Manure and Management Affect Grassland Production and Soil Quality in Organic Lamb Production

Core Ideas Effects of small applications of manure on soil quality will persist for 10 yr. Designating grassland use as pasture only will maintain productivity and soil quality. Using grassland for hay will increase production and lower soil quality. Grasslands occupy many hectares of hill land. Little research has been published on grassland management on such land. Two farming systems, producing spring lamb, were compared in the 10‐yr experiment reported here. Treatments were low and high external inputs with three replications. Animals were on the grassland all year, from which they obtained over 90% of annual feed requirements. Manure was applied in Years 1 and 3 to the fields under high‐external‐inputs treatment. Herbage mass accumulation, botanical composition, lamb performance, and soil quality were measured. Three grassland uses were applied to each of one‐third of the area of each system and were designated pasture, buffer, and hay uses. Pasture‐use fields were grazed only. Hay‐use fields were harvested twice for hay and grazed. Buffer‐use areas were harvested for first‐cut hay and grazed. Fields receiving manure accumulated almost 10% more herbage mass and produced almost 30% more lamb ha −1 than fields receiving no manure. Pasture use fields had less grass and more forbs and dead material than buffer and hay uses. Available P, K, Ca, and Mg were greater on manure‐applied fields. Available K and Mg were greater on fields used for pasture compared with hay use. Application of manure (annual addition of 15, 5, and 12 kg ha −1 N, P, and K, respectively), a higher stocking rate, and dividing the grassland resource into pasture, buffer, and hay uses increased lamb production up to 30%ha −1 annually without affecting production per animal.