Ask Your PCA

Ask Your PCA: When do I apply soil amendments?

Issue Date: Oct 13 2021
Justin Nay PCA, Integral Ag Services Durham, California.

Early fall is all about soil amendments and fertilizers for almond growers. Soil samples are collected during the summer and evaluated for deficiencies that need to be addressed. The common ones are calcium, gypsum or lime. Potassium or sulfate of potash is used to build up the soil if needed. Tiger or elemental sulfur is applied if there is a pH problem.

Compost use has been increasing over the last 10 years because growers have seen it improves soil structure. Growers broadcast compost in the fall—2 to 4 tons per acre. Compost releases small amounts of nutrients over time, and it provides better water holding capacity. Organic orchards still apply more compost than conventional, but there are more growers talking about compost and asking for it.

All these amendments require rainfall to irrigate them into the soil, and a big concern for growers is timing these amendments with a fall pre-emergent application for weed control. If a fall pre-emergent is applied on top of compost or gypsum, it could get tied up and not work as effectively, which makes timing of these applications critical.

But timing can be tricky, particularly in a dry fall. While a pre-emergent can be irrigated into the soil, it's only about 70% as effective compared to half an inch of rain a week or two after application.

Growers try to spread the amendments first, and hopefully a couple of rain events follow so they will settle it. A pre-emergent application would follow in November. If the amendments are delivered late, or applied late, then a decision has to be made of which to do first. The bottom line: Pre-emergent takes priority because managing weeds later is too difficult.

Amendments, depending on rainfall, can be applied until bloom in February. Most growers try to finish by early December, but that depends on the weather.

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