Journal of Irrigation and Drainage Engineering

Agro-hydrological models are considered an economic and simple tool for quantifying crop water requirements. In the last two decades, agro-hydrological physically based models have been developed to simulate mass and energy exchange processes in the soil-plant-atmosphere system. Although very reliable, because of the high number of required variables, simplified models have been proposed to quantify crop water consumes. The main aim of this paper is to propose an amendment of the Food and Agricultural Organization (FAO) of the United Nations FAO-56 spreadsheet program to introduce a more realistic shape of the stress function, valid for mature olive orchards (Olea europaea L.). The modified model is successively validated by means of the comparison between measured and simulated soil water contents and actual transpiration fluxes. These outputs are finally compared with those obtained with the original version of the model. Experiments also allowed assessing the ability of simulated crop water stress coefficients to explain the actual water stress conditions evaluated on the basis of measured relative transpirations and midday stem water potentials. The results show that the modified model significantly improves the estimation of actual crop transpiration fluxes and soil water contents under soil water deficit conditions, according to the RMSEs associated with the revised model, resulting in significantly higher than the corresponding values obtained with the original version.

Cover cropping techniques are efficient for reducing pollutant leaching, avoiding soil erosion, or enhancing soil properties of agricultural soils. However, few studies evaluate the overall effect of cover crop (CC) on agricultural ecosystem functioning, and it is necessary to ensure that advantages of CC are not compensated by potential negative effects such as soil salinization. To improve the understanding of these complex processes, the authors analyzed water, nitrogen, and salinity dynamics in a maize cropping system with CC (vetch, barley, and fallow treatment), which was introduced in the intercropping season using both an experimental and modeling approach. As compared with a control treatment, the CC reduced nitrate leaching (64% for the barley treatment and 29% for the vetch treatment) without increasing soil salinity. In addition, the CC reduced the top layer salinity when maize was sown. Although the CC reduced with respect to fallow the net salt losses, in these conditions, excessive irrigation to favor salt leaching was not needed and, therefore, deep-water contamination risk with nitrate was reduced.

The variable and limited availability of water for irrigation in agriculture is a general challenge for farmers to cope with. Sophisticated irrigation strategies are needed that allow an efficient management of the available water resources, i.e., ensuring high water productivity (WP). Controlled deficit irrigation (DI) can be such a strategy in which soil-water status specific thresholds (in either soil-water tension or moisture) are used to trigger irrigation. For DI systems to be effective, irrigation control is of utmost importance, yet thresholds are likely to be chosen by trial and error. Hence, systematic investigations for deriving reliable thresholds are needed that account for different DI strategies. In this study a methodology is presented for evaluating the performance of sensor-based DI systems for very high soil-water tension threshold values. The study consists of three parts: a DI experiment with maize was carried out where a new sensor was employed that allowed measurement of high soil-water tensions and that was used to control irrigation. From that experiment, a crop growth model was calibrated, and finally the model was used in a simulation study to systematically investigate parameters for implementing effective setups of DI systems with high soil-water tension thresholds. Possibilities and limitation of this methodology are shown and discussed when applied for investigating and evaluating the potentials of sensor-based DI systems.

The goal of this study was to define procedures needed to make a Standardized Reference Evapotranspiration (${\mathrm{ET}}_{os}$) zone map using daily climate data from full stations, having solar radiation, air temperature, wind speed, relative humidity, and from partial stations, having only temperature data. For partial stations, the ${\mathrm{ET}}_{os}$ was estimated either by substitution of data from nearby full stations or by using a calibration factor and the Hargreaves–Samani equation estimate of reference evapotranspiration. The substitution method gave statistically better estimates of ${\mathrm{ET}}_{os}$ than the calibration method. In addition, to improve the number and distribution of ${\mathrm{ET}}_{os}$ estimates, three interpolation techniques were evaluated. Ordinary kriging provided better spatialization of ${\mathrm{ET}}_{os}$ data than the inverse distance weighting and radial basis function.

The objective of this work was to evaluate the effects of subsurface drip irrigation (SDI) and sugarcane spacing on stem yields, sugarcane technological quality, and the theoretical recoverable sugar yields during four cycles of sugarcane cultivation. The experimental field was set up in randomized blocks treated with three planting row spaces (1.5 m, 1.8 m, and a double row planting scheme with $1.3\times 0.5\mathrm{m}$ between the planting rows) and subdivided into fertigated and nonirrigated sections. The following parameters were analyzed: percentage of soluble solids contained in the juice (brix), percentage of apparent sucrose in the juice (Pol), total recoverable sugar (TRS), stem yield, and the theoretical recoverable sugar yield. The data were evaluated using analyses of variance, and mean values were compared using Duncan’s test with significance accepted at the 5% probability level. The results showed that irrigation increased stem yields in the ratoon cane cycles and that the theoretical recoverable sugar yields increased in the last two ratoon cane cycles. In general, the sugarcane’s yield characteristics were not altered by irrigation except during the second ratoon when the Brix, Pol, and TRS values were higher than those in the rainfed areas. Regarding the row spacings, double row planting produced the greatest stem yields and theoretical recoverable yields in the plant cane cycle and the second ratoon cane cycle. No interactions between irrigation and row spacing on stem production or yield characteristics were observed, but an interaction was observed for the theoretical recoverable sugar yield in the second sugarcane ratoon cycle. These results illustrate the benefits to sugarcane properties of SDI over the four years of this research.