Release of potassium, calcium and magnesium from sugarcane straw residue under different irrigation regimes

The sugarcane straw deposited in soil after mechanized harvest can be a valuable source of nutrients. The aim of this research was to estimate the nutrient release from sugarcane straw, under different irrigation regimes and duration of decomposition. The experiment was conducted in a glasshouse using 57 g of sugarcane straw, which represented a total of 10t ha-1 of straw. The straw was placed in bags made of plastic screen (mesh size 1.8mm). These bags were arranged inside the trays (total area of 567 cm2) filled with 2 dm3 of Oxisol. Experiments were designed according to randomized complete split plot: three water irrigation levels (450 mm, 900 mm and 1340 mm of water), ten sampling periods (0, 15, 30, 60, 90, 150, 180, 240, 300 and 360 days after the experiment installation), and three replicates. The dry matter accumulated from the straw subjected to decomposition, and the quantities of released calcium (Ca), magnesium (Mg) and potassium (K) were evaluated over 360 days. Sugarcane total dry mass decreased by 46% during the experiment. The nutrient release rate of potassium was 88.8%, 90.45 and 93.6% at irrigation regimes 450 mm, 900 mm and 1340 mm respectively, of calcium: 70.1%, 70.7% and 74.8% at 450 mm, 900 mm and 1340 mm respectively, of magnesium: 49.6%, 60.4% and 61.4% at 450 mm, 900 mm and 1340 mm respectively. Therefore, in regions with large amount of rainfall K application to sugarcane crop can be reduced because this nutrient can be partially supplied from the decomposed straw.