Water management is becoming more challenging with increases in both very dry and very wet years — often back-to-back. This dry-wet-dry “weather whiplash” can be especially challenging to manage in perennial crops like nuts and wine grapes. One emerging strategy and philosophy for coping with weather whiplash is regenerative agriculture.
Regenerative agriculture is both a core set of management principles and a strategy to “stack” several practices together that align with these principles. These principles include the following:
Multiple practices can align with these principles and adoption of practices should be tailored to specific climates and cropping systems.
We are part of a team of scientists working on a $10 million U.S. Department of Agriculture Coordinated Agricultural Project titled “Sustaining Groundwater and Irrigated Agriculture in the Southwestern United States Under a Changing Climate” investigating how regenerative agricultural practices can help irrigated semi-arid agricultural systems adapt to weather whiplash. Regenerative ‘stacked’ practices were chosen for this project that make sense for these climates and systems, including cover cropping (see fig. 1), reduced tillage/traffic (see fig. 2), livestock integration (see fig. 3), and organic amendment addition (see fig. 4). To better understand how these stacked practices might help water management in semi-arid systems, we look to soil structure.
Soils have both fixed and changeable properties which are important for hydrologic functions. For example, soil texture (sand/silt/clay content) cannot be changed with management. However, soil structural properties or how soil particles are arranged can change with management. These soil structural properties include bulk density (dry soil weight/volume), aggregate stability (how well soils resist breakdown), infiltration (initial downward movement of water into soil), available water holding capacity (total amount of water in soils accessible by roots), and hydraulic conductivity (how easy it is for water to move through pores at a given water content). Together, these properties make up the physical health of the soil. A soil with strong physical health has many different types of functional pores, like an excellent sponge. It can infiltrate intense precipitation events, capture and store water, have enough oxygen for roots and microorganisms and drain water to recharge aquifers. Soils with robust physical health make the most of applied irrigation and precipitation for both the current and future growing seasons. A soil with strong physical health is a desired outcome of effectively incorporating regenerative agricultural practices.
However, it is important to point out that understanding the impacts of even a single practice, like cover cropping (see fig. 1), on soil physical properties can be complex and vary based on soil texture, climate and choice of cover crop. Generally, cover crops improve infiltration and drainage to their rooting depth through the creation of additional pore space by root systems. Over many years of practice, cover crops can potentially add organic matter to the soil and alter additional soil physical properties. In semi-arid fruit and nut systems, cover crops usually provide these physical benefits to the orchard or vineyard “floor” where they are most densely planted between rows of trees or vines. In this way, they are an investment in water futures by helping to infiltrate winter precipitation and potentially recharge aquifers.
Tillage is a tricky practice as it can increase infiltration and reduce bulk density in shallow layers (to tillage depth) in the short term but compact soils at deeper layers over the long term. Tillage can also weaken soil structure and lead to greater soil erosion (see fig. 5). Reduced tillage techniques such as no-tillage and alternative tillage (every other row tilled in a given year) can decrease soil bulk density and increase infiltration at deeper soil depths over the long term. From a water management standpoint, functional deep soils can help perennial systems both withstand droughts (imagine deep roots being able to penetrate and access water) and also promote recharge in wet years (imagine water moving through deep soil layers to the aquifers below). Similarly, livestock incorporation can help with cover crop management through grazing and alter the organic matter content of soils over time through the incorporation of manure and urine. Though their impacts to nutrient pools have been well studied, we are trying to better understand livestock impacts to soil physical health when stacked with reduced/no-tillage, cover cropping and other organic amendment additions.
The interactions of the practices when stacked are challenging to study and tease apart, but our team hypothesizes that they will be synergistic to promote greater soil physical health than each alone.
Some preliminary results from our field studies demonstrate enhancements in soil structure. Full adoption of regenerative agricultural practices (cover cropping, no-tillage, animal grazing and organic amendment addition) yielded better soil stability in the surface soil layer (top 4 inches) and lower soil bulk density at depths of 4-16 inches below the soil surface, compared to a management strategy that adopted only a single or no regenerative agricultural practices. Water infiltration rates varied across practices adopted and soil textures (medium vs. fine), but it demonstrated greater positive change in medium-textured soil only after a minimum of three years of practice adoption. Change in the soil’s physical environment is slow and can take at least five years before noticeable changes are seen.
None of these practices are without nuanced management challenges. It is important to start slowly and monitor the impacts of regenerative practices on system hydrology. Some suggestions would be to soil test, especially for changes in soil structure (bulk density, infiltration) or indicators of such changes (organic matter content) over time to see if the practices are having the intended outcomes for drought and flood resilience. An additional suggestion would be to monitor soil moisture in areas where regenerative practices were incorporated to observe how the system responds to rain events, holds water and drains water. After careful monitoring of soil moisture and structural changes over time, the next step is to start altering irrigation management (rate, magnitude, frequency) to potentially account for improvements in soil physical health.
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