Using gypsum to improve soil health, water quality and fertiliser use efficiency

The second applications of gypsum have largely been made. 

Farm Carbon Toolkit are gearing up to come out in October/early November to complete the post-application soil assessments

Grain sample results should be back soon, so the group can start to draw up preliminary results from year 1. Year 2 data will be needed to make some full conclusions. 

Spring gypsum applications took place between 19th February and 19th April on arable fields growing winter cash crops (winter wheat and OSR). Gypsum applications took place between 27th March and 2nd June on arable fields entered into agri-environment schemes, with one field still yet to receive gypsum (as of 24th June).

N-testing took place weekly on three fields growing winter wheat between 24th March and 2nd June to measure crop nutrient uptake. N-testing uses a handheld chlorophyll meter from Yara to scan growing leaves, measuring light absorbance of the leaf to calculate chlorophyll content and, thus, nitrogen content.

 Measurements were taken from control (no gypsum) and trial (gypsum applied) plots in each field for comparison. For two of the fields, N-tester values did not differ substantially between control and trial plots. For the remaining field, N-tester values were consistently higher in the control plot than the trial plot, suggesting better crop growth in the control plot. While this could reflect a negative impact of the gypsum, it is more likely caused by variation in crop growth throughout the field that was already present before the application of gypsum (see satellite imagery).

During this spring growth period, Yara’s software was also used to explore satellite imagery measuring plant biomass across all fields in the trial. It was hypothesised that control plots would be visible due to poorer crop growth compared to trial areas, however there was no obvious visible difference in any of the fields.

In conclusion, there is not yet any evidence to suggest a positive impact of gypsum application on crop growth, however further gypsum applications are planned for later summer/early autumn (after harvest) on the same fields.

Gypsum is most effective when applied directly to the soil during cultivations or at the point of drilling, therefore it’s possible that spring applications on growing crops this year may have compromised its effectiveness, especially considering the recent dry weather.

Post-application soil health assessments are due to be completed in autumn 2025 and will help to provide a definitive assessment of the impact of gypsum.

Most of the farms have now applied their gypsum for the spring. A second application will take place in Autumn 2025.

N testing is now taking place on three of the winter wheat fields, and the group are using a chlorophyll meter to check crop nutrition.

The first round of soil assessments took place in autumn (2024), and the second round will take place in Autumn 2025, as will water quality testing. 

So far 7 fields have received the gypsum since February, with 3 still to go, dependent on cultivations, crop establishment and grass cuts.

As yet there are no results that positively show the gypsum has affected either crop nutrition or growth, but it is early days.

The triallists are preparing to complete their first application of liquid gypsum. The original trial planned for this to take place in the autumn, but wet weather conditions meant that this was delayed until the spring.

The triallists will be using the following application guidelines:

• All rates are 10L/ha, and the product contains 6% calcium and 10% sulphur.
• For spring crops gypsum is best applied to the soil after/during the final cultivation.
• For growing crops the gypsum is best applied to the crop just before, or during, a rain. This sounds counterintuitive, but the aim is that the product be washed off the leaves so it reaches the soil.
• Liquid gypsum should not be mixed with liquid fertilisers, micronutrients in suspension or herbicides. These will all have to be applied in a separate pass.
• The product is highly soluble and at high risk of leaching, so triallists must ensure the weather conditions and soil temperatures are right.  As the temperatures warm and biological activity increases an appropriate time to apply should be coming up.
• Gypsum will be applied only to trial plots, not to the control plot. The coordinator will ensure this is carried out correctly.

In October the group met online to plan the next stages of the trial. and instruct the farmers on methods and timings of gypsum application. At this meeting a collective decision was made to postpone gypsum application to spring 2025, when its effectiveness will be enhanced due to warming soil temperatures and more active soil biology.

In November initial baseline soil testing for pH, P, K, Mg, Ca was carried out at each of the farmers' trial sites, along with soil health assessments completed by Farm Carbon Toolkit.

Gypsum has been purchased and delivered to facilitator and begun distribution to farmers.

The next step will be application of gypsum in the spring.