氮磷提高华北落叶松人工林地土壤养分和酶活性的作用

【目的】采用田间试验,研究外源施用氮、磷肥对处于中龄林的20年华北落叶松(Larix principis-rupprechtii)人工林地土壤养分和酶活性特征的影响,并对土壤肥力水平进行评价,以筛选出最佳施肥方案。【方法】2012年4月中旬对处于中龄林的20年华北落叶松人工纯林进行外源施用氮、磷肥,在5月到10月中旬采集0—20 cm土壤样品,测定土壤养分和土壤酶含量,分析其在整个生长期内的动态变化,运用主成分分析法筛选出最佳施肥方案。【结果】1)施用氮、磷肥显著增加土壤速效氮和速效磷含量(P0.05),降低土壤速效钾含量和p H值。与对照相比,不同施肥处理速效氮增加幅度为N2PN2N1PN1P,速效磷为N1PPN2PN2N1,而速效钾降低幅度为N2PN1PN2PN1,p H降低幅度为N2PN2PN1PN1。2)施肥后,土壤蔗糖酶、磷酸酶和脲酶活性显著增加(P0.05),过氧化氢酶活性降低。与对照相比,不同施肥处理蔗糖酶增加幅度是N1PN2PN1PN2,磷酸酶是N2PN1N1PN2P,脲酶是N2PN1PN1N2P,而过氧化氢酶降低幅度是N2PN2N1PPN1。3)土壤中养分含量对季节变化的响应非常敏感,速效氮、速效磷和速效钾整体呈先降低后增加的趋势,最小值出现在植物生长旺盛的7、8月份。土壤酶活性变化比较复杂,多数最大值出现在7、8月份。4)施氮肥、磷肥和氮磷配施处理均提高了土壤速效氮和速效磷含量,速效氮由21.56 mg/kg上升到35.77 mg/kg,速效磷由1.86 mg/kg上升到3.73 mg/kg,尤以N1P和N2P配施效果最明显。5)氮肥、磷肥和氮磷配施处理,土壤蔗糖酶、脲酶和磷酸酶活性均增加,虽然过氧化氢酶活性小幅下降,但总的来说土壤酶活性增强,以N1P和N2P配施效果最为明显。6)主成分分析表明,施肥提高了土壤肥力水平,提高效果表现为N1PN2PPN1N2CK。N1P处理土壤肥力水平增加了1.505,N2P增加了1.405。【结论】施氮、磷肥可显著增加林地土壤养分,增强土壤酶活性,有效改善华北落叶松人工林地土壤肥力状况,缓解氮、磷亏缺导致的林地地力衰退。供试条件下华北落叶松的最佳施肥方案是N 75 kg/hm2和P2O575 kg/hm2(N1P),而N 150 kg/hm2和P2O575 kg/hm2(N2P)次之。

Increase of soil nutrients and enzymatic activity by adding nitrogen and phosphorus to Larix principis-rupprechtii plantation

【Objective】 A field experiment was conducted to study effects of exogenous nitrogen and phosphorus fertilization on soil nutrients and enzyme activities, and select proper fertilizer amounts for the half-mature Larix principis-rupprechtii plantation in the Qinling Mountains of China. 【Methods】 Nitrogen and phosphate fertilizers were applied individually or together in three levels in a 20-year-old half-mature Larix principis-rupprechtii plantation in mid April 2012. Soil samples in 0-20 cm depth were collected from May to October 2012, and the soil nutrient contents and enzyme activities were measured. The principal components analysis was used to select the optimum fertilization scheme. 【Results】 1) The application of nitrogen and phosphorus fertilization significantly increases the soil available nitrogen(N) and available phosphorus(P) contents, but decreases soil available potassium(K) content and pH. The increase levels of different treatments in soil available N was in the order of N2PN2N1PN1P, and available P in N1PPN2PN2N1, while the soil available K decrease was in the order of N2PN1PN2PN1 and pH in order of N2PN2PN1PN1. 2) The activities of soil invertase, phosphatase, and urease could be significantly increased, but that of hydrogen peroxidase decreased by the N and P fertilization. The increase levels of the soil enzyme activities for invertase are in the order of N1PN2PN1PN2, for phosphatase are N2PN1N1PN2P, and for urease are N2PN1PN1N2P, while the decreased of hydrogen peroxidase are in the order of N2PN2N1PPN1. 3) The responses of soil nutrient contents are sensitive to seasons. The available N, P and K contents decrease firstly and then increase during the year, with the minimum values appeared in plants in July and August. The changes of soil enzyme activities are complex, most often the maximum values are also appeared in July and August. 4) Nitrogen and phosphorus fertilizer alone, or their combined application could increase the contents of soil available N and available P. The soil available N is increased from 21.56 mg/kg to 35.77 mg/kg and soil available P from 1.86 mg/kg to 3.73 mg/kg. The soil fertility levels are improved by fertilization, with satisfactory effects with the N1P and N2P treatments. 5) Both the nitrogen and phosphorus fertilization could increase the activities of soil invertase, urease and phosphatase, but decrease hydrogen peroxidase activity slightly. The fertilization generally increases the soil enzyme activities. 6) The principal components analysis indicates that the fertilization could significantly improve soil fertility levels with the order of N1P N2P P N1 N2CK. The highest increase is 1.505 in N1P, then is 1.405 in N2P.【Conclusions】 Fertilization is capable of enhancing soil nutrients and enzyme activities, thus improving soil fertility and alleviating the decline in soil fertility caused by nitrogen and phosphorus deficiencies in the Larix principis-rupprechtii plantation. The proper fertilization amount is N 75 kg/hm2 and P2O575 kg/hm2 (N1P), followed by N 150 kg/hm2 and P2O575 kg/hm2 (N2P)