Key Objective – Building Soil Biology
Tuesday, March 14, 2017
Last week I was walking vineyards above the Alexander Valley near Geyserville, where they’ve received an overabundance of rain this winter, with a customer. As much of the vineyard remained saturated, our conversation turned to what happens to nutrients that have been exposed to long periods of wet conditions and how we might approach getting his vines on track this spring.
Ideal soil has about 50 percent solid matter, 25 percent water, and 25 percent air. Soil that has been wet for long periods of time loses air in the pore spaces and becomes compacted. Plants have difficulty growing in soils without adequate pore spaces because plant roots require oxygen in the soil as well as moisture. A key point regarding saturated soils is that they lose many of the beneficial bacteria and other organisms that promote healthy plant growth. Mycorrhizal fungi, for example, often have trouble establishing themselves in saturated soils.
Given the wet winter overall that we experienced in the West, growers should want to make sure their soil biology is active and thriving. This needs to be a long-term objective regardless of the year, but this year there is likely a greater need to replace lost beneficial bacteria to help plants more efficiently uptake nutrients. Every nutrient that’s available to a plant needs the intervention of a third party (bacteria) to alter its form so it can be absorbed by the plant. The only nutrient that doesn’t fall into this category is nitrogen. Our compost teas, like Metagrow ST, provide both intensive and a wide variety of microbes capable of replenishing soil biology. Seaweed extracts, like Aquasap, can also help promote root growth early in the season, which is critical for generating early plant growth and leaf development. I have a feeling that we may be playing catch-up in many regions this season and getting a good start will be essential. Early leaf growth (plant solar panels) is important as the photosynthetic rate increases until leaves attain full size (approximately 40 days after unfolding) and decreases steadily thereafter (Pratt, C., and B.G. Coombe. “Shoot growth and anthesis in Vitis.” Vitis 17: 125-133 (1978))
Speaking of nitrogen, it’s the nutrient most likely to leach out of the soil. When there is a large amount of precipitation in a short time, nitrogen is flushed out of the top soil layers into deeper layers that plant roots cannot reach. Continuous small amounts of precipitation will do the same thing but at slightly slower rate. We prefer to utilize products with nitrogen that don’t promote too much vigor in a short period of time. Pacific Gro, for example, is cold processed fish hydrolysate that has nitrogen and a considerable amount of chitin making calcium, in a very available form, accessible to the plant. Agrostim, our comprehensive structured fertilizer, provides an organic source of nitrogen that can be applied through the drip or as a foliar. Sea-Crop, a seawater mineral concentrate containing an abundance of elements and minerals, acts as a catalytic trigger that drives nutrient and organic matter cycling.
Cool wet conditions promote fungal growth, and this year will be especially challenging. A grower shared a story with me about the time he was granted the contingent land used by a dairy farmer to expand growing of his melons. The melons that were grown conventionally on his land had severe downy mildew, while the melons growing on the new dairy farm land had zero mildew. The active soil biology on the dairy farm land hadn’t been destroyed by past farming practices, and it provided the plant with the proper soil biology to thrive and defend itself. So building soil biology is being proactive! We also offer an organic listed systemic fungicide called Thyme Guard.