优化氮肥用量和基追比例提高红壤性水稻土肥力和双季稻氮素的农学效应

Optimization of nitrogen rate and base and topdressing ratio to improve agronomic soil fertility and use efficiency of nitrogen in rice

【目的】优化氮肥用量和基追比例是实现氮肥减施和提高肥料利用率的重要途径。本研究在南方典型双季稻种植区进行定位试验,通过对土壤肥力与氮素农学效益进行综合评价,以期提出适合当地土壤和水稻种植条件的氮肥减施模式。【方法】以南方典型红壤区双季稻种植体系为研究对象,于2014~2015连续进行了4季大田定位试验,设处理:1)不施氮肥(T1);2)当地农民习惯施氮(T2),早稻、晚稻各施N 165和195 kg/hm^2,基肥∶蘖肥∶穗肥比分别为60∶40∶0、40∶30∶30;3)在T2处理基础上减施氮肥20%(T3),即早稻施N 135 kg/hm^2,晚稻施N 165 kg/hm^2,基肥∶蘖肥∶穗肥比均为40∶30∶30,并以20%有机氮代替普通化肥氮。分析了成熟期水稻产量和植物样氮素含量,测定了0—20 cm土壤微生物量碳、氮含量,土壤p H、有机质、全氮、速效钾和有效磷等理化指标,计算了累计氮肥利用率和氮肥农学效率,分别利用内梅罗指数法和灰色关联度法综合评价了土壤肥力效应以及各施肥模式的综合效益。【结果】1)各处理土壤综合肥力指数(IFI)值由高到低为T3>T2>T1;与T2处理相比,优化氮肥用量和基追比例的T3处理IFI值提高2.34%,土壤微生物量碳含量提高了4.37%~25.39%,土壤微生物量氮含量提高了17.85%~29.24%(P<0.05)。2)与T2处理相比,2014–2015年T3处理累计氮肥农学效率显著提高了29.66%(P<0.05),累计氮肥表观利用率显著提高了28.82%(P<0.05);2014年各处理水稻总产量无显著差异,2015年水稻总产量T3处理比T2处理提高了5.26%,两年水稻总产量,T3处理提高了2.38%。3)对土壤养分指标、土壤微生物指标和氮素农学效率指标进行关联度分析,2014~2015年T3处理关联度最大,分别为0.9999和1.0000,在土壤肥力和氮肥农学效应综合评价中最优,表明优化氮肥用量和基追比例能够实现氮肥减施以及肥料利用率的提高。【结论】在当地农民习惯施氮的基础上减施20%化肥氮,以有机氮替代,并适当提高化肥氮在抽穗期的比例,能够保证土壤综合肥力的可持续性、氮素养分持续高效利用和水稻持续稳产。

【Objectives】Optimizing nitrogen fertilizer and topdressing ratio is an important way to reduce nitrogen fertilizer application and increase fertilizer use efficiency. In this paper, effects of different nitrogen fertilization treatments on soil fertility and nitrogen agronomic efficiency in the typical southern red paddy soil of double cropping rice system were investigated to provide a theoretical basis for sustainable and effective use of nitrogen fertilizers through a comprehensive evaluation. 【Methods】A 4-season and 2-year field experiment was conducted in the double cropping rice system with the typical southern red paddy soil of China from 2014 to2015. All treatments were designed as follows： 1） No N fertilizer： T1 treatment; 2） the farmers practice,T2treatment： N input in early and late rice was N 165 kg/hm^2 and N 195 kg/hm^2, the ratio of N in basal∶tillering∶heading stage was 60∶40∶0 and 40∶30∶30 respectively; 3） T3 treatment： the N input in early and late rice was N 135 and 165 kg/hm^2, the ratio of N in basal-tillering-heading stage was all 40∶30∶30,and 20% of chemical N was replaced by organic N. We measured the rice yield, rice nitrogen content, and the soil microbial biomass carbon and nitrogen,soil p H, organic matter, total N, readily available K and available phosphorus in 0–20 cm soil, calculated the cumulative nitrogen use efficiency and the agronomic efficiency of nitrogen fertilizer, and evaluated the soil fertility and fertilization modes by Nemero index and grey relational grade, respectively.【Results】1） The soil fertility results showed that the sequence from high to low of the integrated fertility indexes（IFI） values was T3 T2 T1, and the IFI value of the T3 treatment was 2.34% higher than that of T2 treatment. Compared with the T2 treatment,the contents of soil microbial biomass carbon and soil microbial biomass nitrogen in T3 treatment were enhanced by 4.37%–25.39% and 17.85%–29.24% separately. 2） The results of nitrogen agronomic efficiency showed that the nitrogen agronomic efficiency and apparent utilization of the T3 treatment from 2014 to 2015 were increased significantly by 29.66% and 28.82%（P〈0.05）,compared with the T2 treatment. The annual rice yield of T2 and T3 treatments had no significant difference in2014, while that of T3 treatment was improved significantly by 5.26%（P〈0.05） in 2015. The total rice yield of the T3 treatment from 2014 to 2015 was increased by 2.38% compared with the T2 treatment. 3） Based on the correlation degree analysis of the soil nutrient index, soil microbial index and nitrogen agronomy effect index, the correlation degrees of the T3 treatment in 2014 and 2015 were 0.9999 and 1.0000 respectively, which were the highest and indicated it was the best in the comprehensive evaluation of the agronomic effects on nitrogen fertilizer and the effect on soil fertility. The result showed that optimized nitrogen application rate and topdressing ratio could improve nitrogen fertilizer application and fertilizer utilization efficiency. 【Conclusions】The results of the 4-season and 2-year field experiment showed that 20% chemical nitrogen fertilizer less than local farmers practice and 20% nitrogen of the organic manure replaced the chemical nitrogen fertilizer and increasing the proportion of nitrogen fertilizer in heading stage could ensure the sustainability of soil fertility, nitrogen utilization efficiency and rice yield effectively.