稻田不同供钾能力条件下秸秆还田替代钾肥效果

【目的】研究稻田不同土壤供钾能力条件下，秸秆还田配施钾肥对水稻产量、地上部钾素累积量以及钾肥利用率的影响，为秸秆还田水稻钾肥合理施用提供科学依据。【方法】2011-2012年在鄂中、江汉平原和鄂东地区的10个县（市）选择不同供钾水平田块布置水稻试验。根据湖北省第二次土壤普查制定的速效钾分级标准，本文将土壤速效钾含量＞150 mg•kg-1的试验点如钟祥和宜城归为高钾供应能力土壤（1级水平），简称为高钾土壤，标记为High-K；土壤速效钾含量100-150 mg•kg-1的试验点如团风、仙桃、洪湖和枝江归为中钾供应能力土壤（2级水平），简称为中钾土壤，标记为Middle-K；土壤速效钾含量＜100 mg•kg-1的试验点如麻城、广水、鄂州和蕲春归为低钾土壤，标记为Low-K。试验共设6个处理，分别为：（1）CK（-K）；（2）+K；（3）+S；（4）S+1/3K；（5）S+2/3K；（6）S+K，其中K和S分别表示钾肥和还田秸秆，以此来考查当前推荐钾肥用量（K2O 75 kg•hm-2）对水稻的增产效果以及轮作模式下麦秆或油菜秸秆还田钾素对钾肥的替代作用。【结果】结果显示CK处理（-K），高钾、中钾和低钾土壤的稻谷产量分别为8 372、8 710和7 767 kg•hm-2，施钾和秸秆还田均可以不同程度地增加水稻产量和地上部钾素累积量。与CK相比，高钾、中钾和低钾土壤均以秸秆还田配施钾肥处理的增产效果最显著，增产量分别为633、1 098和814 kg•hm-2，增幅分别为7.7%、12.6%和12.5%；地上部钾素累积吸收增量分别为40.2、56.5和49.3 kg•hm-2，增幅分别为15.9%、21.3%和36.8%。在当前推荐钾肥用量条件下，秸秆还田会造成高钾土壤的钾肥吸收利用率下降，但可明显提高中钾和低钾土壤的钾肥吸收利用率；同时秸秆还田也会显著降低高钾土壤的钾肥农学利用率，但对中钾和低钾土壤的钾肥农学利用率没有明显影响。同钾肥利用率相比，钾素利用率均有所降低，但中钾土壤和低钾土壤的钾素利用率要显著高于高钾土壤的钾素利用率。通过对秸秆还田条件下钾肥用量与增产率、地上部钾素累积增幅的相关性分析得出高钾土壤和中钾土壤的推荐钾肥用量偏高。根据线性加平台肥效模型拟合得出，在秸秆还田条件下，高钾土壤田块（速效钾含量＞150 mg•kg-1）适宜钾肥用量平均为38.2 kg•hm-2，比推荐用量减少49.1%；中钾土壤田块（速效钾含量100-150 mg•kg-1）适宜钾肥用量平均为60.0 kg•hm-2，比推荐用量减少20.0%；而低钾土壤田块（速效钾含量＜100 mg•kg-1），增产效果显著，推荐钾肥用量不足。【结论】因此，短期秸秆还田条件下，高钾和中钾土壤田块，秸秆还田钾素可不同程度地替代部分化学钾肥施用；而低钾供应田块推荐用量略显不足，增施钾肥仍有较大的增产空间。

Effect of Straw Incorporation Substitute for K-Fertilizer Under Different Paddy Soil K Supply Capacities

【Objective】In order to provide a scientific basis for crop residue management and K fertilization, the effect of straw incorporation plus K-fertilizer on yield of rice, potassium (K2O) accumulation amount of shoots and potassium efficiency under different paddy soil potassium levels was studied. 【Method】A series of field trials were carried out to study the effect of recommended rate of potassium (K2O 75 kg•hm-2) on rice production and whether straw potassium could replace chemical potassium under wheat-rice/rape-rice cropping systems in selected 10 counties in Ezhong, Jianghan plain and Edong regions during 2011-2012. According to the second national soil census in Hubei province, trial sites (available K content >150 mg•kg-1), Zhongxiang (ZX) and Yicheng (YC) were classified as high potassium supply capacity soils, marked as high-K; the test points (available K content 100-150 mg•kg-1), Tuanfeng (TF), Xiantao (XT), Honghu (HH) and Zhijiang (ZJ) were classified as middle potassium supply capacity soils, labeled as Middle-K; the test points (available K content <100 mg•kg-1), Macheng (MC), Guangshui (GS), Ezhou (EZ) and Qichun (QC) were normalized to low potassium supply capacity soil, labeled as Low-K. The field experiment was carried out in a randomized block design, including six treatments with three replications. The designed treatments were CK (-K), +K, +S, S+1/3K, S+2/3K, and S+K, where K and S denoted K fertilizer and straw, respectively. 【Result】The results showed that the yield of CK treatment for high-K, middle-K and low-K soil were 8372, 8710 and 7767 kg•hm-2, respectively. However, the K-fertilizer and straw returning to field could increase yield of rice and K accumulation amount of shoots at varying degrees. The straw incorporation with K-fertilizer treatment got the best effect compared with CK treatment. The increased yields were 633, 1098 and 814 kg•hm-2, respectively and the yield increase rates were 7.7%, 12.6% and 12.5%, respectively for high-K, middle-K and low-K soils. The increased K accumulations were 40.2, 56.5 and 49.3 kg?hm-2 and the K increase rates were 15.9%, 21.3% and 36.8%, respectively. Straw incorporation could reduce the KfRE (K fertilizer recovery efficiency) of high-K soil, but increase the KfRE of middle-K and low-K soils, significantly. Meanwhile, straw returning to field also lowered the KfAE (K fertilizer agronomic efficiency) of high-K soil, but enhanced the KfAE of others. Compared with KfRE and KfAE, the KRE and KAE (K efficiency of straw-K with chemical-K) were reduced, but the KRE and KAE of middle-K and low-K soils were obviously higher than those of high-K soil. Under the straw returning to field condition, the correlation analysis between increase of yield, K accumulation and K-fertilizer amount indicated that the recommended rate of potassium was more than the actual demand of rice growth in high-K soil and middle-K soil. Using the fertilizer efficiency model and considering straw returning to field, the optimal amount of K-fertilizer was 38.2 kg•hm-2 for high-K soil (available potassium content>150 mg•kg-1), which was 49.1% less than the recommended amount in Hubei province. In the same way, the optimal amount of K-fertilizer was 60.0 kg•hm-2 for middle-K soil (available potassium content 100-150 mg•kg-1), which was 20.0% less than the recommended amount. Whereas for low-K soil (available potassium content<100 mg•kg-1), the current recommended amount of K-fertilizer was deficient. 【Conclusion】 It was concluded that straw potassium could replace partial chemical potassium for higher soil K supply, but insufficient for lower soil K supply if more grain wants to be produced in short-term of straw incorporation.