Study On Characteristic Of Nutrients Loss From Tobacco Field In Rainy Southern

This paper took the Jianghua tobacco field of Hunan province as the investigative object in 2005²007, determined the rainfall, runoff, nutrients content of runoff, nutrients content and water content of soil profile, length and width of flue cured tobacco leaves, nutrients concentration in tobacco plant. According to these data the effect of the rainfall intensity, water content of soil before rain, and leaves area index of flue-cured tobacco on runoff, runoff coefficient were studied, the effect of nutrients content of soil profile, on nutrients content of runoff was also studied; the effect of nutrients content of soil, water content before rain, rainfall and rainfall intensity on the nutrients loss from tobacco field were analyzed; and the nutrient balance in tobacco field was reckoned out. The main results were showed as follows:1. Runoff coefficient of tobacco field (RCTF) was affected by rainfall, time distribution of rain, rainfall intensity and 0-30cm soil water content (SWT30) before rain. RCTF become larger as rainfall increased or rain event was dense. The relation between rainfall intensity ( x ) and RCTF ( y ) could be described by y = 0. 1602ln(x)+0.3516(r=0. 0.4920**), higher SWT₃₀ before rain, larger RCTF, the relation between SWT30 before rain( x ) and RCTF( y ) could be described by y = 0.0013e0.1676x(r =0.7596**), the relation between rainfall( x ) and runoff ( y )could be described by y = 0 .6639x-2.5731(r=0.9021**). We could estimate that 3.9mm was the minimum rainfall that runoff occur. The soil water content in 30-60cm and leaves area index of flue-cured tobacco (LAIFT) had no obvious effect on RCTF. The RCTF in 2005, 2006 and 2007 was 0.39, 0.64, 0.49 relatively, The average RCTF was 0.498 in three years.2. STW30 was higher than STW60, having an average increase of 7.7%.Both of STW30 and STW60 increased after rain, The former has an average increase of 4.1%, and the later has an average increase of 1.7%.3. In growth of tobacco, nitrate nitrogen content in 0-30cm soil was higher than that in 30-60cm With the growth of tobacco, nitrate nitrogen content gradually decreased, the decrease amplitude of that in 0-30cm was larger than that in 30-60cm Nitrate nitrogen content in 0-30cm soil had close relation to that in 30-60cm soil which could be described by y = 9 .0844Ln(x)?13.93(r=0.8045**).4. In growth, ammonium nitrogen content in 30-60cm soil was higher than that in 0-30cm ammonium nitrogen content in 0-30cm had larger fluctuation; the evaluation of soil ammonium nitrogen content in two layers varied among years.5. Nutrients content increased less or more after fertilization. Nutrient content in soil decreased after rain except for the content of potassium in the latter phase of tobacco growth, there was significant statistics regression relationship between nitrate nitrogen and LAIFT, the regression equations were separately y = 7 .9541x^-0.2985 (r=0.5196**)and y = 17 .368x^-0.6119(r=0.5196**).6. Nutrients loss from tobacco field and runoff took place at the same time. Numerous nitrate nitrogen loss from tobacco field happened in early growth of tobacco. The average ratio of nitrate nitrogen loss before May to that of total nitrate loss was 72.8%.7. The loss of ammonium nitrogen, rapidly available phosphorus and rapidly available potassium from tobacco field may occur in any stage of tobacco growth. Especially, the risks of nutrient loss become higher in the rainfall after tobacco field applied top-dressing and The loss of rapidly available potassium in tobacco field soil was the most companied with the loss of rapidly available nitrogen and rapidly available phosphorus, The loss in every seasonal tobacco year's average was 50.34 kg/hm², the average of loss of available nitrogen was 33.91 kg/hm², the average loss of rapidly available phosphorus was 3.41 kg/hm². The average loss of rapidly available potassium was 50.34 kg/hm². The ratio of the loss of available nitrogen, rapidly available phosphorus and rapidly available potassium to the amount of season fertilizer were 0.251, 0.057 and 0.180.8. Average biological yield of tobacco was 418.8g/plant, average economic yield was 171.6g/plant, economic index was 0.408; content of nitrogen, phosphorus and potassium in leaf was the highest, which were separately 45.16 ,4.49 ,72.08 kg/hm². The ratio of uptake of nitrogen phosphorus and potassium to input of nitrogen phosphorus and potassium nutrients were 0.501, 0.169 and 0.428. Average uptake of nitrogen phosphorus and potassium in tobacco plant were separately 67.67, 10.14 and 119.83 kg/hm². If the nutrients leaching and other losses were ignored in tobacco field, average nutrients excess of input nitrogen phosphorus and potassium in season were separately 33.42, 36.45 and 109.88 kg/hm².