Efeitos da aplicação de água residuária doméstica tratada e adubação nitrogenada na cultura do algodoeiro herbáceo (Gossympium hirsutum L.r. latifolium Hutch.) e no meio edáfico.

Abstract

Usually domestic wastewater contain nutrients above demand for great number of cultures and its agricultural application can provide significant reduction of fertilizer consumption besides demand alleviation and preservation of water supply. The objective of this dissertation was to evaluate cotton culture and to understand the soil environment by use of wastewater irrigation treated by a system of ponds. The cultivar BRS 187 8H (Gossypium sp) was observed, culture of great importance to Brazilian Northeast region. The experiment was conducted at field conditions on the Wastewater Treatment Plant (ETE) facilities of Campina Grande Prefecture, Paraiba State, on Paraiba Water and Sewerage Company (CAGEPA). The experimental Randomized Blocks Design was considered with 12 treatments and 4 repetitions with treatments number derived from mixed factorial [(2x5)+2] and factors from two water classes (supply and pond system treated wastewater), 5 nitrogen dosages (0, 60, 90, 120 and 180kgN/ha) with initial soil dosages of P and K (40kg/ha and 20ka/ha) and two absolute witnesses. Wastewater analysis of Organic Matter (OQD, BQD), nutrients concentration (Ammoniac Nitrogen, Total Phosphorus, Soluble Phosphorus...), Microbiological indicators (Coli sp) and parasites (eggs of Ascaris lumbricoides). Soil samples collected at the beginning and at the end of field work were analyzed relating to fertility and salinity. Due to high wastewater concentration of Ammoniac Nitrogen (53mg N-NH3/L), Total Phosphorus (7mg/l), Potassium (21mg/l), Calcium (36mg/l) and Magnesium (33mg/l), were added to soil about 387kg/ha of Nitrogen, 153kg/ha of Potassium, 51 kg/ha of Phosphorus, 263kg/ha of Calcium and 241 kg/ha of Magnesium during application , by 670mm irrigation table. Due to the nutrition potential wastewater influenced some physical fiber characteristics like length, Fineness (Micronaire Index) and CSP Count Strength Product presenting high reflectance index (78% average value) distinguishing cotton produced by what means inherent high quality according to International Textile Industry pattern. Production consequently was influenced by wastewater with cotton reaching high productivities and amount superior to 3300kg/ha of cotton seed corresponding to 1200kg/ha of cotton fiber, value above world average value (2001/2002) and performing within the five higher world productivities. Wastewater was able to substitute 180kg/ha application of Nitrogen fertilizers. Wastewater influenced soil environment from October/2002 to February/2003 and with regard to Potassium concentration increased 58% considering the average of all treatments using Nitrogen Fertilizers. Contrasting witnesses' wastewater increased for more then 100% available Sodium and regarding all average treatments fertilized with Nitrogen, it increased the soil Sodium in 79%. To other variables were not observed significant effects of wastewater use and from sanitation point of view was not possible to evaluate risks of pathogenic microorganisms' survival because soil had previous high contamination.