Impact of management practices on chestnut grove nutrient budgets

A 4-year study in two adjacent chestnut groves, within Northern Portugal, examined the effect of intensifying management, by means of fertilization, pruning and tilling, on the quantity of litter production and on soil macronutrient inputs and outputs. One of the stands (F) was fertilized, pruned and tilled 3-4 times per year, while the other (NF) was only tilled 2-3 times. Total litter biomass was similar in both plots but in the NIT plot leaves were the main component, while in the F plot fruits made the highest contribution to total litter. Management intensification increased nut production by an average of 50%. In the F plot, the biggest proportion of N, P K and S released by the trees was in nuts while in the NIT plot it was in leaves. Due to the low concentration of Ca and Mg in fruits, on both plots, these nutrients were released in higher amounts in leaves than in fruits. Nutrient output by leaching was low even in the F plot despite fertilization and a more intense soil cultivation. These results may be related to the small amounts of fertilizer applied and to the capacity of these ecosystems to conserve nutrients. The unusual low N loss, even when it was applied, suggests that N may be in short supply. In both plots, the 4-year average nutrient budgets were positive. In the NF plot fruit nutrient export was replenished by natural inputs. In the F plot the applied fertilizers and the natural nutrient inputs were enough to compensate for the higher nutrient output mainly due to the increased nut production and pruning. These results showed that intensification of management has contributed to an increase of fruit production and the low rates of fertilizers added were enough to minimize losses by leaching. Removal of pruned biomass, however, was not a suitable practice due to the high nutrient outputs. The finer material, the richest in nutrients, should at least be left on the soil.