不同施肥模式下轮作制度引起的土壤磷素有效性变化及其影响因素

【目的】探究不同轮作体系对土壤磷素有效性的影响,评估不同轮作体系土壤磷素活化潜力,为农田磷素高效利用提供科学依据。【方法】试验于2018—2020年在江苏省如皋市农业科学研究所开展,设置水稻-小麦（R-W）、水稻-油菜（R-O）、水稻-包菜（R-C）、水稻-闲田（R-F）4个轮作模式,每种轮作模式下设置3种施肥处理,分别为不施肥处理（CK）、不施磷处理（NK）、氮磷钾肥处理（NPK）。通过分析旱季和稻季成熟期不同施肥条件下地上部作物吸磷量、土壤磷组分含量、土壤微生物量及碱性磷酸酶活性等,明确不同水旱轮作体系下土壤磷素平衡及有效性变化规律,并探究其主要影响因素。【结果】NK处理下土壤磷素的严重失衡导致不同轮作体系土壤有效磷的补充存在差异。在NK处理下,R-O轮作可以保持较高的磷素输出以及促进土壤有效磷的补充。具体表现为NK处理下旱季R-O轮作体系下土壤活性磷相对含量较其他轮作体系低5.7%—7.3%,土壤中等活性磷和稳定性磷相对含量分别较其他轮作体系高4.2%—6.4%和0.9%—1.9%。相比之下,NK处理下稻季土壤中等活性磷相对含量较其他轮作体系高0.5%—3.0%,活性磷和稳定性磷相对含量则分别较其他轮作体系低0—1.5%和0.2%—2.3%。NK处理下,R-O轮作土壤微生物量碳磷比在旱季和稻季均相对较小,且在稻季时显著低于R-W轮作。土壤微生物量氮磷比也具有类似的规律。R-O轮作土壤碱性磷酸酶在旱季和稻季均保持较高活性。路径分析模型表明,磷素携出量（-0.53）和碱性磷酸酶（-0.51）分别对旱季和稻季土壤有效磷含量的贡献最高。【结论】在土壤磷素相对亏缺时,水稻-油菜轮作可以通过在旱季释放更多的碱性磷酸酶和调节稻季的土壤微生物量碳磷比,进而促进微生物活化非活性态磷库以补充活性态磷库,以保证在不影响磷素输出的情况下维持土壤有效磷含量的相对稳定。

Influence of Typical Rotation Systems on Soil Phosphorus Availability Under Different Fertilization Strategies

【Objective】 In order to provide a scientific basis for the efficient utilization of phosphorus in farmland, the effects of different rotation systems on the availability of soil phosphorus were explored to evaluate the potential of soil phosphorus activation in different crop rotation systems. 【Method】 The experiment was conducted at Rugao Institute of Agricultural Sciences, Jiangsu Province from 2018 to 2020. Four paddy-upland rotation systems in the experiment included rice-wheat (R-W), rice-oilseed rape (R-O), rice-cabbage (R-C), and rice-fallow (R-F) rotation. Three fertilization treatments under each rotation system were applied, including no fertilization treatment (CK), no phosphate treatment (NK), and NPK fertilization treatment (NPK). The variation patterns and main influencing factors of soil phosphorus balance and availability under different paddy and upland rotation systems were clarified by analyzing the phosphorus uptake by aboveground crops, soil phosphorus fraction contents, soil microbial biomass and soil alkaline phosphatase activity under different phosphorus application conditions in dry season and rice season maturity. 【Result】 The severe imbalance of soil phosphorus under NK treatment resulted in differences in the supplement of soil available phosphorus in different rotation systems. Under NK treatment, R-O rotation could maintain a higher phosphorus output and promote the replenishment of soil available phosphorus. Specifically, the relative content of soil labile phosphorus in R-O rotation in dry season under NK treatment was 5.7%-7.3% lower than that in other rotations, and the relative content of soil moderately labile phosphorus and stable phosphorus were 4.2%-6.4% and 0.9%-1.9% higher than that in other rotations, respectively. However, the relative content of soil moderately labile phosphorus in R-O rotations under NK treatment in rice season was 0.5%-3.0% higher than that under other rotations, and the soil labile phosphorus and stable phosphorus were 0-1.5% and 0.2%-2.3% lower than that under other rotations, respectively. Under NK treatment, the soil microbial biomass C/P ratios of R-O rotation was relatively small in both dry season and rice season, and it was significantly lower than that under R-W rotation in rice season. The soil microbial biomass N/P ratios also had a similar trend. But the soil alkaline phosphatase activity of R-O rotation maintained a high level in both dry season and rice season. The path analysis model showed that the phosphorus accumulation (-0.53) and the soil alkaline phosphatase (-0.51) had the most contribution to the soil available phosphorus in dry season and rice season, respectively. 【Conclusion】 When the soil phosphorus was relatively imbalance, the rice-oilseed rape rotation released more alkaline phosphatase in dry season and regulated the soil microbial biomass C/P ratio in rice season, which was conducive to promoting the activation of the non-labile phosphorus by microorganisms to supplement the labile phosphorus, so as to ensure the relative stable of soil available phosphorus content without affecting phosphorus output.