性钾的含量，降幅为19.4%—20.6%。与水稻-冬闲下的化肥处理（NPK（F））相比，水稻-油菜轮作下3个施肥处理均降低了团聚体中的非交换性钾含量。（3）所有处理以<0.053 mm团聚体中钾对全土钾的贡献率最高。水稻-油菜轮作（NPK（R））比水稻-冬闲（NPK（F））显著提高了1—2和0.5—1 mm团聚体中钾对全土钾的贡献率，增幅分别为82.6%、52.1%（交换性钾）和105.5%、36.9%（非交换性钾）。结论 水稻-油菜轮作可提高MWD、GMD、大团聚体比例和大团聚体中钾对全土钾的贡献率，改善土壤结构。在该轮作模式下稻草还田配施化肥可提高所有粒级团聚体中交换性钾含量，改善稻田土壤钾素供应，但水稻-油菜轮作因需钾量高而降低了团聚体中的非交换性钾含量，应适当增加钾肥投入。

Effects of Straw Returning and Potassium Fertilizer on Soil Aggregate and Potassium Distribution Under Rapeseed-Rice Rotation

【Objective】 The study aimed to explore effects of different fertilization on paddy soil aggregate characteristics and potassium distribution under rapeseed-rice rotation and winter fallow by the located experiment test. It was hoped that the study would provide a basis for the sustainable utilization of potassium resources in paddy-upland rotation areas of Southern China. 【Method】 Based on the location experiment of potassium fertilizer in different rotation patterns started in 2016, five treatments were selected, including CK(F) (no fertilization and winter fallow), NPK(F) (NPK fertilizer and winter fallow), NPK(R) (NPK fertilizer and winter rapeseed), NPK (SR+R) (NPK fertilizer with rice straw returning and winter rapeseed), and NP50%K (SR+R) (50% reduction of K fertilizer with rice straw returning and winter rapeseed). The soil samples were collected from the 0-20 cm soil layer of each treatment after rape harvest of the third year for analysis of physical and chemical properties, such as soil aggregates distribution, and exchangeable and non-exchangeable potassium content variation in soil aggregates. The stability of soil aggregates and the distribution of potassium in aggregates were further investigated..【Result】 The soil aggregate fractions of all treatments was the highest in <0.053 mm. Compared with NPK(F), NPK(R) increased the proportion of aggregates of 1-2 mm, 0.5-1 mm and 0.25-0.5 mm by 26.2%-82.6% under the same fertilization treatment. Also the stability of soil aggregates was increased, the proportion of aggregates of >0.25 mm, mean weight diameter (MWD), and geometric mean diameter (GMD) were significantly increased by 30.6%, 31.2% and 82.0%, respectively. Under rapeseed-rice rotation, the proportion of aggregates of >2 mm was increased under NPK(SR+R), which was 69.7% higher than that under NPK(R). The exchangeable potassium content in soil aggregates decreased with decreasing particle size under all treatments. NPK(SR+R) significantly increased exchangeable potassium content in all aggregate fractions by 22.2%-46.0% compared with NPK(R) under rapeseed-rice rotation. NP50%K(SR+R) significantly reduced the exchangeable potassium content in aggregates of >0.5 mm by 19.4%-20.6% than NPK(SR+R). Compared with NPK(F), three fertilization treatments under rapeseed-rice rotation all reduced the non-exchangeable potassium content in aggregate fractions. Under all treatments, the contribution rate of different fractions of soil aggregates to the bulk soil in potassium was the highest in <0.053 mm. Compared with NPK(F), NPK(R) significantly increased the contribution rates of 1-2 mm and 0.5-1 mm aggregates to bulk soil in potassium by 82.6%, 52.1% (exchangeable potassium ) and 105.5%, 36.9% (non-exchangeable potassium), respectively.【Conclusion】 The rapeseed-rice rotation could increase MWD, GMD, macroaggregate proportion and the contribution rate of macroaggregate to the bulk soil in potassium and improve soil structure. Under this rotation pattern, the chemical fertilizer combined with rice straw returning could increase the exchangeable potassium content in all aggregate fractions, which improved the potassium supply in paddy soil. However, the rapeseed-rice rotation reduced the content of non-exchangeable potassium in soil aggregates due to high potassium demand, and the input of potassium fertilizer should be appropriately increased.