Yield of white clover and its fixation of nitrogen as influenced by nutritional and soil factors under controlled environment conditions

Abstract

AbstractWhite clover (Trifolium repens L. cv. Blanca) was grown in 21 UK soils. Yield and N concentration in the herbage (leaf + petiole) were determined at six successive harvests and were related to the supplies of major nutrient elements (as indicated by analysis of the herbage) and to various soil properties. The amount of N2 fixed was estimated by subtraction of the soil N supply from the total amount in the clover.The results suggest that critical concentrations (i.e. concentrations just less than those required for maximum growth) of K, Ca and S in the leaf + petiole after 4 weeks regrowth were approximately 1.4%, 1.3% and <0.16% respectively. The relationship between herbage yield and concentration of N suggests a critical concentration in leaf + petiole of about 3.5% N; lower values probably reflect sub‐optimum rates of N2 fixation and higher values, a restriction of clover growth per se. A reduction in herbage yield attributable to deficiency of K and/or Ca appeared to occur on some soils at harvests 5 and 6, but for any one soil, yield changed little between harvests 2 and 4 inclusive. Differences in herbage yield and in the amount of N2 fixed over this period were, therefore, examined in relation to various soil properties. Significant positive correlations were obtained between herbage yield and contents of clay, organic matter, water content at 100 cm tension and cation exchange capacity. The amount of N2 fixed was less closely correlated than was herbage yield with these soil properties.