A preliminary study on richlack index of soil available P for alfalfa in Huanghua City

There are over 7 000 ha alfalfa planted in Huanghua city, Hebei province, but local alfalfa fertilization is lack of scientific guidance. The richlack indexes of soil nutrients are widely used in the world to determine appropriate fertilizer application rates due to they are very simple and convenient to be used in practice. In order to establish the richlack indexes of soil nutrients for alfalfa, a pot experiment was conducted in Huanghua city to preliminarily determine the richlack index of soil available P of alfalfa. Soils taken from 11 different farmland, which have big range in available P content, were used in this trial. The experiment was arranged for complete fertilizer treatment (CFT) and complete fertilizer except P treatment (CFEPT). The regression analysis was done according to the relative yield (RF) the yield of complete fertilizer except P treatment divided by that of complete fertilizer treatment and soil available P content. The results showed that the 1st to 6th level of soil available P in Huanghua city, corresponding the relative yields 95%, 85%-95%, 75%-85%, 65%-75%, 55%-65%, 45%-55%, were＞47.5、27.2-47.5、15.6-27.2、8.9-15.6、5.1-8.9 and 2.9-5.1 mgkg-1, respectively.