SUSTAINABLE POTATO CROPPING SYSTEMS FOR IRRIGATED AGRICULTURE IN THE PACIFIC NORTHWEST
Location: Vegetable and Forage Crops Production Research
Title: Setpoints for Potato Irrigation using Real-time Continuous Monitoring of Soil Water Content
Submitted to: Journal of Crop Improvement
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 11, 2007
Publication Date: June 1, 2008
Citation: Alva, A.K. 2008. Set points for potato irrigation using real-time continuous monitoring of soil water content in soil profile. J. Crop Improvement. 21:117-137.
Interpretive Summary: Potato is very sensitive to adequate availability of water during most of the growing period. However, application of excess water should be avoided in order to minimize leaching of water and nutrients below the rootzone. Irrigation decisions are generally made based on either crop or soil monitoring. Real-time, continuous monitoring of soil water content within the rooting depth provides a basis to determine when and how much to irrigate to overcome water deficits. Likewise, simultaneous monitoring of water content below the rootzone soil provides a basis to judge leaching of water below the rootzone. Capacitance probes were used to monitor soil water content at 10, 30, 60, 90, and 120 cm depth in Ranger Russet potato fields irrigated by center pivot. Plants were irrigated to replensih full evapotranspiration (ET) or 70% of ET. The latter constitutes deficit irrigation. Using the soil water monitoring data, we developed the following irrigation guidelines: (i) full point: maximum amount of water that can be held in the rooting depth soil, i.e. equivalent to 72 mm in the top 60 cm; (ii) refill point: the allowable soil water content below which causes serious negative effects on growth and quality of tubers, i.e. equivalent to 54 mm water in the top 60 cm depth soil; (iii) driest point: the lowest water content which cannot be extracted by the plants, i.e. equivalent to wilting point or 18 mm in the top 60 cm depth soil. Thus, for optimal production of high quality potatoes, the soil water content in the top 60 cm depth soil should be maintained between 54 and 72 mm water. Application of water in excess of 72 mm will result in leaching of water and nutrients below the rootzone. Deficit irrigation below 54 mm water in the top 60 cm depth soil will results in serious negative affects on the crop growth, production and quality of tubers. For the field studies, it is necessary to validate the above irrigation setpoints.
Adequate availability of water during the potato growing season is critical for production of high yields of premium processing quality tubers. Real-time, continuous monitoring of soil water content in the soil profile can be used to develop irrigation setpoints to ensure adequate availability of water in the rootzone and minimize excess water application which can be leached below the rootzone. In this study, capacitance probes were used for automated measurement of soil water content at 10, 30, 60, 90, and 120 cm depth in a Center Pivot irrigated potato (cv. Ranger Russet) field in a Quincy fine sand (mixed, mesic, Xeric Torripsamments). Depth integrated soil water content was calculated in the soil profile to which represents the rooting depth (0-60 cm) and below the rooting depth (60-120 cm). Irrigation was scheduled to replenish either full evapotranspiration (ET), or 70% of ET (deficit irrigation). The soil water content at the 10 and 30 cm depth, as well as depth integrated soil water content in the 0-60 cm depth soil responded to each irrigation event. The “Full Point” and “Refill Point” for the soil within potato rootzone (0-60 cm depth) were estimated to represent the maximum water holding capacity (without leaching below), and the soil water content at which irrigation is to be scheduled to avoid soil water stress, respectively. Depth integrated soil water content in the 0-60 cm depth soil profile remained mostly above the Full Point during most of the growing season in the Full ET irrigation treatment, but remained within the Full Point and Refill Point for the deficit irrigation treatment. The tuber yield for the latter treatment was lower by 24% as compared to that for the former treatment. Thus, further research is necessary to reevaluate the irrigation setpoints to facilitate optimal irrigation to minimize water leaching below the rootzone and ensure no negative effects on the tuber yield and quality.