Ratoon sugarcane response to potassium is dependent on the environmental conditions of the region. Cropping systems that do not burn crop biomass after harvest leave crop residues on the soil, affecting the soil-plant nutrient dynamics system and fertilizer requirements. The objective of this study was to evaluate the effect of potassium fertilization of first and second ratoon sugarcane crops on potassium contents in the soil, in the plant, and yield and quality of stalksin an Oxisol under a conservation cropping system. The following potassium rates were tested: 0, 27, 54, 108, and 162 kg K ha-1, arranged in a randomized block design with five replicates. The application of potassium increased soil nutrient concentrations at six months, reaching 2.87 and 2.61 mmol c dm-3 with the highest rate in the first and second ratoons, respectively. The increase in available exchangeable-K content in the soil favored a greater plant uptake of this nutrient, reaching 12.1 and 10.0 g kg-1 in the first and second ratoons, respectively. The increase in potassium absorption by plants was reflected in the production of stems; the highest yields (87.0 and 132.9 t ha-1) were obtained with the application of 162 kg K ha-1 in the first and second ratoons, respectively.

The presence of mulch on the soil surface after the mechanical harvesting of sugarcane (Saccharum officinarum L.) enhances the cycling of nutrients, especially K, which can decrease K fertilizer recommendations for the crop. The aim of this study was to evaluate the effect of K addition to an Oxisol, with an initial concentration 0.07 cmol c K kg-1, in first and second ratoon (no-till) sugarcane cultures by a conservationist system, i.e. rational use of fertilizers, use of alternative inputs and especially the maintenance of residues in soil that was previously burned to facilitate cutting. The following K doses were tested: 0, 32.5, 65, 130, and 195 kg K2O ha-1, arranged in a randomized block design with five replicates. Potassium content in the soil and in the plant, as well as the yield and the quality of stalks were evaluated. Soil K application increased K concentration in soil and plant, and was reflected in the production of stalks, with higher production (87.5 and 107.5 t ha-1) with the use of 120 and 123 kg K2O ha-1 in first and second ratoon sugarcane, respectively. At the first 2 yr it was not possible to reduce the K fertilization in ratoon. Therefore, with the introduction of the conservationist system there was an increase (20 t ha-1) at the second ratoon regarding the first one with the same applied rate.

São restritas as informações sobre a resposta de soqueiras de cana-de-açúcar à aplicação de nitrogênio em colheita sem a despalha a fogo. Diante deste contexto, objetivou-se avaliar a nutrição nitrogenada em soqueiras de cana-de-açúcar, em sistema de colheita sem queima, através de análises químicas do solo, da diagnose foliar, de avaliações biológicas (altura da planta, diâmetro de colmos e número de colmos industrializáveis e da produtividade de colmos). Para esse estudo, instalou-se um experimento em campo, na Fazenda Experimental Santa Terezinha, município de Jaboticabal (SP), em soqueira de cana-de-açúcar cultivar SP 79-1011, em Latossolo Vermelho distrófico, com as doses de nitrogênio: zero; 50; 100 ; 150 e 200 kg ha-1 de N. Os tratamentos foram aplicados após o corte da cana-planta em junho/2005. Foram avaliados durante os dois primeiros cortes da soqueira de cana-de-açúcar a fertilidade do solo (camadas 0-20 e 20-40 cm), o estado nutricional, o desenvolvimento e a produtividade de colmos. A adubação nitrogenada em soqueira de cana-de-açúcar promoveu acidificação do solo restrita à camada superficial (0-20 cm); entretanto, não aumentou significativamente os teores de macro e micronutrientes nas folhas, exceto o N na segunda soqueira. A resposta das duas primeiras soqueiras de cana-de-açúcar à aplicação de nitrogênio, em sistema de colheita sem queima, ocorreu apenas no segundo corte. A dose de 200 kg ha-1 de N promoveu aumento no desenvolvimento da cultura, na nutrição da planta e na produtividade de colmos da soqueira da cana-de-açúcar.

Information about the responses of sugar cane ratoon to nitrogen application in harvest without the use of fire are restricted. The objective of this work is to evaluate nitrogen nutrition in sugarcane ratoons in harvest without the use of fire through chemical analysis of soil, foliar diagnosis, biological evaluations - plant height, stalk diameter and number of industrialized stalks - and production of stalks. A field experiment was setup at Santa Terezinha Experimental Farm in Jaboticabal (SP), with sugarcane ratoons cv. SP 79-1011, planted in a dystrophic Rhodic Hapludox with nitrogen doses of: zero; 50; 100; 150 and 200 kg ha-1 of N. The doses were applied after sugarcane harvest in June 2005. During the two cuts of sugarcane ratoon, soil fertility in the layers of 0-20 and 20-40 cm, the plant nutritional condition and the development and production of stalks were evaluated. Nitrogen fertilization of the sugarcane ratoon increased soil acidification only in the superficial layer (0-20), however it didn't raise significantly macro and micronutrients in the leaves, except for N in the second ratoon. The response of the two first sugarcane ratoons in relation tonitrogen application in harvest without burn occurred only in the second cut. The dose of 200 kg ha-1 of N enhanced development of the crop, nutrition of the plant and production of stalks of sugarcane ratoon.