Characteristics Of Nitrogen,Phosphorus And Potassium Nutrient Resources In Farmlands Of Gansu

The characteristics of N, P and K nutrients in farmlands of Gansu have not been well documented. With the object of soil production improvement and balance recommendation fertilization, and based on the black-box theory and ecological principle, the paper carried out a systematical study on the nutrient characteristics of farmland and fertilizer resources by means of combining investigations with field trials. A set of suitable regionalization for BRF was established. The results are as follows: 1. The contents of total soil nitrogen and Olsen-P in farmlands increased obviously, soil potassium content increased slightly in general and reduced in some regions. According to the monitoring results of 5064 soil sample from cultivated horizon in the province in 1998, the average content of total soil N increased from 0.80g/kg in 1983(the second soil survey) to 0.92g/kg in 1998 by 15%, with an increment of 0.12g/kg. Olsen-P rose from 7.36mg/kg by 52.0% in 1983 to 11.19mg/kg in 1998, with a net increase of 3.83mg/kg. The average contents of soil total K and available K increased from 19.5 5g/kg and 198.50mg/kg in 1983 to 21.77g/kg and 195.14mg/kg in 1998. Soil available K content was reduced in Longzhong and Longnan regions by 16.64mg/kg, 12.55mg/kg, respectively, while that was increased in Hexi and Longdong regions by 27.27mg/kg, 19.62mg/kg, respectively. 2. There was larger difference in N, P and K contents of major cultivated soil types and farmland types. Total soil N of 9 kinds of cultivated soil types varied from 1 .49g/kg to 0.74glkg with sequence: Chestnut soil>Cinnamon soil>Grey cinnamon soil> Irrigation desert soil> Red clay soil> Chao soil> Heilu soil> Loessal soil> Irrigation-warping soil. The total N of dry-land soils is higher than that of irrigated soil in different farmland types. The average content of soil alkali-hydrolyzable nitrogen ranged from 63.0mg/kg to 124mg/kg. The Olsen-P contents of 7 kinds of cultivated soil types is: Chao soil(15.47mg/kg) ~?Chestnut soil> Irrigation desert soil> Heilu soil> Grey cinnamon soil> Red clay soil> Cinnamon soil(9.Olmg/kg). Olsen-P of irrigated land soils is 6 times as high as that of dry-land soils, which reflected imbalance of phosphorus fertilizer application in (lansu province. The range of available K content m 10 kinds of cultivated soil types is from 163.79mg/kg to 268.86mg/kg, with the sequence: Chestnut soil> Chao soil> Irrigation desert soil> Irrigation-warping soil> Red clay soil >Sierozem> Heilu soil > Loessal soil> Cinnamon soil. The soil available K content of vegetable land and irrigation land was the highest in different farmland types. 3. The input quantities of nitrogen, phosphorus and potassium nutrients increased gradually in past about 50 years, but the nutrient constitution from organic manure and chemical fertilizers changed largely in different ecology-regions farmlands of Gansu. Input of N, P205 and 1(20 in 1953 was supplied completely by organic manure, wihle in1999 it was 29.1%N, 15.36% P205 and 73.58%K20, respectively. The input of Nitrogen , phosphorus and potassium fertilizers was 14.05 X 104t in 1980, with N: P205: K20 ratio of 1:0.36:0.05. the total amount applied of chemical fertilizer arrived at 63.4 X 104t (pure nutrient) in 1999, N, P205 and K20 occupied 54.5%,42.1% and 3.5% respectively, with N: P205: 1(20 ratio of 1:0.77:0.06. The effect of N and P on yields decreased, but that of K has appeared out. The chemical fertilizer use amount per unit area shows an upward tendency. N use amount was 99.6k...