Sistema integrado de diagnose e recomendação (DRIS) em diferentes estádios de desenvolvimento da soja

Abstract

The fertilizers input has an important role in the soybean crop production due to its potential environmental impact and, mainly, to the impact on the production costs. Methods of nutritional diagnostic of plants based on foliar analysis helps to increase fertilization efficiency. Among these methods, the sufficiency range of foliar nutrient contents has been the most used on grain crops. Alternatively, the Diagnosis and Recommendation Integrated System (DRIS) has also been proposed to the diagnostic of plant nutrient conditions. However, the leaves analyzed in these methods are sampled on the blooming stage, which limited the time to correct nutritional problems for crops of short cycle, as soybean. Then, nutritional problems found by the foliar diagnostic are, in general, corrected in the next growing season. In this work, the anticipation of foliar nutritional diagnostic was evaluated, by using DRIS. Besides, the influence of leaves types was also evaluated. The DRIS indexes of N, P, K, Ca, Mg, S, Zn, Cu, Mn, Fe, and B obtained on the standard leave (SL) of soybean, sampled on blooming stage (R2) were compared with the indexes obtained on the following vegetative stages: V4, V5, V7, V9, and V11. On these stages, the DRIS indexes were determined on two kinds of leaves: the most mature leave (MML) and others (OL). Besides, leaves nutrient contents related to the best condition of nutrient balances was determined, by using the DRIS indexes of each nutrient. The experiment was on field conditions, on a Typic red latossol, in Passo Fundo city, RS, in the Southernmost region of Brazil. A three factorial compound be five vegetative stages (V4, V5, V7, V9, and V11), two fertilization level (with and without the NPK formula 2:25:25), and two kinds of leaves was used. A randomized complete blocks design with four replicates was used. The foliar nutrient contents were analyzed by using acid digestion, except the B content, which was obtained by dry combustion. The DRIS indexes were calculated with Beaufils, Jones, and Elwali & Gasho methodologies and by using a software from University of Passo Fundo. The DRIS norms were obtained from de standard population formed by samples of soybean (BRS 244.) with grain yield higher than 4.032 kg.ha-1. The DRIS indexes values were grouped in ranges from 10 to 10. The nutrient contents considered as the more adequate were found by using the DRIS indexes, which was assumed to range from 10 to 10 and obtained on the IL, on the R2 stage. The DRIS indexes calculated with the N, P, K, Ca, Mg, S, Cu, B, Mn, and Fe contents of the IL agree with the DRIS indexes obtained on the MML, but it changed with the soybean stage. On V7 stage, it was found with N, P, K, Ca, S, and Cu, while on V9 stage, it was found with N, K, Mg, S, B, Cu, Fe, and Mn. There was also agreement between the DRIS indexes obtained by using the OL and the IL. It was found for N, S, B e Fe, on both stages, while for Ca and Mn, on V7 stage. By using the other stages analyzed, there were a less agreements between the DRIS indexes from the IL and the other tested leaves. Besides, the indexes obtained in these stages showed a higher number of nutrients as equilibrated. Then, the anticipated diagnostic is less adequate when using these stages. The most adequate nutrient contents of the IF, on R2 stage, is: 2,08 % (N), 0,46 % (P), 2,03 % (K), 0,52 % (Ca), 0,27 % (Mg), 0,18 % (S), 42,99 mg kg-1 (Zn), 11,93 mg kg-1 (Cu), 136,69 mg kg-1 (Fe), 31,64 mg kg-1 (B) e 103, 39 mg kg-1 (Mn). It is possible to anticipate the soybean leaves diagnostic by 5 using DRIS shifting the diagnostic period from the R2 to V7 or V9 stages, but it change with the types of leaves and analyzed nutrient