Resumen Este estudio evaluó la contribución de la nutrición con potasio (K) y la aplicación de las láminas de las aguas residuales al rendimiento agronómico del algodón colorido. Los tratamientos consistieron en cinco láminas de riego (50, 75, 100, 125 y 150% de la evapotranspiración del cultivo - ETC) y cinco dosis de K (0, 50, 100, 150 y 200% de la recomendación del cultivo). Fue también utilizado un control absoluto de riego con lámina 100% de la ETC y fertilizado con una recomendación de 100% N-P-K. Así como los tratamientos el control también tuvo cuatro repeticiones. La altura de la planta, el diámetro del tallo, el área de la hoja y la acumulación de materia seca del algodón en los brotes se evaluaron a los 130 días después de la emergencia (DAE), mientras que el peso del algodón semilla, se evaluó a 135 DAE. Los resultados indican que el uso de aguas residuales domésticas tratadas para compensación del 100% de ETC promueve un mayor aumento de peso y crecimiento del algodón colorido sin la necesidad de fertilización con K, lo que evidencia el potencial de las aguas residuales para el algodón colorido para una agricultura sostenible.

Abstract This study evaluated the contribution of potassium (K) nutrition and application of wastewater depths to the agronomic performance of colored cotton. Treatments consisted of five irrigation depths (50, 75, 100, 125 and 150% of crop evapotranspiration - ETC) and five K doses (0, 50, 100, 150 and 200% of the recommendation for the crop) and an absolute control irrigated with 100% ETC water depth and fertilized with 100% N-P-K recommendation. Each treatment and the control had four replicates. Plant height, stem diameter, leaf area and shoot dry matter accumulation of cotton were evaluated at 130 days after emergence (DAE), whereas seed cotton weight was evaluated at 135 DAE. Our findings indicate that the use of treated domestic sewage for 100% ETC replacement promotes greater gains of weight and growth in colored cotton without the need for K fertilization, evidencing the potential of wastewater for colored cotton for sustainable agriculture.

ABSTRACT The Mossoró-Assu-Baraúna district, Rio Grande do Norte State (RN), is recognized by the intense production of horticulture, mainly muskmelon for export. However, this region is often devastated by intense droughts. Thus, the muskmelon production is predominantly under irrigated condition and, due to constant threat of water resources collapse on the region, a rigorous irrigation water management in the region is needed. The main objective of this article was to analyze the seasonal pattern of energy balance partitioning and evapotranspiration on irrigated muskmelon crop on the region around Mossoró-RN. The study was carried out in two areas of commercial production of muskmelons in the Mossoró-Assu-Barúna district, during two growth seasons from 2012-Jun to 2012-Nov. The components of energy balance and evapotranspiration were determined by using the Bowen Ratio Energy Balance method. It was observed that more than 60% of the net radiation (Rn) was converted into latent heat flux (λE), while 21 and 11% of Rn was converted into sensible heat flux (H) and soil heat flux (G), respectively. The ratio λE/Rn varies according to the change of leaf area index (LAI) while the ratios H/Rn and G/Rn vary inversely with the LAI. The agreement λE/Rn and LAI is also evidenced by similarity between curves of crop evapotranspiration (ETc) and LAI, particularly when the melon crop reaches its maximum vegetative growth (LAI > 3). The muskmelon ETc ranged from 265 to 289 mm, values that are similar to those found by other researcher.

RESUMO: Objetivou-se avaliar a produtividade, o rendimento e a qualidade de fibras de cultivares de algodoeiro herbáceo submetidas a diferentes lâminas de irrigação. Durante dois anos consecutivos foi conduzido um experimento de campo na região de Apodi (RN) disposto em parcelas subdivididas com quatro lâminas de irrigação (130, 100, 70 e 40% da evapotranspiração da cultura - ETc) e quatro cultivares de algodoeiro (FiberMax 993, BRS 286, BRS 336 e BRS 335), em delineamento de blocos casualizados com quatro repetições. Foram avaliadas a produtividade, a percentagem e a qualidade das fibras do algodoeiro. Houve diferença significativa para as características avaliadas entre as cultivares e as lâminas de irrigação. A rega com déficit (70 e 40% ETc) ocasionou declínio na produtividade de algodão em caroço, na percentagem e qualidade das fibras. As cultivares FiberMax 993 e BRS 286 apresentaram as maiores produtividades e percentagem de fibras entre as cultivares avaliadas. Com a lâmina de 40% da ETc as cultivares de fibra média (FiberMax 993, BRS 286 e BRS 335) apresentaram fibras curtas, e a cultivar de fibra longa (BRS 336) apresentou fibra média. De forma geral, a redução na qualidade da fibra não foi severa, haja vista a fibra produzida está dentro da faixa de qualidade aceitável pela indústria têxtil nacional, mesmo em condições de déficit hídrico. Dessa forma, a decisão em irrigar o algodoeiro com ou sem déficit hídrico dependerá dos custos da irrigação e do valor de mercado do produto.

