Role of soil mineral nitrogen for agricultural crops: Nitrogen nutrition diagnostics in Lithuania

Abstract

We validated: (i) the significance of mineral nitrogen present in the soil for diagnosing the agricultural crops need for fertilization, and (ii) the environmental effects of N. These were achieved by conducting field and laboratory experiments under Lithuanian agro-climatic conditions. The yield of agricultural crops correlated most strongly with mineral-N, somewhat less with nitrate-N and least with ammonia-N. Crop yields correlated most strongly with mineral-N amount measured in spring (April) in the 0 – 60 cm soil layer. Crop yields and the efficacy of N fertilizer depends on the amount of mineral-N in soil; when its amount increases, plant yield increases and there is a subsequent decrease in the efficacy of mineral fertilizers. Calculation of the rates of N fertilization in spring should be based on the amounts of mineral-N present in soil. Calculation of crop need for additional N fertilization should be based on the results of plant chemical content analysis. The crop should be fertilized additionally when total N in plant dry matter is <35 g kg−1, N:P ratio <9.0 and K:N ratio >0.90.