| Soil moisture and nitrogen utilization is the main influence factors of affecting crop growth and development.Except for the fertilization and irrigation,soil properties is the main limiting factor of crop water and fertilization utilization.Under the same conditions of climate,biology,topography,mother quality and human factors,cultivation time is the main factors which affecting the soil property.There will be some differences with thedifferent water tillage years on the paddy soil,which will lead to the moisture movement and the water and fertilizer absorption on crops.Jianghan plain is an important agricultural production base in China,the seasonalwater shortage and the low utilization of nitrogen on crops is the main influence factors to restrict the agriculture production in Jianghan Plain.Paddy field and dry land are the main land use modes in Jianghan Plain,during the development the mechanization level and economic benefit on rice,there have a new trend that the area of paddy fields has continues to increase.On the one hand,the fertilizer and irrigation water amount continues increasing with the areas increasing,and the seasonal drought and fertilizer loss compounding the problem about water pollution.On the other hand,the farm have not considered the different years of rice cultivate,it can lead to the water and fertilizer utilization further decline and the environment pollution aggravation,especially the water environment.Hence,we aimed at the different years cultivate paddy fields to carry out the soil properties and water-nitrogen research,we hope this research can help us to make the reasonable paddy management measures,to enhance the water and nitrogen utilization.And it has significances in the agriculture production and water environment protect.In this research,we select the different years water tillage of paddy fields(2 years,18years and>100 years),by field observation and lab analysis and combining the theoretical analysis.We emphasis the difference to the soil basic physic and chemical properties and hydraulic characteristics,focus the soil water and nitrogen distribution in the soil profile.As a result,we preliminary reveled the influencing mechanism that cultivation years how to affect the soil properties and water-nitrogen distribution in soil profile.Based on this,we came up with the optimizing fertilizer and irrigation measure on the different cultivation years on paddy fields.The main results of this study are as follows:(1)The basic physical and chemical properties of paddy soil has significantly different under different water tillage years.The thickness of farmland ploughing and plough layer has increased with the extension of the cultivation years.Soil organic matter was enriched in the plowing layer and increased with the extension of the age of cultivation.The average content of soil organic matter in farmland in 2,18 and 100 years was 10.97 g/kg,15.44 g/kg and 17.97 g/kg respectively.In the2 years,18 years and 100 years,farmland soil density changes ranged from 1.18-1.37 g/cm3,1.09-1.46 g/cm3 and 0.98～1.54 cm3 respectively.The bulk density of the ploughing layer is minimum,and then is subsoil layer,plow pan is the maximum.(2)Under the conditions of different years water tillage,the saturated water conductivity(Ks)has significance difference.The Ks of plough layer increases with the extension of cultivation,plow pan and subsoil layer reduce by the different water tillage years.The Ks at the subsoil layer of the plough layer decreased from 37.02 cm/d of farmland in 2 years to 3.11cm/d in 100 years.The soil water binding capacity under the depth of plowing is enhanced with the extension of the water tillage.Basic soil physical and chemical properties is the main factors influence the soil water leakage and binding capacity properties.And clay content and soil bulk density of saturated hydraulic conductivity has significant negative correlation relationship,macro pore content and saturated hydraulic conductivity has significant positive correlation.(3)Under the follow period,the soil water and nitrogen distribution has significance difference in the three farmland.Soil water and nitrate content were increased with the extension of water tillage years,with the 2 years,18 years and 100 rice paddy fields of 0-100 cm vertical section,average soil water content were 0.39 cm3/cm3,and 0.46 cm3/cm3,and 0.54 cm3/cm3 respectively,nitrate nitrogen content were 3.75 mg/kg,6.27 mg/kg and 9.85 mg/kg.The ammonium nitrogen content is has significance smaller than nitrate nitrogen,water tillage 2 years,18 years and 100 years paddy fields of ammonium nitrogen and nitrate nitrogen ratio was 0.61,0.39 and 0.30,respectively.(4)The distribution and accumulation of nitrogen in soil profile with different water tillage years paddy fields were has significantly different during wheat growing period.The soil nitrogen was enrichment in the plough layer,2 years,18 years and 100 years paddy fields soil nitrate nitrogen content in plough layer were 12.26 mg/kg,12.74 mg/kg and 14.88 mg/kg,respectively.The ammonium nitrogen were 6.01 mg/kg,8.33 mg/kg and 11.69 mg/kg,respectively.The nitrogen content was continues reduce with the depth increasing.The utilization of nitrogen in wheat was 10.03 kg/kg,6.39 kg/kg and 4.15 kg/kg respectively,which was shown to be reduced with the extension of the water tillage year and the main influencing factors of soil moisture.(5)During the rice growth of period,the distribution of water and nitrogen in soil profile of paddy fields with different water tillage years has significance difference.Soil moisture content increased with the extension of cultivated year with the water tillage.Thewater content of>100 years paddy fields(0.43 cm3/cm3),1.14 times and 1.36 times than 18 years and 2 years paddy fields,there has small difference under the plough layer.In the soil solution,nitrogen concentration has significance difference with different water tillage years,the ammonium nitrogen concentration was lower than nitrate nitrogen.The avertage soil nitrate concentrations was 0.76 mg/L,0.95 mg/L and 1.08 mg/L in 2 years,18 years and>100 years paddy field respectively.Ammonium nitrogen average convertation was3.99 mg/L and 12.61 mg/L and 12.08 mg/L,respectively.The influence factors of difference nitrate and nitrogen concentration in different paddy fields was the difference soil properties,because it lead to the different water leakage and matain characterizes,and then lead to the different nitrogen distribution in the soil profiels.(6)For the shorter years of water tillage paddy fields,we need to take the action to reduce the water and nitrogen leakeage,we can use two ways to solve this problem,on the one hand,we can increase the number of plows times to improve the plow pan’s development.On the other hand,we should reduce the irrigation amount and increase the times of irrigation.For the longer years of water tillage paddy fileds,the water and nitrogen can easily prevent by the plow pan,so we can proper reduce the times of irrigation and fertilizer,and increase the amount of water and fertilizer to reduce the labour cost,but it also needs to prevent the nitrogen wastrage by the runoff with heavy rainfalls and overring irrigation. |
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