休耕对陇中旱农区农田土壤养分的影响

Effects of Fallow on Soil Nutrients in the Dryland Farming Area of Central Gansu

[目的]评估休耕对农田土壤养分的影响,阐明休耕模式的适宜性,为区域制定合理的土地管理措施和提高农田土壤质量提供科学依据。[方法]以陇中旱农区农田为研究对象,基于2017—2019年连续3 a的休耕试验数据,选择土壤有机质(SOM)、全氮(TN)、有效磷(AP)、速效钾(AK)、pH值和交换性钙、镁7个土壤养分指标,对比绿肥种植休耕模式实施前后土壤养分的变化情况以及休耕与非休耕对照(马铃薯—玉米—马铃薯轮作)土壤养分的差异。[结果](1)与休耕前的基础养分相比,休耕3 a后,SOM,TN和AK含量均有增加趋势,增幅依次为19.5%,23.0%,9.2%,其中除AK外,SOM和TN含量休耕前后均有显著差异(p<0.05);AP,pH值和交换性钙、镁均显著降低(p<0.05),降幅依次为21.8%,1.0%,36.5%,39.6%。(2)与非休耕对照相比,SOM,TN和AK含量分别明显高于对照区3.5%,11.0%,8.5%,AP和交换性钙含量均比对照区低,其中仅TN和交换性钙的含量有显著差异(p<0.05)。(3)AP变化率与其基础含量呈显著对数关系(p<0.001),SOM,TN,AK,pH值等指标变化率与其基础含量之间均呈显著的负相关线性函数关系(p<0.01),即随着土壤基础养分的增加休耕对其养分变化的影响降低,而交换性钙镁的这种关系不显著。(4)休耕3 a后SOM,TN,AK和AP之间均呈显著正相关关系(r>0.38,p<0.05);pH值除与交换性镁的相关性不显著,与其他土壤养分指标均呈显著负相关关系(p<0.01),且休耕区上述土壤养分指标的相关性均比对照区高。[结论]采用种植绿肥的休耕模式,可使陇中旱农区耕地质量得到一定程度的提升,并且对基础养分较低的土壤效果更佳。但3 a的休耕相较于马铃薯—玉米—马铃薯轮作种植地力提升幅度较小,表明在较短的时间尺度内休耕对土壤的改良作用仍十分有限。

[Objective]The aims of this study are to evaluate the effects of fallow on soil nutrients in farmland,clarify the suitability of fallow patterns,and provide a scientific basis for developing appropriate land management measures and improving the quality of soils in this area.[Methods]Based on the fallow trial data of three consecutive years from 2017 to 2019,seven soil nutrient indexes,including soil organic matter(SOM),total nitrogen(TN),available phosphorus(AP),available potassium(AK),pH value,exchangeable calcium and exchangeable magnesium,were selected to compare the changes in soil nutrients before and after the implementation of the fallow mode of green manure cultivation and the differences in soil nutrients between fallow and non-fallow controls(potato-corn-potato rotation)by using farmland in the dryland farming area of central Gansu as the research object.[Results](1)Compared with the basic nutrients before fallow,the contents of SOM,TN and AK showed the increasing trend after three years of fallow,increasing by 19.5%,23.0%and 9.2%,respectively,in which there were significant differences(p<0.05)in the contents of SOM and TN before and after fallow,except for AK;AP,pH value,and exchangeable calcium and magnesium significantly decreased by 21.8%,1.0%,36.5%and 39.6%,respectively(p<0.05).(2)Compared with the non-fallow control,the contents of SOM,TN and AK were 3.5%,11.0%and 8.5%higher than those in the control area,respectively.AP and exchangeable calcium were lower than those in the control area.However,there were significant differences only in the contents of TN and exchangeable calcium(p<0.05).(3)There was a significant logarithmic relationship between the rate of change of AP and its basic content(p<0.001),and a significant negative linear function between the rate of change of SOM,TN,AK and pH value and their basic content(p<0.01).In other words,the effect of fallow on change of soil nutrients decreased with the increase of its basic nutrients,but this relationship was not significant for exchangeable calcium and exchangeable magnesium.(4)After three years of fallowing,there were remarkable positive correlations among SOM,TN,AK and AP(r>0.38,p<0.05).The pH value was significantly negatively correlated with other soil nutrient indexes except exchangeable magnesium(p<0.01).The correlation of soil nutrient indexes in the fallow area was higher than that in the control area.[Conclusion]The fallow mode of green manure planting can improve the quality of cultivated land in the dryland farming area of central Gansu to some extent,and it is more effective for soils with low basic nutrients.However,the three-year fallow is less effective than the potato-maize crop-potato rotations,indicating that the improvement effect of fallow on soil is still limited in a relatively short time scale.