Nitrogen fertilization and harvesting intervals affect yerba mate productivity and the nitrogen and carbon of soil

Leaves (FO) and thin branches (GF) are the main plant components harvested from Ilex paraguariensis (mate) plantations, leading to high exportation of nutrients, among them, the nitrogen (N). Scientific and technical information are scarce to support fertilizer recommendation aiming to replenish N exportation and to sustain mate productivity. Thus, this study aimed to evaluate the influence of N fertilization and harvest intervals on N and organic carbon (CO) content in the soil and on mate productivity and N content. The experiment was conducted in São Mateus do Sul, Paraná state, Brazil, in a seven-year old mate plantation established on an Oxisol, where we evaluated the effect of 0, 20, 40, 80, 160, and 320 kg ha^-1 of N, for harvest intervals of 12, 18, and 24 months. Nitrogen (NL) and CO (COL) in the labile and total (NT and COT) forms were determined in the soil at depths of 0-10, 10-20 and 20-40 cm. Harvest consisted in the removal of 95 % of the tree crown sprouted from the previous harvesting. The green material collected was evaluated individually for the components FO, GF and thick branches (GG), being FO+GF the commercial mate product (ECOM). We also evaluated the plant component relationships between green/dry weights (MV/MS), as well as the contents of N in FO, GF and GG. The positive effect of N fertilization on NL and COL contents in the soil was more expressive for the shortest harvesting interval, and was negative or null for the 24-month interval. Nitrogen doses increased the content of NT in the largest harvest interval and reduced the yield for 12 months; COT was not influenced by fertilization. We observed increased productivity with N doses, and the most significant responses occurred in longer harvest intervals. The interval of 12 months between harvests is insufficient for the plant recovery from the previous harvesting impacts. The 18-month interval is more recommendable because the plant is well nourished in N. Nitrogen does not affect the water content of the commercial green yerba mate, which is more affected by the time between harvests. The leaf N content between 33.0 and 37.0 g kg^-1 may indicate well-nourished plants, regardless the harvest interval.

Keywords:
Ilex paraguariensis; Efficiency of nutrient use; Harvesting handling; Organic matter of soil