Fertigation technology has evolved considerably over the past 20 years, often in concert with improvements in drip and micro spray irrigation technology.

It is now common practice to deliver soluble fertilizers and or fluid fertilizer products through drip or micro spray systems in a variety of agricultural venues.

“Fertigation” is defined as “the application of soluble fertilizers to crops via dissolution in irrigation water and transport via the irrigation water to the effective root zone of the crop of interest”.

Many shorter terms are used to describe fertigation: “Intermittent Liquid Feed,” “Constant Liquid Feed,” “Intensive Fertigation Programs,” “Open Hydroponics,” and many others.

The management programs, which govern the frequency of application, the concentration of nutrient element or elements applied and the placement of these nutrients relative to the effective root zone are varied.

This article examines a useful approach to fertigation management, where the concentration of nutrient element or elements applied in the fertilized irrigation water is precisely controlled. This approach is referred to as “Proportional to Flow Fertigation.”

The goal is to control and manage the concentration of nutrient element or elements present in the soil water (water which occupies a portion of the pore space). This fertigation management strategy is truly “spoon feeding” the crop.

Proportional to Flow Fertigation is characterized by the following features:

• One major principal of this type of fertigation is to supply the lowest possible concentration of nutrient element sufficient to maintain normal leaf mineral nutrient concentrations in the leaf tissue.

• A second important principal is that all water applied to the crop during a fertilized irrigation event is uniformly dosed with the desired nutrient element concentration (ppm). Irrigation Distribution Uniformity (DU) should be high. Soluble fertilizers, dissolved in the irrigation water will move as the water moves, and go where the water goes. Deep percolation should be avoided. Fertilized water should be accurately applied to the effective root zone only.

• Nutrient element concentrations are controlled by the Proportional to Flow Fertigation system automatically with variation in water flow rate. The operator has management capability over the nutrient element concentrations, present in his irrigation water.

• Frequency of application is high, often at each irrigation. This is indeed, truly “spoon feeding.”

• Laboratory measurement of nutrient element concentrations in the fertilized line water is a routine practice to insure proper functioning of the system.

• Multiple nutrient elements, N, P, K as well as magnesium, sulfur and micro elements can be simultaneously applied, if required. Appropriate system design allows simultaneous injection of an array of nutrient elements. Potential chemical incompatibility is avoided by correct management of nutrient element concentrations.

Concentration is defined as parts per million (ppm). Many growers prefer to calculate amounts of nutrient or fertilizer applied as pounds per acre or units per acre. Parts per million (ppm) is a useful measure of concentration in irrigation water. Consider 1.0 ppm nitrogen (as element) per 1.0 acre foot of water = 2.71 pounds of nitrogen (as element). Parts per million are merely a weight relationship between the weight of the nutrient element applied and the weight of the water in which the nutrient is dissolved.

There is an important distinction between concentration and amount of fertilizer. Concentration refers to the nutrient element concentration, expressed in parts per million, in the fertilized irrigation water. Amount of nutrient or by extension, amount of fertilizer refers to the pounds or units of fertilizer applied per volume of fertilized irrigation water applied (or more commonly, per acre). This approach employs quite low concentrations of nutrient elements, dissolved in the irrigation water. Typically, no flushing of irrigation lines is required, due to the fact that fertilizer concentrations are quite low.