(土娄)土旱地土壤硝态氮季节性变化与夏季休闲的培肥增产作用

黄土高原广大产麦地区在夏作物如小麦、豌豆、扁豆等收获后,进行夏季休闲,伏耕晒垡,以保证其后作小麦丰产稳产。此项耕作措施是农民在长期生产实践中创造出来的一种保持土壤肥力的宝贵经验。二千多年前,氾勝之^[1]在关中地区教导农业时曾对这些宝贵经验进行过总结。新中国成立后,一些农业科技工作者^[2-17]就此经验曾在陕西、甘肃、宁夏、内蒙、山西等地进行试验研究与调查总结。有些地区或者因为夏粮欠收,大搞以秋补夏,夏作物收后复种秋作物;或者为了多生产粮食,盲目扩大复种指数。二者均挤掉了夏季休闲。各地农业生产领导部门和农业科技工作者对此意见分歧,并进行广泛讨论。本文从缕土早地土壤中硝态氮季节性变化出发,阐明夏季休闲的培肥增产作用以及提高夏季休闲效果的途径。可供黄土高原主要是璞土早作地区进行耕作改制时参考。

THE SEASONAL VARIATION OF SOIL NO3-N AND THE EFFECT OF SUMMER FALLOW ON THE FERTILITY OF MANURED LOESSIAL SOIL

Manured loessial soil (Lou soil) is one of the mam cultivated soils in the loess region of Shaanzi and Shanzi provinces of Northwestern China.This paper deals with the seasonal variation of soil NO₃-N and the effect of summer fallow on the fertility of "Lou" soil.Field survey,field experiments and periodical tests of permanent plots were carried out,the results obtained are as follows:1.In the cropping system of summer fallow-winter wheat,the seasonal regime of soil NO₃-N might be divided into five periods annually,i.e.,the periods of accumulation,leaching,equilibrium of supply and requirement,supply-requirement discrepancy,and that of sharp discrepancy of supply-requirement of nitrogen.2.Soil NO₂-N accumulated about 1.18-3.30 kg per mu after fallow,and leaching depth of soil NO₃-N ranged from 1-2 m below topsoil.The regression equation of leaching depth of NO₃-N (Y mm.) and rainfall (X mm.) during the period of summer fallow was Y=3.86 X.3.Soil NO₃-N accumulated after summer fallow could meet the need of nitrogen for the early growing stage of wheat.Thus the accumulated nitrogen provided a foundation for high yield of crop.Yield of winter wheat after summer fallow was 57.5-124.0% (average 85.3 %)higher than the yield of winter wheat after autumn crop.4.In order to promote the favorable effect of summer fallow on soil fertility,attention should be paid on the time,depth and quality of summer ploughing.In addition,it is necessary to apply adequate organic manure or plant quickly growing green manure crops.5.Under the condition of dry farming,if the rainfall is less than 300mm in the summer fallow period and the amount of manure is less than 2500 kg per mu,rotation system of wheat and summer fallow is appropriate;if the rainfall is sufficient (more than 400 mm) and the amount of manure is also sufficient (5000-7500 kg per mu),the cropping indea may be increased relatively.