Applying gypsum methods
Applying gypsum methods depend on whether the agriculture is dry land or irrigated, whether the topsoil or subsoil (or both) is to be treated and the nature and extent of the problem.
1- Injection of saturated gypsum solution, gypsum suspension into the irrigation water can be used for two primary reasons: (a) to add Ca as part of the overall Ca amendment program for sodic soils, and (b) to add salts to ultrapure low-salinity irrigation water to increase ECw and water infiltration. This latter reason is not a sodic soil issue.
Injection application methods that can add higher quantities of gypsum via the irrigation system than traditional fertigation systems include (a) devices that create a saturated gypsum solution by percolation of water through fine-grade gypsum; (b) devices that use agitation in a tank to suspend and dissolve Ca from fine-grade gypsum and (c) a system that uses a cone-shaped tank with a wobbler spray head at the bottom with a stainless steel cone on top, which allows water-soluble dry material to be turned into a suspension with further dissolution into the irrigation lines. This latter system is simple in design, operation, and cost.
2- Broadcast application using a fertilizer spreader to treat top soils. Rain and irrigation will dissolve the gypsum. Gypsum is best applied well before sowing to maximize subsoil water storage, particularly under dry land conditions. For best results, the spreader should have a stainless steel box with slick, steep sides, twin spinners and a wide delivery chain or belt. A delivery chain unloads material from the front of the spreader allowing material to flow freely with less bridging potential than that of a belt. Ideally, sides should slope at a 45-degree angle and the exposed portion of the belt or chain measure at least 20 inches in width.
3-For sodic soils if it was decided to add all the gypsum during this pre establishment period, then 75% may be spread over the site and mixed to 12 inches, followed by 25% mixed in the surface 4 inches. If the soil is of intermediate texture but sodic, gypsum addition to 6 inches may be adequate.
4-On bare soils, gypsum will be assisted by any tillage operations, which promote better conditions for water movement by creating temporary structure and pore continuity improvements. However, the addition of organic matter throughout the depth of gypsum treatment will be of great benefit and provide more pronounced positive results.
5- Deep tillage, helps to incorporate gypsum into the subsoil but should not be done unless the subsoil is dry, otherwise considerable structural damage will result.
6- Concentrated gypsum suspensions can be injected into or deeply mixed with sub-soils, but the machinery is expensive. Deep placement via shrinkage cracks appears to be the most economic approach.
Gypsum Handling and Storage
Gypsum, is not combustible or explosive. Gypsum is also not expected to produce any unusual hazards during normal use. Under ordinary conditions, no glasses or goggles, gloves and protecting clothing, and respiratory protection are required for handling of gypsum. However, exposure to high dust levels may irritate the skin, eyes, nose, throat, or upper respiratory tract.
Therefore, as much as possible, minimize dust generation and accumulation and avoid breathing gypsum dust. In storage areas, provide ventilation sufficient to control airborne dust levels. If dust is being generated, wear the appropriate eye protection, such as safety glasses or goggles, and a dust respirator.
Gypsum may be stored in the open or in a covered structure. Gypsum storage should accomplish the following goals: (1) Minimize water interaction; (2) reduce dust; (3) balance capital investment, cash flow requirements, and labor costs, and (4) maintain good physical condition of the gypsum for spreading. Gypsum storage is needed to provide handling and spreading flexibility.
Spreading is often seasonal and needs to be scheduled to avoid wet ground, poor weather conditions, growing crops, and conditions conducive to causing pollution. Storage areas or facilities should be constructed to minimize any potential dust, surface water runoff problems, and access by animals through proper fencing.
Although higher in cost, a covered structure may be practical due to improved handling conditions, less or no surface water runoff, and less spreading of dust. Water runoff from gypsum stockpiles, whether from rainfall or snowmelt, may contain unaltered gypsum and soil. If gypsum is stockpiled in an individual field for post-harvest application and then completely spread before winter, no
action is needed other than that of constructing a temporary storage pile. If gypsum is stored in large piles in an open-lot system, a management plan should be developed to avoid dust and water problems from developing and to restrict cattle access. Runoff can be collected and transferred to a settling basin or holding pond by constructing diversion, curbs, gutters, lot paving, and, in some cases, by pumping.