长期不同施肥红壤磷素特征和流失风险研究

为探索长期施肥对红壤磷素吸附固持的影响,分析不同施肥土壤磷流失风险及影响因素。在南方丘陵区红壤上开展了持续25年的长期定位试验,处理包括:不施肥(CK)、施氮肥(N)、施磷肥(P)、施钾肥(K)、施氮磷钾肥(NPK1)、施2倍量氮磷钾肥(NPK2)、单施有机肥(OM)和氮磷钾配施有机肥(MNPK)。研究了不同施肥下土壤全磷、Olsen-P、Mehlich1-P、CaCl2-P含量及磷吸持指数(PSI)、磷饱和度(DPS)的变化,探讨不同施肥处理土壤对磷的吸附和解吸特征,并分析了土壤磷指标与土壤有机碳、pH、CEC之间的关系。结果表明:长期施用化学磷肥有利于补充土壤磷素,特别是土壤全磷,并使Olesn-P和Mehlich 1-P有增加趋势,而对CaCl2-P影响不显著;施用化肥对DPS影响不显著,单施磷会降低PSI,低量氮磷钾提高了PSI,高量氮磷钾处理与对照差异不显著;长期施用有机肥(猪粪)土壤全磷增加,而Olsen-P、Mehlich 1-P和CaCl2-P则大幅累积, PSI显著降低, DPS显著增加。长期施用化肥处理土壤对新添加磷的吸附较强,长期施用有机肥降低了土壤对新添加磷的吸附;土壤全磷、Olsen-P、Mehlich1-P、CaCl2-P、PSI、DPS及最大吸附容量(Qm)与土壤pH、CEC、土壤总有机碳(TSOC)、土壤水溶性有机碳冷水提取水溶性有机碳(CWSOC)和热水提取水溶性有机碳(HWSOC)]间相关性较高;土壤磷指标和土壤有机碳、pH、CEC指标之间存在典型相关关系,第1对和第2对典型变量的典型相关系数分别为0.997和0.951,达显著水平。研究表明,施用有机肥是调节土壤磷的供给和保持的重要措施,土壤水溶性有机碳和pH可能是反映红壤磷素供应和流失的关键指标。

Effect of long-term fertilization on soil phosphorus characteristics and loss risk of red soil

In order to determine the effects of long-term fertilization on soil phosphorus loss risk in red soil, a study on soil phosphorus adsorption and retention and the related driving factors in red soils was conducted. A long-term fertilization experiment was started in 1986 under double corn cropping system in Jingxian County, Jiangxi Province. The treatments included no-fertilizer control (CK), sole chemical nitrogen fertilizer (N), sole chemical phosphorus fertilizer (P), sole chemical potassium fertilizer (K), chemical N, P and K fertilizers (NPK₁), double doses of chemical N, P and K fertilizers (NPK₂), sole organic manure (OM), and organic manure plus chemical N, P and K fertilizers (MNPK). Soil total phosphorus (TP), available phosphorus (Olsen-P), double acid-extractable phosphorus (Mehlich 1-P), water-soluble phosphorus (CaCl₂-P), phosphate sorption index (PSI), and phosphorus saturation degree (DPS) were measured. Isothermal adsorption and desorption characteristics of soil phosphorus were determined and the relationship between soil phosphorus parameters and soil organic carbon, pH and CEC analyzed using simple and canonical correlation analyses. The results showed that long-term application of chemical phosphorus fertilizer supplemented soil phosphorus (especially TP) and increased Olsen-P and Mehlich 1-P, but had no significant effect on CaCl₂-P. The effect of chemical fertilizer application on DPS was not significant. Phosphorus fertilizer reduced PSI, NPK₁ treatment increased PSI, but NPK₂ had no significant difference with CK. Under long-term application of organic manure (pig manure, OM and MNPK), soil TP and DPS increased, then Olsen-P, Mehlich 1-P and CaCl₂-P accumulated significantly, but PSI decreased. Results from soil P sorption isotherms simulated using the Langmuir equation produced a coefficient in the range of 0.862-0.989. CK and chemical fertilizer treatments had high maximal phosphorus adsorption (Q_m) and phosphorus adsorption affinity constant (k), while under long-term organic manure application (OM and MNPK treatments) Q_m and k reduced. The isotherms for phosphorus desorption showed that CK and chemical fertilizer treatments increased phosphorus desorption rate with increasing phosphorus concentration. Organic fertilizer treatments (OM and MNPK) had high phosphorus desorption rate under low phosphorus concentration, but low phosphorus desorption rate under high phosphorus concentration. Under long-term application of chemical fertilizers, soils phosphorus adsorption and fixation increased with new additions of phosphorus, but organic fertilizers reduced phosphorus adsorption in the soil. Soil TP, Olsen-P, Mehlich 1-P, CaCl₂-P, PSI, DPS and Q_m had significant correlation with pH, CEC, soil total organic carbon (TSOC), cold water soluble organic carbon (CWSOC) and hot water soluble organic carbon (HWSOC). There was a canonical correlation between soil phosphorus indexes and soil organic carbon, pH and CEC, with significantly canonical correlation coefficients of 0.997 and 0.951 for the first and second pairs of typical variables. The correlation coefficient between water soluble organic carbon (HWSOC and CWSOC) and the first pair of typical variables (U₁ and V₁) was highest, followed by soil pH. The study showed that the application of organic fertilizer positively affected soil phosphorus supply and retention. Soil water soluble organic carbon and pH were key indexs of phosphorus supply and risk of phosphorus loss in red soils.