The intensive production of herbage for crop-drying IV. The effect of massive applications of nitrogen with and without phosphate and potash on the yield of grassland herbage

Abstract

1. A small-scale plot experiment was carried out from 1947 till 1949 to study the effect of massive dressings of nitrogen with and without phosphate and potash on the yield of a ryegrass-dominant sward. A 4 × 4 Graeco-Latin square was used.The nitrogen treatments were: (1) no nitrogenous fertilizer, (2) 260 lb., (3) 520 lb., (4) 416 lb. nitrogen per acre per annum. These applications were divided into four or five equal dressings, the first being applied in March and the others after successive cuts.In 1948 and 1949 the following mineral treatments were also applied: (A) no mineral fertilizer, (B) 180 lb. K2O per acre, (C) 120 lb. P2O5 per acre, and (D) treatments B and C combined. These treatments were applied in two parts, half in spring and half in midsummer.2. Applications of phosphate did not affect the yields of herbage but yields were severely restricted in the absence of potash.3. Where potash was applied there was no significant change in the annual yield of herbage from 1947 to 1949 for any one of the treatments. The nitrogen treatments increased the yields from 4300 lb. dry matter and 600 lb. crude protein per acre with treatment 1 to 9000 lb. dry matter and 1900 lb. crude protein with treatment 3. The yield response of dry matter to nitrogen applications was curvilinear, but that for crude protein was rectilinear.4. Increasing the application of nitrogen per cut from 52 to 104 lb. per acre raised the protein content in the dry matter of the herbage from 15·20 to 18·25%.5. The plots receiving the nitrogen treatments gave earlier production and also produced a greater proportion of the total yield in July-September than the untreated control plots.6. Where potash was present the average net efficiency of recovery of nitrogen for 3 years was 47, 39 and 37% for treatments 2, 3 and 4 respectively.7. Where potash was present the content of vigorous grasses in the sward (perennial ryegrass and timothy) was increased in relation to the quantity of nitrogen applied, from approximately 40% in treatment 1 to 75% in treatment 3. The content of vigorous grasses in the sward was reduced in the absence of potash.8. The results and their practical implications are discussed.