Status Of Paddy Soil Nutrients And Soil Limiting Factors In Hunan Province

1.The mean values of pH,organic matter,cation exchange capacity,total nitrogen,alkali-hydrolyzable nitrogen,available phosphorus,total potassium,available potassium,exchangeable calcium and exchangeable magnesium in paddy fields in Hunan province were6.15,26.19,10.6 cmol/kg,1.15,140.39,14.13,11.27,60.06,532.54,144.48 mg/kg,respectively.The distribution ranges were 4.85～7.85,8.03～76.96 g/kg,1.13～44.72 cmol/kg,0.28～4.06 g/kg,41.46～345.36 mg/kg,0.68～106.76,4～17.5 g/kg,19.95～199.77 mg/kg,67.27～4967.64 mg/kg,19.44～508.37 mg/kg.In terms of the distribution of different rice areas,the pH value was high in the north and south of Hunan,and low in the middle and east of Hunan and west Hunan.The organic matter is high in southern and western Hunan,and low in central and eastern Hunan and northern Hunan.There was no significant difference in cation exchange capacity among rice regions.The total nitrogen was high in the north and south of Hunan,and low in the west and east of Hunan.Alkali-hydrolyzable nitrogen was higher in central and eastern Hunan and southern Hunan,and lower in northern and western Hunan.The available P was high in western Hunan,and low in eastern,northern and southern Hunan.The total potassium was high in western and northern Hunan,and low in central and southern Hunan.The available potassium was high in the south,north,middle and east of Hunan and low in the west.The exchangeable calcium was high in southern Hunan and low in eastern,northern and western Hunan.The exchangeable magnesium is high in northern Hunan,low in central and eastern Hunan,south Hunan and west Hunan.2.In terms of the comprehensive fertility of paddy fields,the north of Hunan was the highest,the south of Hunan,the middle and east of Hunan followed,and the west of Hunan was the lowest.The soil comprehensive fertility of Changde,Xiangtan and Yueyang was the highest,and that of Xiangxi Autonomous Prefecture was the lowest.3.(1)The pH of paddy field was significantly positively correlated with cation exchange capacity,exchangeable Ca and exchangeable Mg,significantly positively correlated with available K,significantly negatively correlated with available P,and significantly negatively correlated with total K.According to the comprehensive analysis,most of the nutrients in the paddy field were suitable for rice growth when the pH was in the range of 5.63～6.06.(2)Organic matter was significantly positively correlated with total nitrogen,alkalohydrolyzable nitrogen,cation exchange capacity and exchangeable calcium.In summary,the organic matter at 20-35 g/kg was more suitable for the growth of rice.(3)The cationic exchange capacity was significantly positively correlated with pH,alkalohydrolyzable nitrogen,available potassium,organic exchangeable calcium,exchangeable magnesium,and total nitrogen.In conclusion,when the cationic exchange capacity was between 22.1 and 24.7 cmol/kg,most of the nutrients were suitable for rice growth.