Effect of fertilization on nutrient leaching loss in garden soil

This study evaluated the effects of different fertilization rates on soil soluble NPK nutrient concentrations using pot experiments and soil leakage solution testing. The results from trials of water convolvulus （Iponoea aqatica）and flowering Chinese cabbage（Brassica parachinensis）showed that soil NO3--N, total P and K+ concentrations were non-linearly related with N, P, K application rates or their loss quantity in present season, but the relationship was linear at low to middle fertilization rates. There was positive linear correlation between fertilizer loss quantity in present season and nutrient concentrations of soil leakage water. Therefore, the concept of “bi-rate turning point” was put forward to evaluate nutrient loss potential of garden soil. In case of fertilization rates or fertilizer loss quantity over the bi-rate turning point X0, nutrient concentration of soil leakage water increased non-linearly. So, N, P, K application rates shouldn’t be over X0 for environmental protection. Based on present nutrient loss quantity, pot experimental results of gray soil, gray yellow soil and yellow soil showed that the X0 of N were 0.35, 0.32 and 0.34 g per pot, respectively; X0 of P were 0.06, 0.06 and 0.09 g per pot, respectively; X0 of K were 0.17 and 0.18g per pot, respectively, for gray soil and gray yellow soil. These values were positively correlated with the X0 of N, P and K application rates based on nutrient concentration of leakage water. Most of the X0 of N, P and K fertilization rates for environmental protection were lower than the economically optimum fertilization rates for high yield. The parameter of fertilizer loss quantity in present season was easy to obtain and was recommended as a basis for environmental protection fertilization.