Written by Will Steel
Calcium and Sulphur: Overlooked Macro Elements or No Concern?
After a somewhat disappointing harvest for some of my farmers in Kent, where yields varied from 6 to 9 t/ha averages, the post mortem inquest started early as the grain was coming into shed.
The Impact of Wet Weather on Soil Nutrients
With the continuing cycle of wet harvests and wet winters for the last 4 years in this part of Kent has led in my opinion to Calcium and Sulphur being leached out over winter. 2 key elements for yield and nitrogen use efficiency.
Optimising Soil pH for Nutrient Availability
With soil pH in arable crops ideally being around 6.5 to make the most effective use of all macro and micro nutrients and maintain biological activity, it remains along with drainage, a fundamental starting point for making most of expensive nutrient inputs. In dry years of < 700mm of rain (that is dry for my part of West Kent/Sussex prior to 2018) I was finding on my farm that pH levels using sewage cake, fym/compost and chopped straw were relatively stable. Post 2018 when average rainfall has exceeded 960mm p.a I was beginning to question poorer performing areas of all crops. Grid testing per ha revealed pH ranges on farm from 5.2 to 7.3.
Strategies for Correcting Soil Acidity
Tackling the acidity question I’m trying to persuade my agronomy farmers to go for more detailed soil pH testing on a GPS located 1 ha basis with an approx. cost of £4-5/ha. This should give them a coloured zoned map to give to their lime contractor next summer after harvest. Hot spots we will aim to sort out with Calcifert at rates between 150 -350 kg/ha as soon as we can travel in the spring with the view to come back with longer term solutions of crushed chalk at no more than 3 t/ha variable rate applied at harvest. Getting the soil biology to deal with more than 3 t/ha of lime in one go is a big ask and I’d prefer to do this over a number of years, testing in between if necessary. Lime is expensive at £19-35t/ha so over enthusiastic liming should be avoided.
Addressing Sulphur Deficiency in Crops
Having hopefully sorted out the correct pH in the soil,I was concerned that most of the sulphur we apply has either been applied too early (overwinter as gypsum perhaps , in too small an amount too early, or has just been leached out by incessant rain over the winter, spring and the summer. I think we just don’t apply enough SO3, where its impact is far reaching on yield, quality and optimisation of nitrogen ( Farmer A).
Evidence of Sulphur Deficiency and Solutions
Data levels from NRM and Lancrop, either tissue or grain have shown decreasing levels over the last two years – 40% samples were deficient and 70% of samples low or slightly low. Taking grain off the combine for analysis has shown in my attached spreadsheet, where in a wet year optimising Nitrogen Use Efficiency levels by keeping adequate sulphur available at all times in the spring not winter has helped produce better yields of milling wheat that meets spec ( Farmer D ). I am suggesting using sulphur all the way through this year either as liquid 37/14 or solid 38/0/0 19 to avoid leaching problems. IF NUE in crops last year in low sunlight high rainfall situations was say 50% and if we can get that to an optimistic 60-70% we can grow better quality higher yielding crops with less Nitrogen.
