Nutrient Diagnosis on Young Stands of Slash Pine by DRIS

A comparative nutrient diagnosis on young stands of slash pine by DRIS and critical concentration value approach(CCVA)was conducted.The results showed that the DRIS produced more accurate nutritional diagnos is than that by CCVA when diagnosing phosphorus nutritional status in leaves. That is,the phosphorus application enhanced the growth of slash pine and the growth was significantly interrelated to phosphorus DRIS indexes,but there was no response for phosphorus concentration in leaves. DRIS diagnosis was also influenced by the age of trees and site environment as the CCVA. So, high-yield populations for calculating diagnosis parameter should be chosen from the stands of the same age at the local site. According to the diagnosis results by DRIS,the mechanism of N P K fertilizers to the growth of young slash pine was considered as follows:N application increased the N concentration and the unbalance of leaf nutrition and was not benefitable to the growth.The application of calcium-magnesium phosphate alone at the rate of P 21.82 kg/hm2 would improve the N,P,Ca and Mg nutritional status in leaves significantly, reaching the optimum balance. Besides,it was found that P nutritional status in the control treatment was obviously improved in the third year after planting,indicating the young trees were able to use soil P to meet the need of P for their growth.