Níveis de adubação N-P-K sobre o manejo da desfolhação do capim-marandu orientado pela interceptação da radiação

Abstract

Knowledge of the morphological and physiological responses of the plant on the specific soil and climatic conditions of each region is fundamental for determining management of defoliation recommendations and more efficient fertilizer to encourage the soil-plant interface. The objective was to evaluate the best time to cut the palisadegrass Marandu (Urochloa brizantha cv. Marandu) submitted to different levels of fertilization (zero-00:00:00, low-100:32:100, medium-170: 55 170 and High-240:78:240 N-P2O5-K2O) associated with different times of defoliation (90, 95 and 100% light interception) for different seasons (transition dry/water - D/W, period of the water - W and the water/dry - W/D). Therefore we conducted two studies, the first to determine the effect of fertilizer levels and the second to assess the effect of interception of photosynthetically active radiation - IRPA on the performance of palisadegrass Marandu the seasons. The work was composed of portions of 4x3 m² with three replicates per treatment, which were distributed in a completely randomized design (CRD). The first work was evaluated in repeated measurements over time and the second in a factorial arrangement 4x3. The tiller population density (TPD tiller-1 m2), height (cm) and leaf area index (LAI m2 m2) were strongly influenced by fertilization strategies but were stable after the first evaluation. The senescence rate leaf (SRL) has shown to be quite variable with the seasons, in which the lower fertilization had an increase in 30,2% daily SRL compared to higher fertilization. The leaf elongation rate (LER mm tiller-1 day-1), stem elongation rate (SER mm tiller-1 day-1) and Phyllochron (PHYLLO days-1 sheet-1) were influenced by the seasons of the year, which provided the highest LER and SER at the time D/W, the PHYLLO tended to decrease with increasing soil fertility and on average the lowest value of 9,6 days-1 leaf-1 obtained for the high fertilization and among the seasons the lowest value obtained for PHYLLO was at the station D/W with an average of 9,1 days-1 leaf-1. The lifetime leaf (LTL days) was not flexible to treatment, the length of sheath (LS mm tiller-1) and the number of living leaves (NLL sheets-1 tiller-1) proved to be greatly influenced by the treatments and especially the time of year where the largest LS was obtained at the station D/W with an average of 359,6 mm-1 tiller-1, provided mainly by the low number of tillers that resulted in higher LS to reach the goal target 95% of IRPA and for the same period showed the highest NLL with an average of 4,9 leaves-1 tiller-1. The total dry matter (TDM kg ha-1) of leaf blade (DMLB kg ha-1), stem (DMS kg ha-1) and dead material (DMDM kg ha-1) were influenced by the treatments, which both rise fertility as the interception of light increased the production of dry matter (DM), however, the increase provided after LAIcrítical was mainly due to the increase of stem and dead material, and this response promoted the reduction in the ratio L/S, which resulted also decreasing the SPAD index, which rose from 18,3 in 90% IRPA to 11,2 in IRPA 100%, this fall, demonstrates reduction in the nutritional status of the plant. The accumulation rate of forage (ARF kg ha-1 day-1) was influenced by fertilization strategies, where most fertilization provided an increase of 204,6% in ARF compared to zero dose. Thus, we conclude that the morphogenetic and structural characteristics of palisadegrass Marandu and their forage production are strongly influenced by growing seasons and the management of fertilization is fundamental to the realization of fertilization associated with favorable environmental conditions for good forage production both quantitative and qualitative. Finally, the next time the canopy 40 cm coincides with the LAIcrítico, which is the optimal time for the defoliation of the plant under edafoclimatic factors tropical conditions.