ABSTRACT: This study was conducted to evaluate seed cotton yield, fiber yield, and fiber quality traits of cotton cultivars grown under different irrigation levels in Brazil. The experiment was conducted over two years in the region of Apodi - RN, with sprinkler irrigation. Treatments comprised of 4 irrigation levels i.e., 130, 100, 70 and 40 % of the crop evapotranspiration (ETc) and 4 cotton cultivars i.e., FiberMax 993, BRS 286, BRS 336 and BRS 335. The experimental design was factorial with randomized complete block design and four replicates. Yield, lint percent and fiber quality traits determined were evaluated. Different responses were observed for cultivars at various irrigation levels. Cultivars grown under limited irrigation exhibited a decline in the seed cotton yield, lint percent, and fiber quality. Cultivars with the highest yield and lint percent were FiberMax 993 and BRS 286. Within irrigation level of 40 % ETc, the medium fiber cultivars produced short fibers whereas the long fiber cultivar, BRS 336, produced medium fiber length. Overall, the different levels of water deficits did not significantly affect fiber quality of the four cultivars tested as all fiber quality traits remained acceptable for the domestic textile industry.

The main objectives of this study were documenting how energy balance partitioning and ET vary seasonally along each growth season of cotton crop under full irrigation conditions in the Brazilian semiarid. The studied area was located in the Apodi Plateau, which is located on west of Rio Grande do Norte state and is an area with extensive agricultural suitability and semiarid climate. Micrometeorological measurements were taken during cotton growth season on dry seasons of 2008 and 2009 years in a cotton crop field of about 5 ha, and the energy balance components were derived from Bowen Ratio Energy Balance (BREB) method. The obtained results revealed important role of the vegetative growth of cotton crop in the energy balance partitioning. The values of LE/Rn ranged from 58% (Initial growth season) to 81% (Middle-growth season) in 2008 and from 63% (Initial) to 81% (Middle season) in 2009. These variations is in accordance to LAI variations, which ranged from 0.14 cm2 cm–2 (Initial growth season in 2008) and 0.18 cm2 cm–2 (Initial growth season in 2009) to about 5.0 cm2 cm–2 (middle season). On the other hand, H/Rn and G/Rn varied inversely with the LAI variations. The concordance between LE/Rn and LAI is evidenced by similarity between curves of ET and LAI and between curves of Kc and LAI, especially when LAI reaches values greater than 3.0.

Medições de umidade do solo em campo são complicadas. Assim, técnicas de sensoriamento remoto são necessárias, pois permitem o mapeamento da umidade do solo, em escala de campo e regional, na profundidade média da zona radicular da vegetação existente. O objetivo deste estudo foi avaliar a precisão de uma relação empírica para obter a umidade do solo a partir de dados de sensoriamento remoto para as condições irrigadas nos solos da Chapada do Apodi, no semiárido brasileiro. A relação empírica já foi testada para as condições irrigadas em algumas regiões do planeta como México, Egito e Paquistão, apresentando resultados promissores. Essa relação foi avaliada a partir de dados coletados em um experimento em campo de algodão. A campanha experimental foi realizada em uma área de 5 ha com algodão irrigado. Foram medidos os componentes do balanço de energia e a fração evaporativa (Λ), utilizando o método da razão de Bowen. Coletaram-se, ainda, dados de umidade do solo (θ) usando uma sonda de perfil PR2 (Delta-T Devices Ltd). A relação empírica foi testada utilizando os valores de Λ e θ experimentalmente coletados e foi aplicada usando os valores de Λ obtidos a partir do algoritmo SEBAL e três imagens TM - Landsat 5. Há forte correlação entre os valores medidos e estimados de θ (p<0,05) e R² = 0,84; não houve diferenças significativas em nível de p<0,01, segundo o teste de Student. De acordo com as análises estatísticas, a relação empírica pode ser aplicada para estimar a umidade do solo na zona radicular sobre condições irrigadas, ou seja, para fração evaporativa maior que 0,45.

Field-based soil moisture measurements are cumbersome. Thus, remote sensing techniques are needed because allows field and landscape-scale mapping of soil moisture depth-averaged through the root zone of existing vegetation. The objective of the study was to evaluate the accuracy of an empirical relationship to calculate soil moisture from remote sensing data of irrigated soils of the Apodi Plateau, in the Brazilian semiarid region. The empirical relationship had previously been tested for irrigated soils in Mexico, Egypt, and Pakistan, with promising results. In this study, the relationship was evaluated from experimental data collected from a cotton field. The experiment was carried out in an area of 5 ha with irrigated cotton. The energy balance and evaporative fraction (Λ) were measured by the Bowen ratio method. Soil moisture (θ) data were collected using a PR2 - Profile Probe (Delta-T Devices Ltd). The empirical relationship was tested using experimentally collected Λ and θ values and was applied using the Λ values obtained from the Surface Energy Balance Algorithm for Land (SEBAL) and three TM - Landsat 5 images. There was a close correlation between measured and estimated θ values (p<0.05, R² = 0.84) and there were no significant differences according to the Student t-test (p<0.01). The statistical analyses showed that the empirical relationship can be applied to estimate the root-zone soil moisture of irrigated soils, i.e. when the evaporative fraction is greater than 0.45.

