During the past weeks I have received several emails asking for advice on fall nutrient application and I decided to put all those recommendations together in this article. It is well known that temperate fruit crops (including fruit trees, grapevines, and berry crops) use reserves to support the initial vegetative growth and fruit set in the spring until the new growth shifts from being a sink to a source of carbohydrates (this happen about 3-4 weeks after bud break). This period between initial spring growth and the beginning of fruit development is critical to secure high yields of quality fruit, and it relies almost exclusively on the reserves from the previous year. Then the question is what can we do to increase reserves to have a successful beginning of the season next year? Fall nutrient application seems like an opportunity to boost reserves, however many research studies have had mixed results when fall nutrients were applied, probably because effectiveness of these applications will depend on many other factors such as tree health and nutritional status, soil nutrient levels, cropping levels, etc. Here are some general recommendations for fall nutrient application.

Micronutrient deficiency in tissue and soil test results. If tissue/foliar test results show low levels of Born and Zinc, which are both critical micronutrient for fruit set and shoot development, a fall application can help overcome this deficiency before the following spring. This application can be done to the foliage or to the soil, with the caveat that low soil temperatures in the fall will decreased the rate of nutrient uptake and that foliar application have to be done before leaves fall. Zinc and Boron become less available for the plants when soil pH is above 7, so correction to soil pH can be sufficient to correct deficiencies if the soil levels of these nutrients are in the normal range but the tissues test shows deficiencies.

Nitrogen (N) deficiency and overcropped trees/vines/bushes. During the fall, plants move N from the leaves, where it forms part of the chlorophyll molecule responsible for photosynthesis as well as amino acids in proteins and nucleic acids among others, to the limbs, trunks, and roots to store it for next year. This reserve nitrogen is key for the new spring growth and early fruit development, because it is easily accessible to the plant compared to soil N that will not be available until the soil warms up in mid to late spring. Research on fall N application to fruit crops has shown that there is a positive response in terms of yield and growth if the plants are deficient or marginally low in N, usually this would appear in the results of the tissue analysis but growers might also evaluate end of the year shoot growth and overall vigor as an indicator of N needs. For this reason, I would only recommend a fall N application if the trees show low tissue levels and/or if the trees were overcropped, which will result in low reserves. In terms of N application rates for the fall, I would not go over 5-10% of the total N that you usually apply during the growing season.

Macronutrients (Ca, Mg, K, P). There is limited research on the effect of fall application for these nutrients. Anecdotally, we have applied Epson salts (a common fertilizer containing Magnesium-Mg) to cold hardy grapevines in our research vineyards at West Madison Ag Research Station with good results. However, this was done to correct a deficiency and not as regular application in the vineyard’s nutrient management plan. I have been asked by some apples growers if fall would be a good time to apply Calcium (Ca), specially in orchards that struggle with high incidence of bitter pit. Uptake of Ca from the soil happens at the root tip level, meaning that during periods of active root growth is when most of Ca is taken up from the soil, and although periods of root growth are not as predictable as aboveground phenology, new root growth is expected to happen during the growing season. Root growth in fruit trees, grapevines, and berry crops can happen during the fall, but this might not necessary happen every year. In terms of foliar Ca application during the fall, it could be possible that Ca is translocated inside the plant into buds, limbs, and trunks, making it available during the spring. However, there isn’t much research on this topic to support a recommendation of foliar or soil Ca application during fall.

In summary, fall nutrient application whether is foliar or soil application should be considered if there is a deficiency, the plants show low vigor, and/or have been overcropped. Fall application of Zinc and Boron could be beneficial to increase fruit set and early fruit development if tissue test levels are in the low range. Currently, there is not enough research on the effect of fall fertilization for macro nutrients Ca, Mg, and K; growers should continue applications of these nutrients during the growing season.

This article was posted in Apples, Berries, Grapes and tagged Amaya Atucha, fall nutrient application, foliar nutrient, macronutrients, micronutrient, micronutrient deficiency, Nitrogen, nitrogen deficiency, Nutrient management, overcropped.