With most 2023 crops out of the field or orchard and as attention turns to planning for 2024, soil health should be high on growers’ postharvest to-do list. But with about every year-round agronomic decision, make sure you’re timing any soil health-focused input so it’s cost-effective and sets up every acre for success next year.

In many ways, that means completely different management strategies for annual and perennial crops. But there are two areas on which growers should focus after harvest, according to Grow West Technical Service Manager Layne Wade.

“Generally, you want to prioritize soil minerals and biology in making sure you’re setting things up well for 2024,” Wade said. “Compost or humic acids help get carbon out there to feed microbes and increase biological life in the soil. The fall postharvest period is also a good time to apply minerals like potassium to row crop acres because it doesn’t leach as much as other minerals. That’s the mineral we see applied most often in the fall after harvest, including in orchard crops.”

Adding a soil inoculant like those offered by leading biologicals manufacturer Prime Dirt can help make those postharvest applications more efficient by improving nutrient cycling, enhancing soil structure and increasing root production. Specific to inputs like humic acid, Prime Dirt products include ingredients that facilitate more efficient microbial breakdown of organic and inorganic matter in the soil — namely nutrients and minerals — to more effectively feed both annual and perennial plant roots in the soil biome. This translates to more efficient plant uptake and equips plants to better weather environmental stressors like drought.

Different strategies for annual versus perennial crops

Wade recommends thinking differently about each nutrient you’re considering applying to annual row crop acres in the fall based on its characteristics, namely how long it takes to first oxidize in the soil, then how long it remains plant-available into the 2024 growing season. Nitrogen, for example, oxidizes quickly, is highly water-soluble and binds weakly to soil particles, so it’s more prone to leach out of the root zone. Potassium, on the other hand, is a cation that binds more tightly to soil, so it is more likely to remain in the area it is applied, maintaining availability for future root uptake. Potassium can also be applied via buried drip irrigation systems, making its application an easy addition to your postharvest to-do list.

“Effective fall soil amendment and fertilizer applications are a balancing act of managing cost, plant uptake, regulations and how nutrients move in the soil once applied,” Wade said. “Don’t automatically assume you need to apply everything in one fall application. The most cost-effective postharvest strategy accounts for optimal application volume in the right time window.”

Here’s where postharvest soil and crop health application similarities between annual and perennial crops end. Normally, once nutrients are balanced in annual crop acres, they’re fairly well set up for the following year, with a few exceptions for pre-plant nutrient applications to optimize soil conditions. But postharvest soil health management on perennial acres requires attention to key times in plant or tree nutrient uptake to set up the crop for success in the following year.

Why permanent crop root flushes mean so much to effective fall applications

It’s all about root flushes, the biannual events when perennials like tree crops and vines experience a period of root growth, and this is a time when nutrient uptake can be maximized. For mature grapevines it normally happens first just before or during bloom, then secondarily it occurs again after harvest. For bearing tree crops such as almonds and walnuts, the initial seasonal root flush occurs around one month or so after flowering in addition to the postharvest secondary root flush. That makes postharvest applications an efficient time for targeting soil and root health, according to Wade, who said he “spends time with a shovel each season to decide when root flush is happening with perennials.”

“Roots of bearing perennial crops aren’t constantly producing new ‘flushes,’ they alternate growth habits with leaves and crop development. With the crop harvested, roots start flushing and growing since a majority of the energy in those trees and vines can go down into the roots. With this flush of growth, the roots are more absorptive and they expand to pick up carbohydrates and available nutrients from the soil for the dormant season,” Wade said. “The efficacy of postharvest applications is impacted a great deal by how well you time them with your perennial crop root flushes. You’re more likely to have what you apply make it to those roots and into the plants when you match their applications with root flushes.”

The cost benefit of well-timed fall applications

Timing applications around root flushes may be a different strategy to many, Wade admits. But it’s a way to get precise with postharvest applications, often using existing drip or sprinkler irrigation systems to apply some nutrients, biologicals and soil amendments. It also helps growers get more bang for their fertilizer buck and set up their perennial crops for a quick start the following spring.

“You can do things the way you always have because it’s inexpensive and what you’re used to doing, but your plants may not be absorbing what you apply,” Wade said. “We’re going to be in a much better place with perennial crops if we’re targeting those times when roots are better able to absorb the nutrients you apply.”

The best way to confirm when your perennial crop roots are flushing is conduct root digs and look for any changes in root size and condition. Doing so will help ensure fall applications are effective, whether they’re minerals, nutrients or biologicals like Prime Dirt soil inoculants. Talk to your Grow West PCA to find out where your crops stand today.