Use of chlorophyll meter in the management of nitrogen fertilization of palisade and guinea grasses

Abstract

Aiming to evaluate Sufficiency Nitrogen Index (SNI) as criteria for management of nitrogen fertilization of palisade grass (Brachiaria brizantha cv. Marandu) and guinea grass (Panicum maximum cv. Mombaça), two trials (one for each grass) were carried out using 14-dm3 pots filled with soil classified as Red-Yellow Latosol with umbric A-horizon under environmental conditions. Trials were arranged in a completely randomized design with seven treatments defined according to SNI: reference (REF), control (TEST): 0.96 (T1); 0.93 (T2); 0.90 (T3); 0.87 (T4) and 0.83 (T4), with four replicates, totalizing 28 parcels per trial. Within REF treatment, parcels were fertilized with 133.34 kg N/ha in two applications, the first was in the 1st Day of the Experimental Period (DEP) and the second was done after the first cut for grass evaluation (28th DEP). The TEST parcels were not fertilized with N. Within the other treatments, parcels were N fertilized through the experimental period only when the calculated SNI of the parcels were below to the SNI chose as criteria for fertilization. Thus, at the end of the experimental period the total amounts of N (kg N/ha) used in the treatments T1, T2, T3, T4 and T5 were, respectively: 160.00, 80.00, 120.00, 80.00 and 80.00 (palisade); and 133.34, 0.00, 120.00, 80.00 and 80.00 (Guinea). The grasses were evaluated at the cut ages of 51 and 43 days (related to the 28th and 70th DEP) considering the height at cut (cm), dry matter yield (kg DM/pot) of aerial portion (DMYAP), of root (DMYR) and total (TDMY); DMYAP accumulated in two cuts, ratio DMYAP/DMYR and efficiency of N conversion to DMYAP. The adjustment of N fertilization of palisade and guinea grasses with SNI basis allowed grasses to express in a similar way in terms of cut height and DMYAP accumulated. In relation to DMYR, lower yield was observed in non-fertilized TEST parcels, which had effect on TDMY and in the ratio DMYAP/DMYR. Considering the efficiency of N conversion to DMYAP, we conclude that the Sufficiency Nitrogen Indexes (SNIs) more adequate to adjust N fertilization of palisadegrass and guineagrass were 0.87 and 0.83, respectively