To guarantee that an alfalfa crop has adequate soil moisture during the hot season growers should start monitoring soil moisture well before summer begins.
A challenge with using drip irrigation in alfalfa fields is to keep soil moisture levels stable during the typically hot and dry months. Planning and keeping track of deep moisture requirements during the summer can help growers reap profits from yield increases.
Dennis Hannaford of Netafim says, “It’s critical to minimize moisture stress. Once a grower gets a little behind, they have less ability to catch up.”
It’s a plant physiology issue which short circuits a plant’s ability to recover, Hannaford says.
“When it gets hot and humid, the plant essentially shuts down and it tends to not bring up enough moisture to protect itself.”
The end result is the plant closes cells and doesn’t transpire.
Going into summer, growers need to address moisture stress and make sure the deep moisture in the soil profile is adequate. Hannaford says deep moisture carries the crop from one curing event to another.
“It’s vital to protect the deep moisture which is what the crop pulls from when we do cuts,” he says.
After soil moisture is safeguarded, other stresses can compromise yield and quality. Growers should scout for pests, including gophers, and take appropriate steps as needed. Plants can also be stressed by nutrient deficiencies which can plant growth. A tissue sampling program can help ensure the crop’s productivity.
The ‘Irrigated Alfalfa Management for Mediterranean and Desert Zones’ book published in 2008 by the University of California (UC) Alfalfa Workgroup includes a chapter on irrigating alfalfa in arid regions. It was written by UC’s Irrigation Specialist Blaine Hanson, plus UC Cooperative Extension Farm Advisors Khaled Bali at Imperial County and Blake Sanden at Kern County.
The specialists say water used by crops (evapotranspiration or ET) is a two-part system of transpiration and evaporation. The first refers to the water taken up by the plant that evaporates from the leaves and the latter represents moisture which evaporates from the soil.
The ET process is affected by the type of crop, climatic conditions, plant health, the stage of growth, salinity, soil moisture content, and other factors. High temperatures and sunlight stimulate ET and following alfalfa harvest there’s much more evaporation occurring in flood irrigation due to a greater amount of soil exposed to the sun.
Less soil is exposed as the crop grows and the canopy fills. ET switches to more transpiration. This is a critical period to monitor against soil moisture deficiencies, which can negatively impact the ET process and affect yields.
Sub-surface drip irrigation minimizes soil surface wetting and therefore minimizes the evaporation component of ET.
According to the book’s authors, “Seasonal alfalfa yield is directly related to seasonal ET. Alfalfa yield increases as ET increases with maximum yield occurring at maximum seasonal ET (determined by climatic conditions). Insufficient soil moisture, the result of insufficient applied water, is usually the reason that ET is less than maximum which results in reduced yield.”
Russ Schafer understands the importance of monitoring alfalfa’s soil moisture during dry conditions. He previously managed alfalfa acreage at a farm in Buttonwillow, Calif. with a Netafim subsurface drip system.
“If the plants looked stressed, we were already too late,” he said as cautionary advice.
With field-to-field variables, Schafer used a number of tools to make decisions – a UC ET chart, moisture probes which checked deep moisture between three and five feet in depth, plus digging down five to 10 inches to get a deeper soil sample to check the moisture levels throughout the profile, and then watered accordingly.
He said it’s important to not just rely on the ET chart to correctly determine a field’s moisture.
Schafer found that irrigating with drip gave him the extra control he needed to manage soil moisture during hot summer months while maintaining the crop’s needs right up to cutting.
“With subsurface drip, you can irrigate close to harvest and get a more uniform crop,” he said.