Water deficit at certain cotton growth stages can cause severe damage to crop development, affecting physiological processes and reducing reproductive structures, with consequent yield losses. The objective of this study was to evaluate the response of cotton cultivars under water deficit applied at different stages of the crop cycle. We compared the number of bolls per meter, cotton yield, and water use efficiency for eight different cotton cultivars under a water deficit of 15 days. We selected the following growth stages: Emergence (EM), First Square (FS), First Flower (FL), Peak Bloom (PB), and First Open Boll (FOB). The control treatment was irrigated with 100% ETc. The experiment was conducted in Apodi, RN State of Brazil, semiarid region, using a sprinkler irrigation system. The number of bolls per meter, cotton yield, and water use efficiency were influenced by the interaction of cultivars x deficit periods. Lowest values were observed for water suppression in the FL and PB stages. When the water deficit was imposed in the initial stages of growth (EM to FS) or after the FOB stage, the cotton yield reduction was not significant. At the same stage and water deficit, the behavior of the different cultivars was similar. Producers are urged to take this information into account when developing irrigation schemes for cotton crops, thereby avoiding water deficits during the most critical periods of the crop cycle.

Propôs-se, neste trabalho, avaliar a variabilidade espacial dos atributos de fertilidade do solo em Latossolo Vermelho Amarelo em plantio direto para o algodoeiro em Cristalina, GO, visando à adoção da agricultura de precisão no manejo da área. A grade amostral foi constituída de 90 pontos (80 x 80 m) distribuídos numa área de 57,6 ha. Foram determinados os teores de P, K, Ca, Mg, S, Na, Cu, Mn, B, Zn, Fe, matéria orgânica (MO), pH, soma de bases (SB), saturação por bases (V), saturação por alumínio (m) e condutividade elétrica aparente do solo (CE) a 30 e 90 cm de profundidade. Efetuou-se a análise descritiva clássica e em seguida foram modelados semivariogramas para todos os atributos e mapas de krigagens. A dependência espacial das propriedades do solo analisadas indica que as variações espaciais devem ser consideradas no planejamento de coleta de amostras de solo e nas práticas de manejo do solo. Para a adoção da agricultura de precisão e aplicação de insumos em taxa variável, deve-se realizar um estudo criterioso da variabilidade da fertilidade do solo, gerando mapas por classe de fertilidade de cada atributo, o que permite identificar para quais atributos esta prática de manejo deve ser adotada.

The objective of this study was to evaluate the effect of irrigation depths on seed cotton yield and water-use efficiency of cotton cultivars in the Brazilian semi-arid region. Field experiment was conducted during two consecutive years in the Apodi region, RN, using sprinkler irrigation. The experiment consisted of factorial combination in split-plots, composed of four irrigation depths (130; 100; 70 and 40% ETc and four cotton cultivars - FiberMax 993, BRS 286, BRS 336 and BRS 335), in randomized block design with 4 replicates. Data were evaluated by mean test (Tukey) and regression analysis. Considering the irrigation depths of 40% ETc, cotton yield was 48% lower compared to the higher irrigation depth (130% ETc). The higher water-use efficiency (0.69 kg m^-3) was obtained with 70% ETc irrigation depth. The highest seed cotton yield was achieved with the higher water depth for all evaluated cultivars. Yield response factor (Ky) was equal to 0.632, 0.711, 0.784 and 0.858, for FiberMax 993, BRS 286, BRS 335 and BRS 336 cultivars, respectively. FiberMax 993 and BRS 286 cultivars presented the best performance, showing that they are more suitable for irrigated farming in the semi-arid region.

The objective of this research was to investigate the effects of irrigation with treated wastewater and nitrogen (N) fertilization on the chemical characteristics of a Haplustalf soil cultivated with cotton. An experiment was conducted in a greenhouse in a completely randomized design with four replicates, and arranged in a 5 x 4 factorial. Five doses of N fertilization (0, 45, 90, 135 and 180 kg ha^-1) and four sources of irrigation water (freshwater, wastewater treated by an anaerobic reactor, wastewater treated by an anaerobic reactor and post-treated by intermittent sand filter in series, wastewater treated in a septic tank and post-treated by an intermittent sand filter) were tested. Irrigation was daily performed from July 2011 to January 2012 according to the water demand of cotton resulting in a water depth of 620 mm. It was found that, compared with the conventional management with freshwater irrigation, treated wastewater provides greater accumulation of micronutrient, potassium and sodium in the soil, increasing the risk of sodification in irrigated areas.

O algodoeiro é uma das culturas mais importantes em valor econômico no grupo das fibras, por seu volume e valor de produção. Este trabalho foi desenvolvido com o objetivo de caracterizar um descaroçador quanto às qualidades física e fisiológica das sementes e tecnológica da fibra de algodão. O descaroçador foi construído com os seguintes componentes: limpador, cilindro de serras, cilindro de escovas, condensador e um motor elétrico trifásico de 3 CV para acionamento dos dispositivos de beneficiamento. O delineamento foi o inteiramente casualizado em esquema fatorial (2 x 2 x 2 x 4), de duas cultivares de algodão (BRS 187 8H e BRS Safira), dois tipos de serra (11 ¾" e 12"), dois processos de limpeza (com e sem limpador) e quatro rotações (500, 550, 600 e 650 rpm) com quatro repetições. Durante o beneficiamento das sementes os tipos de serra e os processos de limpeza não interferiram na qualidade física e fisiológica das sementes; já nas características tecnológicas da fibra o descaroçador foi eficiente com a rotação de 550 rpm utilizando-se serras de 12" e dispositivo de limpeza ativado (limpador).

Most studies about soil organic carbon stock changes in the Cerrado (Brazilian Savanna) biome are either related to field data collected in clayey Ferralsols or different land uses, as if they were in equilibrium. This study aimed to evaluate the effect of tillage systems and crop sequences on the soil organic carbon stock and crop yield, in a sandy Ferralsol from Bahia, Brazil. The experimental design was randomized blocks, with four replicates. Soil samples were collected after fve years of cotton, soybean and maize monocropping under heavy disk harrow and leveling harrow (conventional tillage), and of crop rotation of cotton, soybean and maize with green manure or cover crop (no-tillage). Additional samples were collected from a non-cultivated site (Neotropical Savanna, Cerrado sensu stricto). Soil conservation practices such as no-tillage and crop rotation with cover crop and green manure favored the soil organic carbon stock at the 0-40 cm layer, with the highest values reaching 36.03 Mg ha−1. The accrued soil carbon stock under conventional tillage and monoculture of cotton, maize and soybean was lower than under no-tillage, which ranged from 30.9 to 54.9 %, with the soil organic carbon stock increasing at the annual rate of 2.36 Mg ha−1 during fve years. The no-tillage, with the soybean-maize-cotton rotation, in combination with cover crop and green manure, increased the cotton and soybean yields, with a simultaneous organic carbon accumulation in the sandy soil.