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Crop irrigation requirements are usually estimated based on crop evapotranspiration (ETc) as determined by the reference evapotranspiration (ETo) and crop coefficient (Kc). There is a lack of knowledge on the irrigation requirements of tropical forage crops in Brazil, contrasting with the increasing use of irrigation in pastures. The effort of this study was to investigate what would be the water needs of tropical forages in Southern Brazil, based on a robust experimental database. The study was carried out in São Paulo State-Brazil using different forages species and their combinations [Guinea grass (GG); Guinea grass + black oat + ryegrass (GOR); Bermuda grass (BG), and Bermuda + black oat + ryegrass (BOR)]. The experimental fields were fully irrigated, and the Kc values were derived from ETc measurements on lysimeters; ETo was estimated using daily data from a nearby weather station and the standard FAO56 parameterization. Mean daily ETc values for GG, GOR, BG and BOR were 4.1, 2.9, 3.6, and 3.4 mm, respectively, and respective mean Kc values were 0.99, 0.90, 1.0, and 0.94. Average Kc values for all plots decreased as ETo increased, producing a negative Kc-ETo relationship, mainly when ETo reached values greater than 5 mm d−1. This was most likely due to internal plant stomatal resistance to vapor release from the leaves diffusing to the atmosphere at high ETo. So, the time-based Kc curves described by FAO 56 manual should be adjusted for the analyzed crops considering different ranges of ETo to improve the required irrigation depth. [ABSTRACT FROM AUTHOR]

Reported benefits of green cane trash blanket (GCTB) on the production of sugarcane include soil water retention, supplement nutrients, regulating temperature, and carbon accumulation in the soil. However, it is still uncertain the extent to which the irrigated sugarcane growth is influenced by GCTB. Thus, this study was aimed to analyze a four-year (from 2013 to 2016) irrigated field experiments by a center pivot system in Brazil to evaluate the effect of the transition from burnt-to-GCTB in terms of evapotranspiration, detailed crop development, growth measurements, and soil temperature changes. The experiment consisted of two treatments (bare soil and GCTB) with detailed soil moisture measured by frequency domain reflectometry (FDR), evapotranspiration measured at field level by Bowen ratio method, and evaluations of crop growth and development over the growing seasons. The result showed that the GCTB did not affect crop growth and development except for a few measurement dates in one season which experienced a severe regional drought. In the other growing seasons, however, the study did not show difference in crop evapotranspiration, soil moisture, and crop growth variables. However, the GCTB reduced the soil temperature and its variability as compared to the bare soil treatment in all four depths monitored during the study, which resulted in an average decrease by 4.9 °C in the GCTB treatment in the 0–0.40 m depth profile. Although the GCTB treatment did not increase the yield and ETc, the GTCB in second ratoon (dry year) showed more stalk.m−2 than bare soil probably due to the lower temperature caused by the sugarcane residue on the soil surface. [ABSTRACT FROM AUTHOR]

Conflicts over water use and the high demand for food and biofuels have motivated the use of wastewater in irrigated agriculture. The study aimed to evaluate the nitrogen losses through nitrate leaching and nitrous oxide emission for sugarcane first ratoon irrigated by subsurface drip (SDI) with fresh water and treated domestic sewage (TDS) and traditional crop management under rainfed conditions. Therefore, the following treatments were implemented: T1—non-irrigated and topdressing fertilization; T2—irrigated with TDS, with fertigation; T3—irrigated with TDS, without fertigation; T4—irrigated with fresh water, with fertigation; T5—irrigated with fresh water, without fertigation. The nitrogen (N) fertilizer applied corresponded to 120 kg ha−1 to all treatments, with broadcast fertilization for nonirrigated cropping and, for the irrigated plots, it was performed by supplementing the concentration of the nutrients in the TDS and freshwater. All the fertigated treatments had lower leaching losses than nonirrigated treatment with topdressing fertilization, the total N loss for nonirrigated plots differed significantly from irrigated treatments, with a total loss of 16.36 kg N ha−1. The application of TDS by SDI to meet the needs for water and nutrients resulted in a decrease of N losses by NO3− leaching and N2O emissions, compared with traditional sugarcane cultivation under non-irrigated with topdressing fertilization (total of 16.36 kg ha−1 for T1), being the nitrate leaching the main factor that contributed to the N loss with a loss of 71% for T1 (11.50 kg ha−1). Irrigation with TDS, in addition to providing nutrients and water for sugarcane cultivation, can help minimize nitrogen contamination compared to conventional management methods through SDI systems. [ABSTRACT FROM AUTHOR]

Irrigation water requirements are commonly estimated based on the estimated crop evapotranspiration (ETc) as determined by the reference evapotranspiration (ETr) and crop coefficient (Kc). Recent studies show that, at high evaporative demand (high ETr), Kc tends to decrease, creating an inverse ETr-Kc relationship. The focus of this long-term study is to, if at high atmosphere demand, there is the same inverse ETr-Kc relationship in Nebraska, USA, one of the most intensely irrigated regions in the world, and as a result, propose an adjustment to the Kc–ETr approach. The study was carried out in eastern Nebraska for maize-soybean rotation fields for the period 2002–2012. The Kc was estimated based on energy balance data from eddy covariance flux towers installed in the field and a nearby automated weather station throughout the growing seasons. We found that average Kc values varied depending on the year under high ETr; measured ETc agreed reasonably well with the FAO-56 manual predicted values, but in years with high ETr such as 2012 and 2002 affecting ETc values over the growing season. It was observed that Kc decreased as ETr increased, mainly when ETr reaches values greater than 6 mm d−1 (P values < 0.001). This most likely was due to internal plant stomatal resistance to vapor release from the leaves diffusing to the atmosphere at high atmospheric demands. So, the time-based Kc curves described by FAO 56 manual should be adjusted for the analyzed crops considering different ranges of ETr to improve the required irrigation depth and irrigation management. [ABSTRACT FROM AUTHOR]

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Copyright of Revista Brasileira de Engenharia Agricola e Ambiental - Agriambi is the property of Revista Brasileira de Engenharia Agricola e Ambiental and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)