By Forrest Scharf, P. Ag., Provincial Specialist, Fruit Crops, Regina
Fruit growers often struggle to determine how much fertilizer to apply, when applications should be made, the right types of fertilizers to use and what delivery model is best to ensure efficient nutrient absorption. Answering these questions and employing recommendations, will bring growers in-line with 4R nutrient stewardship principles promoted by Fertilizer Canada.
For fruit growers, adhering to nutrient stewardship principles can be more challenging than it is for most conventional crop producers. Many of the species in the fruit sector are perennials, as opposed to annual crops like oilseeds, cereals and pulses. There are a wide variety of rooting characteristics, as well as genetic differences that impact fertilizer requirements. In addition, the nutritional needs change over the course of the season, as well as through the years as perennial plants mature.
A good example of how crop needs change as plants grow is found in Strawberry production. Based on soil and foliar tests, recommendations may indicate a need for a broad spectrum fertilizer application that includes high percentages of macronutrients (N-P-K and S) and micronutrients (Fe, Mb, Zn, B, Mn, Mg, Mo and Ca). Examples of products commonly used by strawberry growers include Plant-Prod Solutions Complete and Plant-Prod Solutions Total Plus.
A simple response to the soil or foliar analysis may suggest a large quantity of product needs to be applied. Unfortunately, the shallow rooted strawberry plants don’t need as much access to nutrients in early Spring as they do when the plants have grown and are setting significant amounts of fruit. This is especially true for new plantings that lack a significant number of leaves and have a somewhat slow growth progression. Complicating matters further are soil texture, mineral content, pH, and other factors that influence nutrient availability. In high pH soil conditions micronutrients are more likely to become limited. Often high pH soils have relatively high nutrient content and relatively greater clay content when compared to low pH soils.
High pH soils may require foliar application of micronutrients (Fe, Zn, B) in order to make them available to plants. Low pH soils that have a greater percentage of sand and less intrinsic fertility, they require greater amounts of macronutrients, but typically don’t retain them as long. So applications may have to be small in spring, and increase towards harvest. In addition; for shallow rooted crops like strawberries, especially in sandy textured soils, the frequency of fertilizer application which is often done via irrigation, has to be relatively high due to lack of retention in the upper soil profile. Deeper rooted crops and plants growing in heavier textured soils with high organic matter content, would generally require fewer applications.
Another complicating factor is that the application of too much of one particular nutrient may influence the availability of another nutrient, especially for tree fruits that stay in place for long periods. If a deficiency or excess of a particular nutrient exists, it may cause lack of plant availability for other nutrients. The Ontario Ministry of Agriculture, Food, and Rural Affairs has a good resource to help growers wade through these complications.