We currently do not recommend SuperCal SO4 for fertigation since is it is only crushed to 70% passing 100 mesh, so we cannot guarantee that it will pass though all irrigation openings. With that said we are aware of some farmers that are doing this practice and we have received a number of phone calls from other farmers interested in this process this year.
Fertigation with gypsum
Applying fertilizers such as gypsum through a center pivot irrigation system affords many benefits to the crop, soil and grower. It is required that the fertilizer being used is fully soluble and/or will stay in suspension during the irrigation process. Mixtures of gypsum and water may have to be agitated for up to an hour to assure that the gypsum is fully solubilized and is in suspension. Continued agitation through the irrigation process is recommended.
The practical challenges of injecting gypsum relate to plugging up the system. The most immediate incidence of gypsum plugging occurs either when more gypsum is injected than can be dissolved into the irrigation stream or when not enough time is allowed between the injection of the slurry and its arrival at the system filter. In either case undissolved gypsum coats the filter and plugs it. This can be overcome by reducing the concentration rate of the injection and, when possible, by moving the injection point farther upstream from the filter.
Perhaps the most common plugging problem associated with gypsum injections is lime scale formation. Lime scale (calcium carbonate) is formed when calcium ions (either naturally present in the source water or added as calcium sulfate in gypsum) combine with naturally occurring bicarbonates in the water.
Water quality is also important in maintaining the solubility of the fertilizers. When we dissolve gypsum into water that contains appreciable (100 mg/L or greater) amounts of bicarbonates and has a pH of 7.0 or greater, we are setting up a system to actively precipitate calcium carbonate (lime scale). When dealing with waters with high potential for lime scale formation (high total alkalinity), it may be more cost effective to seek methods of applying calcium to the vineyard other than through irrigation injection.
Gypsum may be injected without the worry of lime scale formation if the pH and the bicarbonate (often expressed as total alkalinity) levels of the water are low enough. If the natural water is too high in either of these two factors, it can be modified with the injection of sulfuric acid prior to the gypsum injection point, effectively reducing the total alkalinity and pH.
Fertigation using gypsum can help to flush sodic soils of high sodium concentrations that have built up over time from using irrigation waters that are high in sodium. The Ca in the gypsum will replace the Na on the soil exchange complex allowing the irrigation waters to flush the sodium through the soil profile. You need to apply enough water to exceed the evaporation needs of the crop to assure downward movement of water through the soil profile and past the root zone in order to move the salts out of the profile.
Fertigation also reduces soil compaction as it reduces the number of trips across the field with heavy equipment. It allows for timely application of nutrients when they are needed by the crop and nutrients can be uniformly applied across a field.
As far as rates for gypsum, it will all be determined by your calcium and sulfur needs. The benefit of fertigation is a grower can spoon feed the nutrients and time his applications. Applying a low rate several times will really help when the nutrient solubility is low.
The Blogronomist is maintained by Craig Dick, head blogronomist and VP of Sales and Marketing. Here you will find a wide array of blog articles from Craig and expert guests on topics related to soil and crop health, farming, and so much more. If it’s not here, ask us!