Conserving soil moisture in vegetables: Effects of weed management and cover crop mulches

During hot, dry summers like this, timely weed management and retention of surface mulch can help reduce crop stress and minimize irrigation costs.

Effects of weeds on soil moisture

Many weeds are voracious consumers of water. For example, large crabgrass and common lambsquarters use over 80 gallons of water to produce 1 lb of plant tissue. Evidence from our trials in asparagus suggests that such thirsty weeds may deplete soil moisture by as much as 0.5 inches per week in the heat of the summer. Under these conditions, timely removal of weeds reduces irrigation costs and improves crop yields.

Effects of cover crop mulch on soil moisture

Under reduced tillage systems, rye or wheat cover crops left on the soil surface can be very helpful for conserving soil moisture. For example, last week in our strip-tilled sweet corn trials, plots with rye residue on the soil surface had approximately 5 percent greater water content in the top 10 inches then plots without rye mulch (Table 1). This is equivalent to about 0.5 inches of irrigation savings.

Table 1. Effect of mulch on soil moisture
Effects of mulch on soil moisture

Weeds, mulch and winter squash

The combined effects of weeds and mulches have been very noticeable in our winter squash research trials this year (Photos 1-3). Where crabgrass is present, winter squash plants are wilting noticeably within two days of irrigation. In contrast, where weeds are effectively controlled with cultivation and herbicides, winter squash is relatively unstressed. The least stressed plants are those that were planted into a winter rye residue using a strip-till system.

Winter squash wilting Good winter squash Good winter squash
Photos 1-3. Winter squash on the left is wilting noticeably as a result of poor weed management. Plants on the right were grown with winter rye in a strip-tillage system. Good weed control combined with mulch can conserve up to 1 inch of water per week during warm summer periods.

For more information on the costs and benefits of strip-tillage systems for vegetables, contact the Dan Brainard at

Dr. Brainard’s work is funded in part by MSU’s AgBioResearch.

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