Tissue Nitrogen as a Base for Recommendations of Additional Nitrogen to Spring Wheat in Southern Finland

Abstract

Nitrogen (N) deficiency has become more common in the traditional wheat cultivation areas of southern Finland as yield potentials have increased. Based on data for the period studied (1968-88) a grain protein concentration below 11.2% in spring wheat (Triticun aestivum L.) is an indicator of N deficiency. The mean of maximum grain yield obtained was 4655 kg ha^?1 when grain protein concentration exceeded 11.2%. The estimation of plant tissue N content could be an effective diagnostic tool for identifying N status in the early growth stages of spring wheat. To address the feasibility of this test, the present study was conducted in 1990-91 to determine the critical plant tissue N concentrations of three plant parts at the early double-ridge stage (Stage 2), at the stage when stigmatic branches of the carpel begin to form (Stage 7) and at pollination (Stage 10). Nitrogen was applied at rates of 0 and 110 kg N ha^?1 as granular ammonium nitrate and granular slow-release-nitrogen fertilizers to establish a wide range of plant tissue N levels, grain yields and grain protein concentrations. Critical plant N levels were calculated for the different plant parts using the Cate-Nelson procedure. From this study it can be concluded that the critical N level recommended for Stage 2 is 43 g of N kg^?1 dry matter of the whole plant. Critical N levels recommended for Stage 7 are 28 g of N kg^?1 dry matter of the whole plant, 30 g of N kg^?1 of the leaves and 13 mg total N in dry matter. Critical N levels recommended for Stage 10 are 12 g of N kg^?1 of the whole plant, 23 g of N kg^?1 of the leaves and 15 mg total N in dry matter.