Um requisito fundamental para adoção de manejo da irrigação é a determinação diária da evapotranspiração (ET) das culturas. Em caráter operacional o método do coeficiente de cultura proposto pela Food Agriculture Organization (FAO), através do seu relatório 56 (Irrigation and Drainage Paper), é largamente utilizado na determinação da ET, e tem apresentado precisões que o tornam mundialmente aceito. A ET com base no coeficiente de cultura (Kc), obtido a partir de índices de vegetação, particularmente o NDVI, tem sido calculada em vários estudos e para diversas culturas alcançando muita precisão, quando comparado com observações de campo. Diante do exposto, este trabalho teve por objetivo calcular a ET diária e sazonal da cultura do algodoeiro utilizando o método do Kc dual obtido em função do Índice de Vegetação por Diferença Normalizada - NDVI, obtido a partir de imagens TM - Landsat 5 livre da presença de nuvens. Os resultados revelaram precisões bastante confiáveis, pois foram verificadas diferenças menores que 10%, quando comparados com valores da ET obtidos pela técnica da Bowen, corroborando com o desempenho alcançado pelo método em outras pesquisas realizadas em outras regiões do planeta. Dessa forma, pode-se concluir que o método apresenta bastante confiabilidade e simplicidade.

A fundamental requirement for adoption of irrigation management is to determine the crop daily evapotranspiration (ET). On an operational basis the crop coefficient method proposed by the Food and Agriculture Organization (FAO) through its report 56 (Irrigation and Drainage Paper) is widely used in the determination of ET and due to its accurate estimative, it has been globally accepted. The ET-based crop coefficient (Kc) obtained from vegetation indices, particularly the Vegetation Index Normalized Difference (NDVI) has been measured in several studies and various crops showing great accuracy when compared to field observations. The objective of this study was to calculate the daily and seasonal ET of cotton crop using the method of dual Kc obtained as a function of the NDVI obtained from TM - Landsat 5 images clouds free. The obtained results are reliable, because less than 10% differences were found when comparing to the Bowen ratio technique observations, corroborating to the method performance achieved in other experiments conducted in other regions of the Earth. Thus, one can conclude that the method both simple and reliable.

Objetivou-se estudar, num solo aluvial, franco siltoso, no vale do Açu, no Rio Grande do Norte, o efeito do momento da última irrigação e da população de plantas sobre a altura das plantas e a produtividade do algodoeiro herbáceo (Gossypium hirsutum L.r. latifolium Hutch), cultivar Acala del cerro. Os tratamentos foram definidos pelos momentos da última irrigação aos 65, 80, 95 e 110 dias após a emergência e pela população com 30.000, 60.000, 90.000 e 120.000 plantas/ha. Usou-se o delineamento experimental em blocos ao acaso, com parcelas subdivididas, e quatro repetições. A altura das plantas aumentou com o retardamento da última irrigação e com o tamanho das populações. Houve efeito (P <= 0,01) positivo da interação entre os momentos da última irrigação e o tamanho das populações, sobre a produtividade da cultura. O melhor resultado, 4.090 kg/ha de algodão em rama, foi proveniente da última irrigação processada aos 95 dias com a população de 90.000 plantas/ha. Últimas irrigações aos 65 e 80 dias foram consideradas como cedo demais, e aos 110 dias, como muito tardias para a produtividade da cultura.

In an alluvial soil, silt loam, of Açu valley, in the state of Rio Grande do Norte, Brazil, a research was carried out to study the effect of time of the last irrigation and plant population on yield and plant height of the herbaceous cotton (Gossypium hirsutum L.r. latifolium Hutch) cultivar Acala del cerro. Treatments consisted of times of the last irrigation at 65, 80, 95 and 110 days after emergence and populations with 30,000, 60,000, 90,000 and 120,000 plants/ha. The experimental plan was a randomized complete blocks in a split-plot design, with four replications. Delaying time of last irrigation increased height and plant populations. A significant effect (P <= 0.01) of interaction between time of last irrigation and plant population was found for cotton yield. The highest cotton yield (4,090 kg/ha) was obtained with the interaction between time of last irrigation at 95 days and in population of 90,000 plants/ha. Irrigation times at 65 and 80 days were considered too early, and at 110 days too late for cotton yields.