Soil macronutrient distribution in rotationally stocked kikuyugrass paddocks with short and long grazing periods

Grazing management affects plant growth and animal production and it may in fluence the redistribution and cycling of nutrients excreted in dung and ur ine. Unfortunately, the soil component of pasture systems has received litt le attention in most grazing trials, and when considered has been evaluated on pastures smaller than those used commercially. A naturalized kikuyu (Pe nnisetum clandestinum Hochst, ex Chiov.) grassland was grazed by heifers (B os taurus) for 2 yr in Experiment 1 to determine the effects of two rotatio nal stocking methods (short vs. long grazing periods) on soil distribution of extractable nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), m agnesium (Mg), and sulfur (S) in 4-ha paddocks with natural shade. Addition ally, in Experiment 2, kikuyugrass-greenleaf desmodium (Desmodium intortum Urb.) paddocks were used to evaluate the effect of distance from waterers o n soil nutrient distribution in rotationally stocked paddocks (long grazing periods) without shade in a cooler, higher elevation, environment. In Expe riment 1, soil N, P, and K distribution did not differ between lengths of g razing period when assessed using a zonal soil sampling procedure with zone s based on distance from shade and water sources. These nutrients, and in p articular K, accumulated within 15 m of shade, but did not accumulate signi ficantly around waterers. In Experiment 2, zonal soil sampling indicated th at P, Mg, and especially K, accumulated within 15 m of the waterer. In both studies, extractable K data collected via a grid sampling regime and conto ur maps constructed from these data supported, in general, the conclusions made using zonal sampling. It is suggested that in this subtropical environ ment the magnitude of excretal N, P, and K accumulation is greater around s hade than waterers, and that in paddocks without shade substantial amounts of P and K accumulate near the waterer. As with small paddocks/pastures, zo nal soil sampling appears to be a practical sampling strategy for large pad docks (4 ha).