Irrigação do algodoeiro com água residuária tratada e doses de nitrogênio: efeitos sobre a cultura e o meio edáfico.

Abstract

The objective of this research was to verify the effect of wastewater and of provisioning water and of nitrogen doses on the brown cotton crop (Gossypium hirsutum L.), variety BRS 200 brown. The experiment was conducted in green house belonging to the Department of Agricultural Engineering of the Federal University of Campina Grande, Paraíba state. The levels of wastewater and of provisioning water in the soil were of 25, 50, 75 and 100% of the available water (AW) and the doses of nitrogen (N) were of 0, 150, 300 and 450 kg ha"1. The statistical design in randomized blocks was used, in mixed factorial (4 x 4) + 1, plus a proof irrigated with provisioning water with 75% of the AW and receiving 300 kg ha"1 of nitrogen, with three repetitions. The experimental unit was represented by a plastic vase containing 9 kg of soil, which was collected in the 20 cm superficial layer of the profile of a sandy-clay-loam soil. The variables relative to growth, development and production of the crop and to water consumption and edaphic medium, in terms of salinity, were evaluated. It was verified that the foliar area at the 100 days after emergency (DAE) suffered significant effect, presenting averages of 844.27 and 412.13 cm2, respectively, for the factorial and the proof. For the biomass at 100 DAE, the effect of the contrast was also significant, presenting averages of 17.44 and 10.38 g plant"1, being the largest production of biomass of 27.32 g plant"1 reached with a nitrogen dose of 228.37 kg ha"1. The maximum production of biomass of 21 g plant"1 was reached with water availability for the crop around 72%. The maximum Etc estimated in the interaction N and AW of 736 mm was reached with 86.71% of available water and nitrogen dose of 178 kg ha"1. For the electrical conductivity of the saturation extract, the factorial differed statistically in relation to the proof, with averages of 2.17 and 1.1 dS m"1, respectively. The lowest value of the sodium adsorption ratio of 4.14 was gotten with soil available water content of 73.38% and nitrogen dose of 362.48 kg ha"1. For the sodium content, the contrast between the factorial and the proof had significant effect, respectively, with averages of 13.18 and 4.88 mmolc L'1.