Fertirrigação com água residuária na cultura do algodão de fibra marrom.

Abstract

The objective of the work was evaluate the effects of fertirrigation with treated domestic wastewater on cotton plant of brown fiber, involving aspects related to its growth, development and production, and on soil chemical properties, with increasing irrigation water depths and in presence and absence of nitrogen and phosphorus fertilization. The field research was conducted in the dependences of the Station of Treatment of Sewers of the Company of Water and Sewers of Paraíba, located in the neighborhood of Catingueira, distant 10 km of Campina Grande downtown, Paraíba state, Brazil. The experimental design was in randomized blocks in a mixed factorial scheme (4 x 2 x 2) + 2, whose factors were four irrigation water depths with effluent (781, 643, 505 and 367 mm), absence and presence of nitrogen and phosphorus in the doses of 0 and 90 kg ha-1 of N and 0 and 60 kg ha-1 of P2O5, and two additional treatments fertilized with nitrogen in the doses of 90 and 180 kg ha-1, both irrigated with water of public provisioning with irrigation water depth of 643 mm. The growth and development of the cotton plant were superior when the treated domestic effluent was used, with better results for the irrigation water depth of 781 mm. There was not need for complemented fertilization with nitrogen and phosphorus in the soil containing 0.38 g kg-1 of nitrogen and 13.4 mg dm-3 of phosphorus with domestic effluent containing 60.5 mg L-1 of total nitrogen and 4.6 mg L-1 of total phosphorus. The weight of the cotton in pit, of the fiber and of the seed were also superior for the largest irrigation water depth (781 mm) with treated domestic effluent in the absence of chemical fertilizer. There was not detriment in the textile characteristics of the fiber, when effluent from treated domestic sewer was used in the irrigation of the cotton plant of brown fiber. The fertilization with nitrogen and phosphorus, respectively, in the amounts of 90 and 60 kg ha-1 were supplied with the use of the wastewater in the irrigation of the cotton plant. Contents of lead and cadmium were found in the cotton plant leaf at the 85 days after the emergency of the seedlings. The contents of P, K+, Ca2+, N, H, organic matter, and the cationic exchangeable capacity of the soil increased after the cultivation, already the pH, Mg2+, Na+, C, exchangeable sodium percentage, sum of exchangeable bases, and the saturation percentage by bases decreased. The values of the electrical conductivity, pH, contents of Ca2+, Mg2+, Na+, Cl-, and the sodium adsorption relationship of the soil stratum saturation decreased after the irrigation with treated effluent and after 646 mm of pluvial precipitation. The cotton plant of brown fiber irrigated with effluent from treated domestic sewer obtained great economical incomes, which were more pronounced when it was not used nitrogen and phosphorus fertilizer