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Limited Water Resources Discourage the Adoption of Cover Cropping Almonds Furrows


For this month's blog post I will be covering some unique barriers to adoption for winter cover crops in Almond production for the southern parts of the Central Valley, known as the San Joaquin Valley. First, I would like to explain a little about my fellowship with Grizzly Corps and Sustainable Conservation. My role within Sustainable Conservation has been to research and understand soil health practices’ potential impact on water resources as well as some of the systemic issues that are hindering adoption of those practices in the San Joaquin Valley and Central Coast of California. This work is supported by peer-reviewed literature and interviews with farmers, technical assistance providers, academics, and other stakeholders in California agriculture.



In my exploration into soil health’s effect on water resources in California, cover crops have dominated the conversation. Within the soil health discussion, cover crops tend to offer some of the most benefits, despite presenting significant barriers to adoption. Research shows the beneficial effect of winter cover crops on both water quality and quantity. Cover crops have the potential to become an important tool for increasing California’s resiliency to water and climate-related threats. I am hoping to shed some light on a few barriers to adoption that are unique to the southern San Joaquin Valley almond orchards.





Benefits:

When examining scientific literature specific to California and stakeholder interviews, cover crops have excelled in their potential to affect water resources. Below is a quick list of how cover crops can benefit water resources. Please note, this is not the full extent of benefits that can result from the use of cover crops.

Cover crops can affect:

• Water quality

o Reduces nitrate leaching into groundwater through nitrogen scavenging

o Reduces surface runoff and preserving topsoil

• Water quantity

o Increases the supply of water

▪ Improves the soil’s infiltration rates affecting the overall likelihood of on-farm groundwater recharge

o Decreases the demand for water

▪ Improves a soil’s water holding capacity, the amount of water stored in the root zone of the soil

• Soil Organic Carbon & Microbial Biomass

o Adds a food source by providing labile (readily decomposable) carbon inputs o The presence of living roots provides habitat and symbiotic relationships with microbial communities


[For citations, please feel free to reach out to me at Edgrant@berkeley.edu]


Many researchers, organizations and agencies have done a great job of showing cover crops’ potential benefits. I would like to focus on some region-specific barriers that growers might face when adopting cover crops.


Water Supply Barriers:

Despite all of these benefits, cover crops face a mighty barrier in the southern regions of the Central Valley: limited water supplies. Cover crops, like every other plant, require water. And cover crops have been shown to lower soil water levels, at least in the short run. So, when growers are faced with water cutbacks from either droughts or regulatory restrictions (like the Sustainable Groundwater Management Act), it is hard to make a case for a practice that could infringe on their water allocations. This issue is especially relevant for almond growers in the southern San Joaquin Valley, where annual precipitation is around 10 inches per year and growers are very reliant on groundwater or delivered water. It is important to unpack these barriers to fully comprehend the long-term, net effect of cover crops on water supply.


Wet Years Versus Dry Years:

Understanding how much cover crops will deplete soil water levels is a tricky metric to predict. A cover crop's net effect on water quantity may depend on the amount of winter rain fall in a given year. During wet years, cover crops can catch large volumes of surface flows from floods or torrential downpours, recharging aquifers and preventing runoff. Therefore, cover crops in wet years could improve the relative groundwater levels. A cover crop's roots can improve the soil’s infiltration capabilities, by creating pour space & breaking up large soil aggregates. Their addition of organic matter to the soil also helps stabilize soil aggregates, which can increase the soil water holding capacity of a field. All of these water-related benefits from cover crops could significantly improve a field’s resiliency to future droughts and water cutbacks. Wet years provide enough precipitation to grow a healthy winter cover crop, resulting in benefits to water supplies.


In dry years where there isn't enough rain to germinate, or grow a healthy cover crop, the cover crop may look to existing soil water to meet their water demand. This would lower a field’s short-run water levels. It is hard to tell if this soil water depletion would hurt a farmer’s water rations, because cover crops water usage is relatively low compared to the prominent tree crops in the San Joaquin Valley. A southern San Joaquin Valley UC researcher explained to me that a winter cover crop’s water usage compared to an almond orchard is about 1 acre-inch, compared to 52 acre-inches of water. That is about 2% of the annual water requirement of an almond orchard. Although 2% of the normal irrigation requirement for almonds seems negligible, if you are considering promoting wide adoption of winter cover crops, 1 acre-inch scaled up to an entire region is significant. For these southern regions, the water supply constraints could significantly limit the benefits that cover crops could provide.

Irrigation Systems:

If a grower didn’t want to risk the investment of a cover crop on winter rainfall, then one might look to use an early irrigation to germinate the cover crop. However, operational constraints arise when considering how to get the cover crops started. The trend with orchard irrigation systems in the San Joaquin Valley is moving away from flood irrigation and towards micro-sprinklers and double-line drip irrigation system. The USDA’s NRCS considers double-line drip the BMP, or “Best Management Practice,”

as they can meet a tree’s water demand with significantly less water applied. Overall, this trend is beneficial to reducing on-farm water demand, however it does leave the orchard furrows dry, which creates the issue of trying to start and irrigate a winter cover crop. Given the double-line drip trend, a grower looking to irrigate a cover crop in-between furrows would have to install a temporary irrigation system. This would increase the financial burden of cover cropping on the grower as well as potentially jeopardize their water rations in drought years, by tapping into their farm’s irrigation allocation. It seems unlikely for growers to change their irrigation system in order to accommodate water for cover crops.


Framing Water Constraints as a Cost:

These considerations point to a farming tradition that is as old as farming itself: trying to predict the rain. Southern growers would not see any benefit from investing in cover crops if there is little-to-no rainfall in a drought year. A technical service provider interpreted this issue, describing it simply as a higher cost of cover cropping for a southern San Joaquin Valley grower compared to Northen Central Valley growers due to the risk of a low rainfall.


Their logic was that:

If a grower in the southern San Joaquin Valley seeds a cover crop every year, for 10 years, and only has 6 years of sufficient rainfall for a proper cover crop, then they're paying for 10 years of cover crops but only getting the benefits in those 6 years, when it was wet enough to grow the crop. Compared to the Sacramento Valley which has much more annual precipitation, a grower might get 10 years of good rains, and sees 10 years of the cover crops benefit.


The classic Cost-Benefit analysis shows that the net benefits of cover cropping across multiple years is lower in southern regions than northern ones, therefore represented as a higher cost to the grower. In my experience, growers tend to be very cost oriented. Framing a cover crop’s benefits and barriers as an economic cost or economic savings, can be an effective tool for grower adoption.


Conclusively, there are numerous benefits to cover crops, many of which that benefit the broader environment rather than solely the grower. Cover crops can be a very valuable tool for farmers combating some of Califorina’s changing climate. For San Joaquin Valley almond growers, a cover crop can improve their long-term resilience to droughts, however, if not careful, a cover crop could add some sunken costs to the grower, and potentially exacerbate their lack of irrigation water. Luckily, there is a team of UC Davis researchers investigating the net effect of cover crops on water supply for almond production (Stay tuned!). It will be crucial to understand the economic, operational, and resource constraints that impact growers in order to successfully scale the adoption of cover crops and broader soil health practices within California Agriculture.


Thanks for reading! As mentioned above, if you have any questions, comments, concerns or just want to see some research, please email me at Edgrant@berkeley.edu


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