Effect of Deficit Irrigation on Nitrogen Uptake of Sunflower in the Low Desert Region of California

Effect of Different Tillage Practices on Sunflower (Helianthus annuus) Cultivation in a Crop Rotation System with Intercropping Triticosecale-Pisum sativum

The objective of this work was to investigate the effect of different soil tillage practices on sunflower cultivation in a rotation system with intercropping of Triticosecale-Pisum sativum. For this purpose, a two-year experimental field with a 5% slope was established in central Greece. There were four treatments with three replications each. The treatments were as follows: (a) no tillage planting parallel to the contour (NTC-PAC), (b) conventional tillage planting parallel to the contour (CTC-PAC), (c) no tillage planting perpendicular to the contour (NTC-PEC), and (d) conventional tillage planting perpendicular to the contour (CTC-PEC). During the experiment, the plant height, leaf area index, specific leaf area, plants' total nitrogen, and plants' proteins were measured. According to the results, the plant height ranged from 64.9 (CTC-PAC) to 85.2 cm (NTC-PEC) for the first year and between 66.5-86.5 cm in for the CTC-PAC and NTC-PEC treatments in the second year. Furthermore, the leaf area index (LAI) and specific leaf area (SLA), plants' total nitrogen and protein content and N-uptake were affected positively by the no tillage practice. To conclude, sunflower is a promising crop in a rotation system intercropping Triticosecale-Pisum sativum, cultivated under rainfed sloping conditions.

Modeling Approaches for Determining Dripline Depth and Irrigation Frequency of Subsurface Drip Irrigated Rice on Different Soil Textures

Water saving techniques such as drip irrigation are important for rice (Oriza sativa L.) production in some areas. Subsurface drip irrigation (SDI) is a promising alternative for intensive cropping since surface drip irrigation (DI) requires a higher degree of labor to allow the use of machinery. However, the semi-aquatic nature of rice plants and their shallow root system could pose some limitations. A major design issue when using SDI is to select the dripline depth to create appropriate root wetting patterns as well as to reduce water losses by deep drainage and evaporation. Soil texture can greatly affect soil water dynamics and, consequently, optimal dripline depth and irrigation frequency needs. Since water balance components as deep percolation are difficult to estimate under field conditions, soil water models as HYDRUS-2D can be used for this purpose. In the present study, we performed a field experiment using SDI for rice production with Onice variety. Simulations using HYDRUS-2D software successfully validated soil water distribution and, therefore, were used to predict soil water contents, deep drainage, and plant water extraction for two different dripline depths, three soil textures, and three irrigation frequencies. Results of the simulations show that dripline depth of 0.15 m combined with one or two daily irrigation events maximized water extraction and reduced percolation. Moreover, simulations with HYDRUS-2D could be useful to determine the most appropriate location of soil water probes to efficiently manage the SDI in rice.

Impact of Deficit Irrigation on Shallow Saline Groundwater Contribution and Sunflower Productivity in the Imperial Valley, California

Yield and production functions of sunflower (Helianthus annuus) were evaluated under full and deficit irrigation practices with the presence of shallow saline groundwater in a semi-arid region in the Imperial Valley of southern California, USA. A growing degree day (GDD) model was utilized to estimate the various growth stages and schedule irrigation events throughout the growing season. The crop was germinated and established using overhead irrigation prior to the use of a subsurface drip irrigation (SDI) system for the remainder of the growing season. Four irrigation treatments were implemented: full irrigation (100% full sunflower crop evapotranspiration, ETC), two reduced irrigation scenarios (95% ETC and 80% ETC), and a deficit irrigation scenario (65% ETC). The salinity of the irrigation water (EC) (Colorado River water) was nearly constant at 1.13 dS·m−1 during the growing season. The depth to groundwater and groundwater salinity (ECGW) were continuously monitored in five 3 m deep observation wells. Depth to groundwater fluctuated slightly under the full and reduced irrigation treatments, but drastically increased under deficit irrigation, particularly toward the end of the growing season. Estimates of ECGW ranged from 7.34 to 12.62 dS·m−1. The distribution of soil electrical conductivity (ECS) and soil matric potential were monitored within the active root zone (120 cm) at selected locations in each of the four treatments. By the end of the experiment, soil salinity (ECS) across soil depths ranged from 1.80 to 6.18 dS·m−1. The estimated groundwater contribution to crop evapotranspiration was 9.03 cm or approximately 16.3% of the ETC of the fully irrigated crop. The relative yields were 91.8%, 82.4%, and 83.5% for the reduced (95% and 80% ETC) and deficit (65% ETC) treatments, respectively, while the production function using applied irrigation water (IW) was: yield = 0.0188 × (IW)2 − 15.504 × IW + 4856.8. Yield reduction in response to water stress was attributed to a significant reduction in both seed weight and the number of seed produced resulting in overall average yields of 2048.9, 1879.9, 1688.1, and 1710.3 kg·ha−1 for the full, both reduced, and deficit treatments, respectively. The yield response factor, ky, was 0.63 with R2 = 0.745 and the irrigation water use efficiencies (IWUE) were 3.70, 3.57, 3.81, and 4.75 kg·ha−1·mm−1 for the full, reduced, and deficit treatments, respectively. Our results indicate that sunflowers can sustain the implemented 35% deficit irrigation with root water uptake from shallow groundwater in arid regions with a less than 20% reduction in yield.