Nutrient leaching in Oxisols under native and managed vegetation in Brazil

Brazilian savanna Oxisols are prone to nutrient leaching because of low nutrient retention and high water conductivity. We determined downward and upward fluxes of Ca, Mg, K, NH4-N, and NO3-N at 0.3-, 0.8-, and 2.0-m soil depths under native savanna vegetation (Cerrado), Pinus caribaea Morelet plantation, managed productive Brachiaria decumbens Stapf pasture, degraded B. decumbens pasture, conventional tillage, and no-till corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] cropping using exchange resin cores, and set up a nutrient budget using previously published input data. At each of the study depths, we installed three to six PVC tubes (0.10 m in diameter, 0.11 m in length) filled with a mixture of field-fresh soil and HBr-washed ion exchange resin (Amberlite MB-20, 10:1 v/v), which were removed and extracted after 2 yr. Downward fluxes at 2-m soil depth ranged from 0.22 to 2.3 g Ca, 0.02 to 0.71 g Mg, 0.08 to 1.17 g K, not detected (n.d.) to 0.96 g NH4-N, and n.d. to 4.4 g NO3-N m(-2) yr(-1). Upward fluxes, because of capillary rise, frequently amounted to 30 to 50% of downward fluxes. At 0.3-m depth, net leaching fluxes of Ca in the cropping systems and productive pasture (2.3-4.9 g m(-2) yr(-1)) and of K and NO3-N in the cropping systems (K: 0.73-0.85, NO3-N: 2.3) were significantly higher than in all other systems except for NO3-N in Pinus (Ca: 0.02-0.18, K: 0.09-0.15; NO3-N: n.d.-0.70). In forests and pastures, all nutrients accumulated on balance while in cropping systems budgets were balanced or negative except for N. To reduce these losses, timing of fertilizer amendments should be optimized and in the no-till system evaporation and fast water fluxes reduced for example, by stubble mulching.