长期施肥红壤钾素在有机无机复合体中的分布

【目的】土壤中的有机无机复合体是承载土壤养分的重要结构单元,土壤钾素含量的变化反映在不同粒级有机无机复合体中。本研究选用始于1990年(祁阳)和1986年(进贤)的旱地红壤长期定位试验,研究长期不同施肥对土壤交换性钾、非交换性钾、全钾在不同粒级有机无机复合体中分布的影响。【方法】祁阳和进贤试验点均选择不施肥(CK)化学氮、磷肥配施(NP)、NP基础上施用化学钾肥(NPK)及NPK基础上配施有机肥(NPKM)四个处理,采集0-20 cm深度的土壤样品通过Stokes定律计算各粒级复合体沉降速率,采用虹吸管法分离出不同粒级有机无机复合体。采用1.0 mol/L中性醋酸铵浸提土壤交换性钾,1.0 mol/L沸硝酸浸提土壤非交换性钾,氢氧化钠710℃提取土壤全钾钾离子浓度采用火焰光度计测定。【结果】两试验点土壤96.4%~98.9%的交换性钾、87.9%~96.7%的非交换性钾和95.1%~96.7%的全钾存在0~50μm粒级复合体中,尤其2μm粒级复合体是三种形态钾素的主要贮存库76.3%~92.3%的交换性钾、45.8%~73.7%的非交换性钾和49.4%~70.6%的全钾集中在该粒级。两试验点NP处理与CK相比,2μm粒级复合体中非交换性钾含量降低5.4~8.3 mg/kg.降低幅度为8.2%~16.3%。施钾肥主要改变2 m粒级复合体中交换性钾和非交换性钾含量进贤NPK与NP处理相比分别增加36.7和9.5 mg/kg,增加幅度分别为64.5%和15.7%;而NPKM处理则较NP处理分别增加147.4和91.2 mg/kg增幅分别为258.9%和151.1%。祁阳NPK与NP处理相比,2μm粒级复合体中交换性钾和非交换性钾含量分别增加52.9和20.3 mg/kg增加幅度分别为104.9%和47.6%;NPKM与NP处理相比分别增加219.5和41.3 mg/kg增幅分别为435.9%和96.9%。长期施肥对两试验点各粒级复合体中全钾含量的影响不大。2、2~10及10~50μm粒级复合体三种形态钾素含量较高,是供给植物生长的主要钾源,其中2μm粒级复合体中交换性钾、非交换性钾含量与产量之间均存在显著正相关关系(P0.05)。【结论】2μm粒级复合体是土壤钾素的主要贮存库。在长期不施钾肥条件下土壤2μm粒级复合体中交换性钾和非交换性钾含量降低,施钾有利于该粒级复合体中交换性钾和非交换性钾积累。旱地红壤2、2~10及10~50μm粒级复合体钾素含量高且与产量之间存在显著的正相关关系是植物钾素主要供源。

Distribution of potassium in the organo-mineral complexes of red soils under long-term fertilization

【Objectives】 Soil organo-mineral complexes contain most of soil nutrients that have become a most important part of soil nutrients. Change of soil potassium contents affects the contents of potassium in different sizes of organo-mineral complex. So long-term experiments of red soil started from 1990 (Qiyang) and 1986 (Jinxian) were carried out to investigate distribution of exchangeable, non-exchangeable and total potassium (K) in different sizes of organo-mineral complex. 【Methods】 The soil samples of 0-20 cm depth were collected from the four treatments in the long term experiment at both sites: No fertilization (CK), mixed application of chemical nitrogen and phosphorus fertilizer (NP), mixed application of NP combined with chemical potassium fertilizer (NPK), mixed application of NPK combined with manure (NPKM) treatments. Stokes law was used to calculate sedimentation rates of different sizes of organo-mineral complex which were separated using siphon. The soil exchangeable, non-exchangeable and total potassium were determined. 【Results】 In the two sites, 96.4%-98.9% of the exchangeable K, 87.9%-96.7% of the non-exchangeable K and 95.1%-96.1% of the total K are in 0-50 m sizes of organo-mineral complex. Especially, 76.3%-92.3% of the exchangeable K, 45.8%-73.7% of the non-exchangeable K and 49.4%-70.6% of the total K at both sites are mainly in 2 m size complex. Comparing with CK, the contents of non-exchangeable K under NP are decreased by 5.4 to 8.3 mg/kg, and the decreased ratios are from 8.2% to 16.3% at both sites. The contents of the exchangeable and non-exchangeable K in 2 m complex are mostly influenced by the potassium fertilization, and compared with NP at Jinxian site, the contents under the treatments of NPK are increased by 36.7 and 9.5 mg/kg with the increased ratios of 64.5% and 15.7%, and the contents under the treatments of NPKM are increased by 147.4 and 91.2 mg/kg with the increased ratios of 258.9% and 151.1%. Compared with NP at Qiyang site, the contents of exchangeable and non-exchangeable K under the treatment of NPK are increased by 52.9 and 20.3 mg/kg with the increased ratios of 104.9% and 47.6%, and the contents under the treatment of NPKM are increased by 219.5 and 41.3 mg/kg with the increased ratios of 435.9% and 96.9%. The contents of total K in different sizes of organo-mineral complex have little changes under the long-term fertilization. The main sources of K which plants uptake are 2, 2-10 and 10-50 m sizes of organo-mineral complex. Both the exchangeable and non-exchangeable K in 2 m size of organo-mineral complex have significant positive correlations with crop yield (P0.05). 【Conclusions】 The organo-mineral complex of 2 m is the major K pool. The long-term fertilization without K induces the decreases of the contents of exchangeable and non-exchangeable K in 2 m size of complex, while K fertilization is beneficial to increasing the contents of exchangeable and non-exchangeable K in this size of organo-mineral complex. The organo-mineral complexes of 2, 2-10 and 10-50 m contain most of the potassium, which are the main sources of potassium absorbed by plants. There are positive correlations between the contents of potassium in different sizes of organo-mineral complex and crop yield in red soil.