Location: Water Management Research
2024 Annual Report
Objectives
Objective 1: Determine forage yield, water productivity and nutritional values of diversified forage systems under semi-arid conditions.
Objective 2: Determine effects of irrigation and cutting schedule on forage yield, crop water productivity, stand persistence, and nutritional values of alfalfa varieties.
Approach
For Objective 1: The hypothesis to be tested under this objective is that alfalfa summer irrigation cutoff and the use of annual forage crops result in improved forage nutritive value and water productivity compared to traditional alfalfa production practices. Field experiments with four treatments will be carried out over five years. A reduced-lignin alfalfa and winter and summer annual crops will be planted. The experimental design is a randomized complete block with four replications. Plots will be irrigated using a flood irrigation system with each treatment having a separate zone equipped with a valve and a flow meter to allow precise irrigation applications. Initially, all treatments will be irrigated to achieve stand establishment. Irrigation will be applied to match crop ET requirement and maintain soil moisture content in the one to three feet soil depth at 18-30% level. Reference ET from a nearby weather station will be used to determine crop ET by multiplying with crop coefficient values from different growth stages after cuttings. Forage yield, quality, water productivity, and yield-quality relationships of alfalfa and annual forage crops will be determined in relation to the different forage systems. If high heat stress events occur in the first year of alfalfa production and survival of alfalfa in the summer irrigation cutoff treatment is in question, we will provide supplemental irrigation to prevent plant stand loss.
For Objective 2: The hypothesis to be tested under this objective is that alfalfa forage yield is greater if cut every 35-days compared to 28-days under frequent sprinkler (FS) and simulated flood (SF) irrigations. Field experiments with FS and SF irrigation are planned for alfalfa varieties with reduced- and non-reduced lignin traits. The experimental design is a randomized complete block design with a split-plot arrangement with four replications. Irrigation/cutting schedule combinations and alfalfa varieties are main-plot and sub-plot treatments, respectively. The main-plot treatments are FS irrigation with a 35-day cutting schedule, FS irrigation with a 28-day cutting schedule, and one irrigation (SF) per harvest with a 28-day cutting schedule. Plots will be irrigated using an overhead sprinkler system. Each irrigation/cutting schedule treatment will be controlled separately using valves and water applied recorded with flowmeters. For FS treatments, irrigation will be applied weekly to match crop ET requirement. Similar reference ET and crop ET calculation approach and maintaining of soil moisture range and depths will be used as in Objective 1. Yield, quality, and plant biophysical parameters of alfalfa will be determined and analyzed to evaluate the interactive effect of irrigation frequency and varietal traits. If extreme weather events such as high heat stresses occur in treatment 3 that will lead to alfalfa stand loss, limited supplemental irrigation will be applied between harvests.
Progress Report
This report documents progress for project 2034-21500-001-000D, "Developing Diversified and Climate Resilient Forage Systems for the Western U.S.", which started December 2023 and continues research from project 2034-13210-002-000D, "Improved Management, Quality and Utilization of Alfalfa for Dairies in the Western U.S." For additional information, please see the expired project report.
In support of Objective 1, Field preparation is completed at the San Joaquin Valley Agricultural Sciences Center for planting alfalfa, winter pea and winter vetch in the fall and winter of 2024. The selected field site was deep tilled to 150 cm depth to break up hard pans for improved water infiltration and laser leveled to accommodate flood irrigation. Installation of field irrigation systems continues to deliver water to each treatment block as needed.
In support of Objective 2, Ongoing research involves investigations of alfalfa varieties for yield, quality, and water productivity responses to irrigation frequency (on a weekly and one irrigation per 28-day cut basis) according to cutting schedule (35-day and 28-day basis) treatments. Alfalfa plots were harvested three to five times depending on cutting schedules to determine yield per acre. Small plant samples from each plot were collected before each plot harvesting for forage quality determination. Soil moisture was measured before plot harvesting to monitor moisture dynamics. Plant biophysical properties were measured on a bi-weekly basis. Drone flight was conducted before each harvest for vegetation index and canopy temperature estimations.
Accomplishments
1. Precision alfalfa agriculture enhances yield and water use efficiency. Optimization of drip tape spacing, and installation depths could translate into management practice that increases alfalfa yield and water productivity. However, information on optimum drip spacing and depths and their impacts on soil profile wetting and alfalfa productivity is limited. ARS researchers in Parlier, California, in collaboration with University of California researchers, determined that out of the 15, 30, and 45 cm drip tape depths tested, drip tape installed at 45 cm depth was ideal allowing growers to provide additional irrigation without increasing topsoil soil water content closer to harvesting, which could result in higher yield and water use efficiency. This finding is valuable for alfalfa growers as a management tool to improve alfalfa yield and water productivity.