Amendment Applications

Gypsum Applications on Delmarva

Gypsum is commonly noted as an amendment to relieve soil salinity, however it also requires leaching of Na to be effective. Salinity in many Delmarva fields is concentrated at lower elevations which boarder tidal sources (wetlands, creeks, bays). Therefore, farmers and landowners may potentially have only need to apply gypsum to limited regions of the field. As salinity may only exist along these edges, applications can be concentrated their, but the use of variable rate prescriptions and applications may also be performed.

Salinity Mapping

To perform variable rate applications, a map of salinity must be created. This can be performed through grid or management zone based sampling, which are standard within precision agriculture. One method to create a zone based sampling is through the use of apparent electrical conductivity (ECa). This method measures bulk soil conductivity, which will be related to soil characteristics, including moisture and salt content.

Field maps of ECa can be used to slectively sample across salt zones, where Na and other salinty measurements can be performed to determine where gypsum may be most effective.

A field with circular points across it in blue and gold to signify salt content.

ECa map of a SWI field is similar to aerial imagery of bare soil patches.

Map of Potential Salinity Amelioration

Soil samples can be used to create maps of soil salinity. Gypsum is recommended based on reducing either the exchangeable sodium (ESP) or sodium absorption ratio (SAR). In this figure, any SAR below 6 is considered ideal, so only the regions of the field in either orange (SAR 6-13) or red (SAR 13-22) are considered for gypsum applications.

A field map from an aerial view where red and yellow colors indicating salt content.

Map of sodium absorption ratio (SAR).

A field map with interlocking sqaures layered over it Blank colors indicate that no gypsum will be applied while blue and gold colors indicate where it can be applied.

Variable rate prescription for gypsum on a SWI field.

Variable Rate Prescriptions

This map of gypsum rates is based on recommendations from arid climates, and may not reflect the actual needs of Delmarva soils. However, this type of research must be performed to ensure we have an understanding of what is needed.

For this field, based on SAR measurements, gypsum application rates range from 0 to 2000 lbs per acre. This will allow farmers and landowners to target application where it may be needed most, while avoiding regions where it is not needed.

Organic Soil Amendments

Organic amendments such as compost, manure, poultry litter, and biochar may help improve some of the soil properties affected by salinity and sodicity. Adding organic matter can improve soil structure, water movement, and biological activity, which may help affected soils recover when combined with adequate drainage and fresh water for leaching.

A pile of compost that is dark brown in color in front of corn that has turned brown.

Compost is a common soil amendment to build carbon in the soil.

Research on organic amendments for coastal agricultural soils on the Delmarva Peninsula is still developing. Producers should test both the soil and amendment before application and consider amendment salt content, nutrient loading, and the ability of the field to drain and leach salts.

Some amendments can also contain substantial amounts of soluble salts, so applying high rates to an already salt-affected soil could increase salinity rather than reduce it.

A pot with brown soil in it and one green plant.

A soybean plant germinating in a mixture of SWI soils and organic amendments.

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