Composto orgânico: composição, mineralização e produção de cultivar de porta-enxerto de nogueira-pecã (Carya illinoinensis (Wang) K.)

Abstract

Fruit and vegetable residue (FVR) can be used for the production of organic compost, which when mineralized may provide nutrients to fruit trees, such as the Pecan (Carya illinoinensis (Wang) K.). The objective of the study was to produce an organic compound from the mixture of different ratios of fruit and vegetable residue (FVR), rice husk (RH) and poultry manure (PM) that meets the minimum quality requirements demanded by legislation, as well as to evaluate the N mineralization of the organic compound used in the composition of the substrates to be used in the production of Pecan (Carya illinoinensis (Wang) K.) rootstock cultivar. This study was divided into two studies: Study 1 (Composition and mineralization of organic compounds derived from the composting of fruit and vegetable residues) and Study 2 (Growth and nutritional status of Pecan rootstock cultivar subjected to the application of an organic compound-based substrate). In Study 1, four treatments (piles) were assembled with different ratios of mixtures of FVR:RH:PM (v:v): 2:1:0, 1:1:1, 1.5:1:0 and 1.2:1:0. The treatments were submitted to the composting process for a period of 95 days. Four organic compounds were obtained (C1, C2, C3 and C4) and analyzed using the following parameters: TOC Nt, C/N CEC/C, EC, pH, moisture content, N-NH4+, N-NO3-, and contents of P, K, Ca, Mg, Cu, S, Mn and Zn. The second stage of this study was to perform the N mineralization test of the organic compound (C2) produced in the first stage of the study, used together with agricultural peat (AP) and carbonized rice husk (CRH) in the composition of the following treatments: 40%AP+60%CRH (control), 20%AP+80%C2, 30%AP+70%C2, 40%AP+60%C2, 50%AP+50%C2, 60%AP+40%C2, 70%AP+30%C2 and 80%AP+20%C2. The contents of N-NH4+, N-NO3-, mineral N and mineralized N were analyzed in relation to the total added at each time (0, 7, 14, 28, 56 and 112 days). In Study 2, the 40%AP+60% CRH (control), 20%AP+80%C2, 30%AP+70%C2, 40%AP+60%C2, 50%AP+50%C2, 60%AP+40%C2, 70%AP+30%C2 and 80%AP+20%C2 treatments were analyzed in relation to the development and nutritional status of Pecan rootstock cultivar in the period of 112 days. In Study 1, the constant additions of fruit and vegetable residues showed no significant difference in the temperature pattern developed in the compost piles. The composting of fruit and vegetable residues and rice husk requires an external source of nutrients to produce an organic compound within the minimum standards of quality required by organic fertilizer legislation. The compost (C2) exhibited excellent performance and the results were within the standards required by legislation in the following maturation and quality parameters: C/N ratio, TOC, N, P, K, Ca, Fe, Mn, CEC/C, pH, and moisture%. The use of organic compound in substrate composition favored N mineralization in comparison to the control treatment, especially the 40%AP+60%C2 mixture, which exhibited the highest NH4+ value at all the evaluated times, and the 60%AP+40%C2 mixture with the highest NO3-, mineral N and mineralized N at 28 days after incubation, as well as the highest N mineralization during the evaluation period. In Study 2, rootstocks grown in the 80%AP+20%C2 and 60%AP+40%C2 treatments exhibited greater accumulation of dry shoot mass (DSM). The 50%AP+50%C2, 40%AP+60%C2 and 30%AP+70%C2 treatments showed a greater increase in height and in the accumulation of total dry matter (TDM). The 40%AP+60%C2 treatment promoted the highest accumulation of dry root mass (DRM) and Dickson quality index (DQI) in the Pecan rootstock cultivar. The doses of organic compound (C2) did not affect the concentration of nutrients in the leaves of pecan, except N, which exhibited a lower concentration in the leaves in all the treatments. Thus, the organic compound produced from residues of fruits and vegetables, rice husk and poultry manure is efficient in the production of pecan rootstock cultivar.