Abstract:In the region of black soils,spring drought does great damage to wheat,but may not give anydamage to cultivated crops such as soybean and corn.Therefore.in years of spring drought,less wheat and more soybean and corn should be plantrd.Adoption of comprehensive agricultural technique including reasonable cultivation system of reserving soil water,correctly using soil water after removing crops,selection of good varieties and rltional fertilizing system,may also give a higher yield of wheat even in years of sprint drought.But,if we want to improve the water condition in black soils perfectly,we should increase the proportion of soybean and corn in the rotation system,and give up the cropping system of wheat-wheat-soybean.In this way,we could decrease the soil water consumption in the rotation system and establish a favorable and balanced water cycle in this soil region.

Abstract: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.

Abstract:Field eaperiments for comparison of the effect of different tillage methods on the rice and wheat yield have been carried out in Wuzi county during the year of 1978-1979.The experiments showed that the fertility of the upper part of plowed layer was promoted and the soil structure was improved more remarkably due to a cropping of wheat.The traditional method of soil tillage included plowing and harrowing under waterlogged condition before rice transplanting,therefore the fertile surface soil was always turned over and soil structure was disintegrated.Pot experiments showed that mechanical disturbance of soil has no benefit to liberation of nutrients.No tillage after stubble cleaning led to the disturbance of soils to a minimum,and it was beneficial for the maintenance of soil structure and growth of rice.Deep ploughing in autumn was favorable for the growth of wheat and improvement of soil structure.Based on the results obtained it is recommended that a more rational tillage system might be no tillage in spring in combination with deep ploughing in autumn in this region.

Abstract:The present paper deals with the effect of the components of paddy soils on the specific adsorption of copper ion and it's behavior.The samples used in present experiment were collected from Southern Jiangsu province,and they were obtained from the cultivated layers of paddy soils derived from lacustrine deposits with pH 6.2-6.8.Incubated samples were also used in this experiment.The methods and results of experiment are summarized as follows:1.The amount of specific adsorbed copper is the amount of fixed Cu⁺⁺ of soil which can not be replaced by NH₄⁺ ions but may be extracted by 0.1 N HCI.The Δ value of CEC,an ezpression of the specific adsorption sites in soil,is a reducing value of CEC of soil samples saturated previously with 1 N CuC_l2 before determining the CEC by routine method.The amount of specific adsorbed Cu⁺⁺ minus the Δ value of CEC is termed the "difference value" which is an another expression of specific adsorption sites in soils.2.The value of CEC was significantly correlated with free iron oxide and amorphous iron oxide (Table 3,Fig.1).The decrease in Δ valve of CEC of samples asa results of their deferrization showed a significant positive correlation with the amount of free iron oxide removed (Table 4,Fig.2).It is indicated that the free iron oxide may play an important role in the specific adsorption site which is expressed as the Δ value of CEC.In addition,the amount of adsorbed copper approached to the Δvalue of CEC when the matter was removed by H₂O₂ (Table 5).It gives another evidence for the conclusion mentioned above.3.In free iron oxide,amorphous iron oxide is thought to exert the most important effect on specific adsorption,because it is rnore active.It was confirmed by the result obtained from incubated samples that the Δ value of CEC increased with increasing activity of iron oxide,and there were highly significant correlations between them with a correlation coefficient of 0.865** (Fig.3).4.The "difference value" showed a significant correlation with organic carbon and complex-iron contents of the incubated samples (Table 4,Fig.4),in the natural paddy soils,there were no significant correlation between them.But there was highly significant correlation between the "difference value" and the amount of organic material remained in residue of deferrized samples (Table 4,Fig.6).On the other hand,the removal of organic material led to elimination of the "difference value" from the amount of adsorbed copper approximately (Table 5).These results further indicate that the organic matter is the another form of the carrier of specific adsorption of copper expressed as "difference value".

Abstract:In this paper,the basic substances of soil fertility and their variations in black soils with various exploiting periods and various levels of fertility are discussed.The results show that:1.According to the correlation analyses,soil organic matter has significant correlations with soil N status and CEC.It means that the status and amounts of organic matter have a marked influence on the physico-chemical and bio-chemical properties of soil,and the activities of enzymes characterize the variations of the status and amount of orgenie matter to a certain degree.In black soils,the organic matter is predominant.It is considered that the core of fertility in black soil is organic matter and the activity of enzymes can be used as an important auxiliary index to characterize the level of fertility in black soils.2.After exploited,the total amount of organic matter and the amounts of humic and fulvic acids are decreased obviously with the increase of exploiting periods.The amount of active humic acid has a little increase in thick black soil or few changes in meadow black soil in initial years of exploitation,but decreases gradually after that.Humin,a more stable component of humic substances,also decreases with the increase of exploiting periods.Correspondently,the activities of all sig enzymes tested show a tendency to decrease with the increase of exploiting periods.But the activity of polyphenol oaidase in cultivated soils is markedly lower than that in virgin land.As for enzymatic activities,the activities of all enzymes (expect that of polyphenol oaidase) are weakened with the depth of both virgin land and cultivated land.3.In thick black soil,there is a remarkable difference in levels of fertility between fertilized lands and usual lands.In the former,the total amounts of organic matter and various components of humic substanses are higher,the activities of catalase and invertase are higher,and those of polyphenol osidase and phosphatase are lower than the latter.

Abstract:Chinese fir (Cunningha}mia lanceolata) is one of the most important timber conifers in our country;nevertheless,the forest cannot grow well due to the soil deterioration resulted from the successive reforestation on a same cutting area of the same species.The present paper deals with the preliminary investigation on the relationship between the nutrition status of soil and reforestation of Chinese fir The results obtained from experiments revealed that in comparison with the broad-leaved trees,Chinese fir took np much more nutrients from the soil and returned much less nutrients in the form of litter to the soil.In addition,the soil under Chinese fir plantation was liable to be eroded in the early growing stage due to the bare soil surface and intercropping of food crops,whereas under the broadleaved mixed forest almost no erosion was found and the fertility of soil tended to be promoted.

