you determine what mixes are most appropriate for your operation and water use goals. There is evidence to suggest that planting cover crops increases water use efficiency and water availability. Cover crops add organic matter to the soil. Organic matter is excellent at holding water; it works like a sponge that traps and retains water. • Organic matter holds 18–20 times its weight in water (USDA NRCS 2013). One can expect the PAm Seed Mixes to provide about 3.5 tons of organic matter per acre. • There are 1,000,000 tons of soil in a 6-inch-deep acre plot, so growing a cover crop to about waist high will provide 0.03%–0.05% of organic matter every year. Just 1% organic matter in the top six inches holds up to 27,000 gallons of water! (USDA NRCS 2013). Organic matter helps water stay where it’s needed most, around the root systems of crops. But cover crops also use water, so let’s take a closer look at how much water cover crops use in an orchard system. How Much Water do Cover Crops Use? Cover crops grown in the fall and winter months will need less water due to shorter days and cooler temperatures. More research needs to be done to determine how much water cover crops use from October to March. Typically, this is the time of the year when Seeds for Bees cover crops are growing. However, there is still something to be learned from a 1989 cover crop study that took place in an almond orchard from April to August. The results were published in California Agriculture in an article titled, “Orchard water use and soil characteristics,” by Prichard, et al. The results are shown in Table 2 (below). Resident vegetation (weeds), clover, bromegrass, and herbicide (bare ground) were the four treatments that were compared in two orchards: a newly planted one (Orchard A) and a mature one with
70% soil shading (Orchard B). The herbicide (bare ground) treatment used the least amount of water. Bromegrass used from 4% less to 18% more water than bare ground. Clover used more than bromegrass, 14% to 29% more than bare ground, and the most water was used by weedy resident vegetation, from 17% to 36% more than bare ground. A clover cover crop used less water than resident weeds! If something is growing on the orchard floor, it might as well be a cover crop. It will use less water than the weeds while increasing the soil’s water-holding capacity.
Table 2. Seasonal water use in treatments at orchards A and B (Prichard 1989)
The 2021–2022 Seeds for Bees open enrollment period is happening now. Interested growers are encouraged to apply at ProjectApism.org/Seeds-For-Bees. We are currently accepting applications through November 15th, or until we run out of seed. Growers of all types can apply and first year applicants are awarded up to $2,000 of free seed. Don’t forget – early planting is key to getting the most benefit as possible from your cover crop stand. Sign up today! Feel free to contact me, Billy Synk, at Billy@ProjectApism.org for any questions regarding the Seeds for Bees program, cover crops, habitat, or bees/pollination.
References: Shroder, Shulamit and Kanter, Jessie (2021) Cover Cropping to Achieve Management Goals. Lessons Learned from Cover Crop Trials in the San Joaquin Valley.
July 15, 2021. Progressive Crop Consultant. USDA NRCS (2013) Soil Health Key Points Prichard L., Terry (1989) Orchard water sue and soil characteristics. California Agriculture. July-August: 23-25
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