Land-use impact on soil solution constituents from an Ultisol of North Florida

Land use management is important to maximize nutrients use efficiency and reduce losses, especially on sandy soils. Nutrient cycling in pastoral systems is different as the grazing animals are excreting back to the pasture most of the ingested nutrients. The objective of this study was to evaluate N, P, K, Ca, Mg, and Na by monitoring elements' concentrations in soil solution from bahiagrass (Paspalum notatum Flugge) pastures continually-stocked with cattle (CP) and rotationally-grazed by goats (GP) in comparison with arable land (AL). Samples were obtained by suction cup lysimeters randomly installed at three depths in an Ultisol of North Florida, USA. To evaluate nutrients in atmospheric deposition, surface and ground waters, samples from rain, nearby spring, lake and three wells on the farm were also analyzed. The results confirmed that land-use management had an effect on soil-solution N, P, K, Ca, Mg, and Na concentrations reflecting managerial and climatic conditions. The means of these nutrients ranged widely from 0.64 to 11.14 mg L-1 for N, 0.03-0.45 mg L-1 for P, 0.12-6.97 mg L-1 for K, 0.37-33.91 mg L-1 for Ca, 0.47-7.39 mg L-1 for Mg, and 1.28-4.37 mg L-1 for Na. The soil-solution N was higher from March through August (wet seasons) and lower and relatively constant between September and February (dry seasons). The N from shallow depth (0.6 m) of CP was fourfold higher than the deep (1.8 m) one and exceeded the maximum permissible level (MPL) of 10 mg L-1. A 1.5-fold increase by depth of AL was detected, and a leaching of 53-98 kg N ha(-1) was identified for both AL and CP during the wet season vs. 4-5 kg ha(-1) leachable N from GP. Also, a 1-3 kg P ha(-1) may be leached from CP during the wet season. The nutrients in the soil solutions tended to be higher than those in rain, lake, sprint, well, and tap waters. In groundwater however, there were episodically N concentrations as high as those in the soil solution.