漫灌和滴灌棉花土壤有效磷丰缺指标与临界值研究

Abundance index and critical level of phosphorus in cotton soils under flooding and drip irrigation

【目的】土壤有效磷含量是棉花施用磷肥的重要依据,由于连续多年施用磷肥,新疆棉花土壤有效磷含量有较大幅度的增加,但对棉花土壤有效磷的评价仍然使用以前的标准,磷肥推荐用量不能适应棉花生产。因此,明确土壤有效磷的临界值,能为有效指导棉花合理施用磷肥提供理论依据。【方法】选择新疆281个试验点,建立缺磷区相对产量与土壤有效磷含量之间的关系,进行对数方程模拟,分别将相对产量带入相应的对数方程,求出对应的土壤有效磷分级指标值,同时采用线性+平台模型拟合求出土壤有效磷临界值,根据有效磷分级推荐施用磷肥。【结果】对棉花产量和土壤有效磷的相关性进行直线、指数和对数模拟,3种回归方程的相关系数都达到了1%显著水平,其决定系数R^2分别为0.500、0.470和0.590,以对数回归方程相关性最高。采用线性+平台模型拟合棉花相对籽棉产量和土壤有效磷的关系,棉花相对籽棉产量对土壤有效磷含量的反应分成2段,拐点即为土壤有效磷临界值,此时棉花土壤有效磷的临界值为22.0 mg/kg。当土壤有效磷≥22.0mg/kg时,y=93.77,表明随土壤有效磷的增加,棉花相对籽棉产量不变,此时施用磷肥几乎没有增产作用;当土壤有效磷<22.0 mg/kg时,y=62.86+1.405x,施磷肥可以促进棉花增产(R^2=0.63**)。棉花的磷肥利用率随土壤有效磷含量的增加而大幅度降低。当土壤有效磷<5 mg/kg时,漫灌条件下磷肥的利用率为25.7%,滴灌为21.6%,二者差异不显著;当土壤有效磷5~12 mg/kg时,漫灌和滴灌条件下磷肥的利用率也没有显著差异;当土壤有效磷12~25 mg/kg时,滴灌条件下磷肥的利用率为15.0%,比漫灌显著增加4.6个百分点;当土壤有效磷为25~38 mg/kg和>38 mg/kg时,漫灌和滴灌条件下磷肥的利用率差异又变得不显著。不论漫灌和滴灌,棉花磷肥的平均利用率约为15.9%。【结论】根据棉花相对产量的<70%、70%~80%、80%~90%、90%~95%、>95%,将土壤有效磷划分为5个等级,即<5 mg/kg、5~12 mg/kg、12~25 mg/kg、25~38mg/kg和>38 mg/kg,土壤有效磷临界值为22.0 mg/kg。漫灌条件下磷肥的平均利用率为15.2%,而滴灌条件下磷肥的平均利用率为17.1%,差异不显著。棉花土壤有效磷丰缺指标为极低、低、中、高、极高,获得了土壤有效磷临界值及不同棉花产量下的推荐施磷量。

[Objectives]Content of Olsen-P in soil is an important basis for phosphate fertilizer application on cotton. Olsen-P in cotton soils in Xinjiang has increased greatly because of the application of phosphate fertilizers for many years. The old standard was used to evaluate the Olsen-P status in cotton soils, and the recommended rates of P fertilizer could not adapt to cotton production. Therefore, the critical level of soil Olsen-P was determined to provide theoretical basis for managing phosphate fertilizers on cotton.[Methods]Relationship between the relative yield and soil Olsen-P was established basing on 281 test sites in Xinjiang, and a logarithmic equation model was obtained. The relative yield was taken into the corresponding logarithmic equation, and the corresponding soil Olsen-P classification indexes value were obtained. At the same time, the critical level of soil Olsen-P was calculated by linear ＋ platform model fitting. Phosphate fertilizer was recommended according to the Olsen-P deficiency index.[Results]The correlation between cotton yields and soil Olsen-P contents was regressed with linear, exponential and logarithmic models. All the correlation coefficients of the 3 regression equations reached 1% significant level, with the R2 of 0.500, 0.470 and 0.590, respectively. The logarithmic regression equation gave the highest correlation. The relationship between relative cotton yield and soil Olsen-P content was fitted by linear ＋ platform model. The response of relative seed cotton yield to soil Olsen-P content was divided into two stages. The inflection point was the critical level of soil Olsen-P, and the threshold of soil Olsen-P was 22.0 mg/kg. When soil Olsen-P ≥ 22.0 mg/kg, y=93.77, showed that relative yield of cotton was constant with the increase of soil Olsen-P, and application of phosphate fertilizer almost did not increase the yield. When the soil Olsen-P 〈 22.0 mg/kg, y=62.86 ＋ 1.405x, phosphorus fertilizer could promote cotton yield （R^2=0.63＊＊）. The phosphorus utilization rate of cotton decreased with the increase of soil Olsen-P. When the soil Olsen-P 〈 5 mg/kg, phosphate fertilizer utilization rates had no significant difference between flood and drip irrigation, which were 25.7% and 21.6%, respectively. When the soil Olsen-P was 5-12 mg/kg, the phosphate fertilizer utilization rates of flood and drip irrigation were not significantly different. When the soil Olsen-P was 12-25 mg/kg, the phosphorus utilization rate of drip irrigation was 15.0%, which significantly increased by 4.6 percentage points compared with that of flood irrigation. When the soil Olsen-P was 25-38 mg/kg and 〉 38 mg/kg, phosphate fertilizer utilization rates were not significantly different between flood and drip irrigation. Average utilization rate of phosphate fertilizer was about 15.9% under flood and drip irrigation.[Conclusions]The Olsen-P contents in cotton soils could be divided into 5 grades：extremely low, low, medium, high and extremely high, corresponding to the relative cotton yield of 〈 70%, 70%-80%, 80%-90%, 90%-95%, 〉 95%. The critical level of Olsen-P in soil is 22.0 mg/kg. The average phosphorous utilization rate is 15.2% under flooding condition, and 17.1% under drip irrigation.