长期施肥紫色水稻土磷素累积与迁移特征

【目的】探讨长期不同施肥对钙质紫色水稻土磷素累积与迁移的影响。【方法】以长期肥料定位试验不同施肥处理的土壤为研究对象,试验处理包括不施肥(CK)、氮肥(N)、氮磷肥(NP)、氮磷钾肥(NPK)、有机肥(M,鲜猪粪)、有机肥+氮肥(MN)、有机肥+氮磷肥(MNP)和有机肥+氮磷钾肥(MNPK)8种施肥方式,研究不同施肥处理条件下钙质紫色水稻土磷素平衡、累积和去向状况,以及不同施肥方式对耕层(0—20 cm)土壤全磷、有效磷演变规律及土壤剖面(0—100 cm)全磷、有效磷迁移特征。【结果】钙质紫色水稻土33年不施用磷肥(CK和N)作物籽粒和秸秆磷素携出总量为613.12 kg·hm-2,种苗、根茬、雨水及灌溉水带入土壤总磷量为106.61 kg·hm-2,长期不施用磷肥土壤磷素表现出亏缺状况,年亏缺量为15.35 kg·hm-2,且土壤磷含量随种植年限延续而下降,土壤全磷含量年均减少量为0.0011 g·kg-1、有效磷含量年均减少量为0.029 mg·kg-1;33年单施无机磷肥(NP和NPK)土壤磷素投入总量为1 880.03 kg·hm-2、作物携出磷量为1 275.40 kg·hm-2,有机肥处理(M和MN)土壤投入磷量为2 532.68 kg·hm-2、携出磷量为757.50 kg·hm-2;有机无机磷肥配施(MNP和MNPK)土壤投入和携出磷量分别为4 305.11和1 436.64 kg·hm-2;不同施肥处理土壤磷素投入量都明显高于作物携出量,导致单施无机磷肥、单施有机磷肥和有机无机磷肥配施处理土壤磷素年盈余量分别为18.32、53.79和86.92 kg·hm-2,年未知去向磷量分别为4.99、34.96和59.39 kg·hm-2,土壤全磷含量年增加量分别为0.015、0.0018和0.018 g·kg-1,有效磷含量年增加量分别为1.13、0.032和1.17 mg·kg-1。长期不施用磷肥钙质紫色水稻土全磷含量随土层深度增加而降低,土壤有效磷含量则相反;长期施用磷肥土壤全磷和有效磷含量在土壤剖面都呈现出上下层高、中间低的空间分布格局。施用无机磷肥土壤磷素可迁移至60—80 cm土层,施用有机磷肥或有机无机磷肥配施土壤磷素可迁移至100 cm以下;随着磷肥施用年限持续,土壤磷素迁移深度和迁移量将会更大,有机肥的施用促使磷素向土壤下层迁移。【结论】连续数年施用磷肥后,土壤磷含量达到一定水平时应考虑减少磷肥用量,减少因有机肥过量施用导致的磷素快速积累和淋失。

Characteristics of Phosphorus Accumulation and Movement in a Calcareous Purple Paddy Soil Profile as Affected by Long-Term Fertilization

【Objective】 The objective of this study is to investigate the effects of long-term fertilization on phosphorus (P) accumulation and movement in profile of a calcareous purple paddy soil. 【Method】 The ongoing experiment, initiated in 1981, consisted of eight treatments including CK (no fertilizer), nitrogen fertilizer (N), nitrogen and phosphorus fertilizers (NP), nitrogen, phosphorus and potassium fertilizers (NPK), pig manure (M), pig manure plus nitrogen fertilizer (MN), pig manure plus nitrogen and phosphorus fertilizers (MNP) and pig manure plus nitrogen, phosphorus and potassium fertilizers (MNPK) with four replications. Status of P balance, accumulation and fate, soil total P (TP) and Olsen-P at 0-20 cm soil depths, and P accumulation and distribution at 0-100 cm soil depths were measured to get better understanding of the impacts of different treatments on these parameter changes after 33 years in the calcareous purple paddy soil in the Southwest China. 【Result】 Results showed that 613.12 kg·hm^-2 of P in P omission treatments (CK and N alone) were absorbed by crop grain and straw after 33 years in the calcareous purple paddy soil. The P nutrient from seeds, stubble, rain and irrigation waters was about 106.61 kg·hm^-2 entered into the soil. Thus soil P became deficient when P was omitted from the fertilizer program (CK and N alone), giving an average deficit value of 15.35kg·hm^-2 of P nutrient. And the situation was worsened with time, changing of 0.0011 g·kg^-1 in TP and 0.029 mg·kg^-1 in Olsen-P annually. After 33-year different fertilizer treatments, two inorganic P treatments (NP and NPK) resulted in 1 880.03 kg·hm^-2 of total P inputs and 1 275.40 kg·hm^-2 of P uptake by crops. Total inputs of P were 2 532.68 kg·hm^-2 and P absorbed by crop was 757.50 kg·hm^-2 in two P-omitted organic manure treatments (M and MN). And P inputs and uptake were 4 305.11 and 1 436.64 kg·hm^-2 in the two P-added organic manure treatments (MNP and MNPK), respectively. Thus treatments amended with P and/or organic manure yielded annual balances of total P as 18.32, 53.79 and 86.92 kg·hm^-2, fate unknown P as 4.99, 34.96 and 59.39 kg·hm^-2. TP changing as 0.015, 0.0018 and 0.018 g·kg^-1 and Olsen-P as 1.13, 0.032 and 1.17 mg·kg^-1 for the two inorganic P treatments, the two P-omitted organic manure treatments and the two P-added organic manure treatments, respectively. The P omission treatments resulted in reduction of TP with depths downward the profile, while an opposite trend was observed for Olsen-P. P treatments, however, gave P distribution patterns of highs in the top and the bottom depths but lows in the middle layers. Addition of inorganic P fertilizers could transfer P down to the 60-80 cm soil profile, while addition of organic manure alone or in combination with inorganic P fertilizers could move P further down to more than 100 cm soil depths, suggesting that organic P was more mobile than inorganic P in the soil and susceptible to loss. 【Conclusion】When soil Olsen-P reaches to an adequate level (eg. 20 mg·kg^-1 as a critical value for most of cereal crops) after consecutive applications of P fertilizers for years, reduction in P rates, organic P in particular, should be considered to maintain or effectively lower soil P pool and to minimize P losses to environment.