Funções de resposta da cana-de-açúcar, fase soca, a níveis de irrigação e adubação de cobertura.

Abstract

With the objective of evaluating the influence of water depths, levels of manuring and its interaction on the economical income of alcohol, components of production and growth of the sugar cane {Saccharum officinarum L.), cv SP 791011, an experiment was carried out in a soil Red-Yellow Podzolic, in the period from 2003 to 2005, in the Farm Capim at the Miriri distillery, in the municipality of Capim, Paraíba State. The experimental design was randomized blocks, in 4x4 factorial with four repetitions. The treatments was constituted of the combination of four irrigation levels applied through an mobile center pivot irrigation system, in intervals of twelve days, in the amounts: Lo (without irrigation); Li (13.8 mm); L 2 (27.5 mm) e L3 (41.3 mm). The manurings were composed of the elements N and K20, in the amounts: A0 = 0; A] = 90; A2=180 e A3 = 270 kg ha"1. To growth analyzes five destructive collections of plant were accomplished, in cycle of fourth ratoon, in harvest 2004/2005, at 74, 120, 210, 287 and 387 days after cutting, for each water treatment and a treatment of manuring (A2). After analyzes of the results was verified that in severe conditions of water stress has a change in standard of tillering of the sugar cane and that the water deficit reduced the efficiency in exportation of assimilated produced in leaves for other parts of the plant. During the cycle of 3t h ratoon the average productivity of stalks was significantly influenced by the factors water depth and manuring and not significantly for the interaction L x A. Already for the cycle of 4t h ratoon, there was significant answer for irrigation, manuring and interaction L x A. The largest incomes in stalks obtained in the 3t h ratoon had propitiated a larger water use efficiency (WUE) in comparison with to 4t h ratoon. It was observed that to WUE in the two cycles had been smaller in the treatments not fertilized (Ao), demonstrating a harmful effect of the absence of manuring in the WUE. The response function of the sugar cane, in relation to the water depth supplied in 3t h ratoon, inside of manuring levels, presented a maximum point in L m (A3) = 1,360.12 mm with income in alcohol of 9,243.54 L.ha"1, providing a net revenue of R$ 4,434.12 ha"1. Already the maximum economy was reached in L* (A3 ) = 1,341.37 mm with productivity of 9,234.82 L.ha"1, that provided a net revenue of R$ 4,441.52 ha"1, for a relation of cost CJCy = 0.93. In function of levels of fertilization inside of water depths in 4t h ratoon, the response function presented point of maximum in Am (L3) = 425.68 kg.ha"1 with yield of 8,354.16 kg.ha"1 providing a net revenue of R$ 4,568.51 ha"1 and point of maximum economy A* (L3) = 382.10 kg.ha"1 with productivity of 8.312, 56 L-ha"1 and net revenue of 4,610.57 ha"1, for the cost relation PA/PY = 1,91.