Supressão da irrigação na cultura do algodão: impactos no crescimento, produtividade e qualidade da fibra.

Abstract

Taking into consideration the importance social and economic to the cotton culture to the Northeast of Brazil, where there is th second biggest textile plant of Brazil, and with a lack of a suitable handling to irrigation in most of th region, the following research has been carried on. Five single seasons for irrigation were considered to 20(T1), 30(T2), 40(T3), 50(T4) and 60(T5) some day after the first herbacious cotton flower appeared (Gossypium hirsutum L. r. Latifolium Hutch), cultivate CNPA-7H, about the culture up coming, growing/development of the aereal part and technology of the fiber. The experimental rowing in spread blocks has been used, concerning to five treatments and four repetitions. The last irrigation times T l , T2, T3, T4 and T5 provided results on branch cotton in the order of 2013, 3092, 3199, 2720 and 2893 Kg/ha, having a total blade application of irrigation of 492.3, 601.9, 678.0, 759.3 and 831.9 mm, respectively, without remarkable difference between the treatments, however the T3 obtained about 37% bigger than the T l . The function of the obtained production for the raw cotton is given throuch the expression: R = -8730,9 + 33,91 L - 0,0242 L2 . In a general way the growing rates of culture havenit bee affected by irrigation supression, however the plants receiving a more adequatd layer of water obtained a better performance, mainly about the treatment T3, irrigation supression to 40 DAPF, in which the plants grew 106,4cm over the usual size. The leaf area behavior has been similar to the plant size. The treatments 3, 4 and 5 reached the best results, meaning that the hidric stress advanced the leaves' thriving. The equations that best explain the LAI variation of treatments 1, 2, 3, 4 and 5 respectively are: LAI = -0,0021EAD2 + 0,3344EAD - 6,7273; LAI = -0,0021 EAD2 + 0,3413EAD - 6,9068; ; LAI = -0,0025EAD2 + 0,4472EAD - 9,7005; LAI = -0,0024EAD2 + 0,4295EAD - 9,692 e LAI = -0,0015EAD2 + 0,2982EAD - 6,361. The treated plants had bigger hydric dephicit, presented opening percentage of sprouting bigger than the others. To 106 EAD, 85% of sprouting on treatment 1 were open, whereas for treatments 4 and 5 the percentage taks 43,7 and 52,5% respectively, showing that th hydric stress has provided the sprouing opening in advance. The irrigation cut, during managed periods, didn't cause remarkable effects on technological variety of checked fiber, the rates getting the trade classification parameters, according to features to be cultivation CNPA-7H heracious cotton plant, comes to be 76 EAD, with na irrigation layer around 602mm.