Studies On The Evolution Law Of The Fertility Quality Of Arable Land And Its Influencing Factors In Red Soil Hilly Areas

Red soil hilly region in southern China is the most important agricultural production base.It is a region with a total area of the national land area of about 1 / 5.Its population accounts for 40%of the country,and the farming occupies 30%of the country.It supplied nearly half of the food needed for all population in China.So there is very important theoretical and practical significance for this arable land's quality evolution tendency and mechanism's research.According to the massive research reports and other materials(the materials of the second soil survey of Ningxiang County by myself and soil fertility of arable land survey of Ningxiang,the research and analysis of the location test for the paddy fields in Ningxiang with long-term fertilization for 18 years and the location test for the dry land of different parent materials with iong-term fertilization for 23 years in the Qiyang Red Soil Experiment Station of the Chinese Academy of Agricultural Sciences),I obtain the main conclusion that follows.1) Do the comparative research and analysis by utilizing the materials of the second soil survey of Ningxiang County in 1979 and soil fertility of arable land survey in 2002.The result shows that in the past 20 years,the organic matter and nitrogen content in paddy fields of Ningxiang County has been obviously increasing.The effective phosphorus content in soil doubled.Potassium element showed a trend of loss.The research also indicated that changes in the fertility of dry land have the same trend with the paddy fields,but the fluctuation scope is different.Particularly in the rice fields,the soil acidification became so serious.This findings also indicated that under the current fertilization level,the main factor of restricting rice's outputs doesn't rely on soil nutrients but the profile pattern,the obstacles horizon,parts of the terrain and soil parent material and such other descriptive factors,so the experts' suggestion is that reduce the nitrogen and phosphate fertilizer and increase the potassium fertilizer or back grass fields;The findings also indicated that the evolution of soil fertility influenced by the environmental condition and the inherent nature of soil appears the spatial variation,so these factors should be considered when we make the plan of fertilization.2) Through different long-term tests located in Ningxiang County of Hunan province,the researchers study the impact of different fertilization on the soil quality of paddy field.The findings showed that the fertilization is an important safeguard for high yield.The output of early rice with irrigation is higher up to 107%—127%than that of non-irrigation,meanwhile for late rice with irrigation it is higher up to 70%-84%than that of non-irrigation.During the whole fertilization process,the output which contained the organic fertilizer with nitrogen is the highest, accounting for 30%of the total nitrogen(i.e.the OM30 processing).There is a significant improvement on the soil organic matter,total nitrogen,alkali-hydrolysable nitrogen and the effective phosphorus,which are fertilized by OM30 processing.And the Straw Back Yield can bring the benefit for the increase of soil total K and available K.Therefore,the local farmer can take the OM30 fertilizer procession and carry the Straw Back Yield,in order to balance soil nutrients to enhance the output and quality,and increase the utilization rate of fertilizer to ensure the sustained stable yield and high quality.3) Through the long-term location test for the dry land of different parent materials laid by Qiyang Red Soil Experiment Station of the Chinese Academy of Agricultural Sciences,the research applies on the impact of different fertilization on different parent material.The research indicated that the soil with higher fertility and good nutrient preserving and supplying capability, will get the relatively less impact on crop output from fertilization,on the contrary it will get more. Fertilization is good for the plant growth by increasing the content of organic matter,total nitrogen and alkali-hydrolysable nitrogen,which contain in the soil of dry land.Stalk return to field also can improve the soil quality,especially help to improve soil nutrient K.4) Through investigating the crop output of dry land and paddy fields in Ningxiang County and survey visiting,observing,sampling and determination the soil and environmental factors of the paddy field and the dry land,such as the topography,soil parent material,the underground water level,the irrigation and flood drainage,topsoil and soil thickness,soil texture,soil pH,bulk density,barrier layer and so on,the researchers use the degree of association between crop output and the soil and the environmental conditions to determine the analysis of the size of soil and environmental conditions' affect on the soil quality.There is no report of this method at home and abroad.The result indicated that suitable thickness of paddy soil is about 15cm,and for dry arable land it should not be lower than 20cm;The alluvial rivers parent material is the best one to influent the output,the rice fields is the worst with the parent material of slate ground,while the dry and plough land is the worst for its purple sand shale parent material;The paddy rice is best with the acid soil,and the dry crop is the best with the neutral soil;The obstacles horizon exist in 35.2%of the rice fields in research region,and many for middle or top digit obstacles.It is also the main factor which influent the whole output increase of rice;Paddy rice and drought-enduring plant take loam soil as best,among of them,the sand is bad for rice raisings,while stick sand harm to drought-enduring plants;The bulk density of paddy rice is suitable for 1.00-1.29g/cm~3; Compared to drought-enduring plants,paddy rice needs thicker soil layer.The effective thickness of the layer for rice land should not be less than 65 centimeters,and for dry it should not be less than 50 centimeters.The research also showed that the altitude is higher,and the output is lower; The terrain affects the output through hydrological conditions,for example,higher terrain will get lower production in these places such as the upper slopes and fields with high bank or low-lying paddy fields,and low-lying land between the mound;However,the paddy fields placed in the middle of terrain,such as the high floodplain and the first and second terrace,will get higher production.This may be due to topographic impact on the irrigation & drainage and also the soil material cycle.The output of diy arable land and topographical height are anti-related for each other.It means that the output in mountainous area is higher than that of hilly and gang land,while the latter's production is lower than that in the terrace.The deeper water table is beneficial to the rice's production.In fact,we should aim at descending the water level to 50 centimeters below when digging the drainage channel.Regarding the arable land,the high guaranteed rate for irrigation is the powerful safeguard for the high yield,and also it is better with a strong capacity of drainage.Ensuring high-yield rice based on cooperating the irrigation and drainage together,and making sure that both of them can be scheduled in a timely manner.5) Utilizing the materials of the second soil survey of Ningxiang County and soil fertility,as well as the findings of long-term location tests of fertilization on the paddy fields of Ningxiang and dry land of Qiyang,the researchers proposed the major land conservation techniques in summary and induction.The technologies of the conservation for paddy fields are following: First,dealing with inorganic-based fertilizer,and combining the organic one.Second,we should focus on the idyllic construction of farmland.Also we should take the system of irritation to the core,and put construction mainly on pushing the high & filling the low land,lowering the groundwater level of depression field and cultivating the appropriate thickness of topsoil.That is the basis of reaching a high and stable field.Third,promoting to return stalk and straw to field, and make full use of the K resources of stalk and straw.Fourth,the paddy fields whose PH lower than 5.5 should be applied for the alkaline fertilizer in proper way such as lime,fused calcium and magnesium phosphate and steel slag with phosphate fertilizer.That will reduce soil acidity.Finally, the parent material is an important reference for fertilization.The technologies of the conservation for dry land are following:First,the important measure to rich the fertility of dry land and increase the output is to take the organic manure mainly and also combing the inorganic fertilizer.Second, cultivating the fertile and deep plow layer is great important to the producing of dry crops.The thickness of plow layer in dry land should be bigger than 20 centimeters.Third,the soil pH less than 5.0 should employ alkaline matters such as lime and so on.From this,the soil pH will get higher and it will help to raise the output.