Abstract:This paper deals with the water regime of yellow-brown earths of various textures under Chinese fir (Cunninghamia lanceolata) stands and its growth.Experimental data for two years were treated with multivariate analysis methods.The curve of e}easonal variation and the results of cluster analysis of moisture regime in soils with various textures showed that in spite of existence of six texture grades of the soils used in the experiment,there were only two types of soil water regime,i.e.the type of the soil with light texture and that of the soil with heavy texture.The results of correlation analysis showed that the seasonal variation of soil moisture of the light texture type was closely related with tree growth;on the contrary,that of the heavy texture type did not present such correlation with an exception of severe drought condition.The results of multiple regression analysis has demonstrated that in soils of light texture type,one can predict the soil water regime of a month after according to the data of precipitation and evaporation on hand;but this method can not be applied to the soils of heavy texture type.Besides,marked distinction was found between the data of soil moisture regime determined in situ and these obtained from soil column in laboratory investigation by precedent authors.

Abstract:An eaperiment on the degradation of γ-BHC (r-hegachlorocyclohezane) by microbial populations was carried out using soil samples from orchards and wheat fields in which BHC applied for many years.It was found that γ-BHC in soils could be degraded more rapidly by soil microbes under the optimum temperature and adequate soil moisture conditions.All of the γ-BHC added in soil (700μg/lOg soil) were completely degraded within 56 days under favorable moisture conditions.Microorganisms being able to use γ-BHC as their sole carbon source for growth were isolated and counted on a selected medium.It was shown that both in shaking culture and sterilized soil enlture γ-BHC was degraded obviously by Flavobacterium sp.350^#,Agrobacteriumsp.70^# and Alcaligenes sp 670^#.63.1% of the γ-BHC applied were degraded by Flavobacterium sp.350^# within 84 days.It was noticed that the microbes did not transform the γ-BHC into β-BHC which is more harmful to human being either in soil culture or in pure culture.

Abstract:It is concerned significantly with the agricultural practice whether the alkalization of salt-affected soils in coastal region occures after their reclamation.The present investigations both in fields and laboratory deal with this respect of the salt-affected soils in coastal region in Jiangsu,Zhejiang and Liaoning provinces.The results are summarized as follows:1.In the process of intensive salinization resulted from the action of underground water with high mineralization rate because of the process of Ca⁺⁺ on soil absorptive complex exchanged by Na⁺,the alkalization will takes place in coastal salt-affected soil.It's alkalinity is positively correlated with salt content of the soil.Generally,the coastal salt-affected soil does not show the characteristics of alkaline soil due to the influence of a large quantity of neutral sodimn salt in soil solution.2.Under the process of soil evolution or the conditions of its reclamation and utilization,dealkalization of the soil will be taken place with the proceeding of desalinization in the soil,which means the decrease of absolute content of exchangeble Na⁺ on soil absorptive complex and the decline of alkalinity of the soil.So long as appropriate and reasonable measures of water management,agricultural and forest practice are adopted in accordance with the local conditions,the soil alkalization could be controlled.3.The phenomenon of increase of soil pH and total alkalinity in the process of desalinization of coastal salt-affected soils should be analyzed by the view point of soil genesis.This phenomenon may occur under the processe of soil desalinization and the alkalization taken place simultaneously,and it may also occur under the process of dealkalization and desalinization.In the later case,with the leaching of large amount of neutral salts,the temporary increase of pH and total alkalinity may be induced by the hydrolysis of exchangeable Na⁺ on soil absorptive complex,which just illustrated the beginning of soil dealkalization and not the occurence of alkalization.It is also proved by the data of our investigations that the alkalinity decreased with the further developing of desalinization of the soil.The dealkalization process occured simultaneously with the desalinization in coastal salt-affected soils may be related to the CaCO₃ and biological activities in the soil.

Abstract:The data used in this paper are obtained from 13 selective soil profiles and wea thered parent rocks which were collected from Taoyuan county in northern Hunan province.A discussion is made on the content of elements,profile differentiation and element loss by eluviation and accumulation of elements of main soil groups.The main soil groups in this area are roughly distinguished into four geochemical types on the basis of their difference in geochemical characteristics,namely,Relic carbonated,Weakly ferallitic,Ferallitic,and old ferallitic types.Yellow-red earth as a tonal soil is characterized by bioclimatic and geochemical properties in this region.The remarkable eluviation of base,Si,Zn and Ni,accumulation of Fe,Al,Mn,Co,Cu,and Cr,and marked differentiation of elements in profile significantly reflect the geochemical characteristics in the formation of this soil,and according to its geoehemical characteristics,this soil is regarded as the ferallitie type in soil-geoche-mieal classification.Of course,there are various soils of different geochemical types in this area on the basis of different processes of soil formation.Therefore,it is of great significance to take the geochemical characteristics into consideration for classification and amelioration of soils.

Abstract:黄河自河南郑州桃花峪以下为地上河,两岸大堤外侧形成宽约2—10公里的浸润盐渍区。黄河浸润盐渍区在黄河高水位的影响下,地下水矿化度虽然只有1克/升左右,但地下水位浅,沥涝和土壤盐渍化十分严重,治理也较困难。目前,黄河河床仍在不断淤高,本区水盐平衡状况有进一步逐渐恶化的趋势。要使本区治理收到良好的效果,就必须了解黄河浸润盐渍区的特点和掌握水盐运行规律,并采取针对性的改良方法。