Martin Dairy Ltd in Cornwall on soil health and nutrition

With 950 dairy cows and 750 ha of cropping, Martin Dairy Ltd is a large enterprise that recognises the importance of being as resilient as possible to the environmental and financial pressures facing the sector.

The farm grows a range of crops, including forage maize, winter wheat for crimping, winter and spring barley, forage rye, and grass, on predominantly silty clay loam soils, much of which is rented from local landowners.

Richard Martin, who heads the arable operations, believes soil health is at the heart of improving resilience. He is working with Hutchinsons agronomist, James Whatty, to make some significant changes.

Traditionally, the business has operated a plough-based establishment system, but Mr Martin knows this can present challenges in some seasons, and believes reducing tillage intensity is key to improving the soil’s resilience to more extreme weather.

With that in mind, during autumn 2022, he hosted a direct drilling demonstration on a field coming out of maize going into winter barley. Before the demonstration, a Healthy Soils Gold test was conducted on the land to better understand the soil characteristics and the most appropriate management techniques for it.

Mr Whatty says testing confirmed soils were generally in good condition, with high organic matter content at 7-12%, and high fertility (N, P and K) given the use of organic manures and slurry over many years. The buffer pH was also relatively high at 7-7.5, indicating soils will naturally revert to a higher ‘resting’ pH.

The carbon:nitrogen ratio was very low though, at 7.5:1, when the optimum is 24:1.

“With large quantities of organic manures applied through the rotation, this low ratio means nitrogen can be rapidly released from the soil through mineralisation, potentially meaning we are not fully utilising the nitrogen within the system," Mr Whatty said.

 This is something they are looking to manage with more tailored cover crop mixes.

Although the farm has not converted to a full direct drilling system, non-inversion tillage is now used for establishing cereals, based around a Sumo Trio and a 3 m Pottinger combination drill.

“We haven’t ploughed anything for autumn cereals for two years now,” said Mr Martin.

“It’s been a big change, but considering how wet it has been over the [2023/24] winter, our fields travelled reasonably well this spring because they haven’t been ploughed.

“I’m not saying it’s perfect; there are still problems to overcome, but it’s definitely quicker, is saving us a bit of money on establishment, and I feel is doing a better job by letting the soil do some of the work for us.

"We find ploughing is a good way of aerating the soil and creating a nice seedbed for maize to go into, and helps us incorporate organic matter.

“Saying that, we’re keen to try new approaches. We’ve trialled a Horizon strip-till drill for maize, but the kit is very specialist, and last year we tried drilling some maize with the cereal drill, which worked okay, but still wasn’t as effective as the specialist maize drill. Ideally we’d like one machine capable of doing everything.”

As part of the focus on soils, Mr Martin is also digitally mapping soils across the farm using Terramap high definition scanning, which provides a comprehensive picture of all common nutrient and physical soil properties in far greater detail than conventional grid sampling, mapping over 800 data reference points per hectare.

So far, around 65 ha has been Terramapped, and he hopes to have the whole arable area scanned on a rolling basis over the next five years, with results uploaded to Omnia for analysis.

“Terramapping has already opened my eyes to the variations in some fields,” he added.

“The first fields we mapped were on sloping land deliberately chosen because it was likely to be more variable, but even so, some results were still a surprise. Phosphate and potash, for example, showed particular variation, with higher levels at the top of the slope than further down, which was the reverse of what I expected.”

Mapping in-field variability has opened the door to variable input applications, principally fertiliser, but he also plans to try variable seed rates on cereals this coming autumn.

They have also started using micronutrition starter fertilisers in maize (Primary-P), to reduce reliance on DAP, which has historically been applied at a flat rate on the drill. Variable rate starter fertilisers are a future possibility, although this will require investment in a new drill, so Mr Martin wants to be confident in the approach before making such a move.

Last season, they also tried reducing DAP rates on one block of land with high P indices, with no starter fertiliser, and maize performed well with no obvious yield differences to the standard DAP approach.

Elsewhere, variable rate nitrogen is being tried for the first time this spring on an 18 ha block of winter barley. Rates were varied according to NDVI imagery available through Omnia, with more nitrogen applied to boost lower biomass areas, and less to denser parts. From a baseline of 85 kg N/ha, rates varied by +/- 15-20 kg N/ha, Mr Whatty notes. 

Last season, a foliar bacterial nitrogen-fixing product was also trialled, to see if it could help better utilise high levels of soil nitrogen. Mr Whatty says results were encouraging, with a 1 t/ha yield response, so it is something they plan to try again this season.

If variable fertiliser applications prove successful on cereal ground, Mr Martin hopes to expand its use to the grassland and maize areas in future, possibly including variable rate slurry applications, although again, he needs confidence it is the right approach before investing in any new equipment.

Cover crops are an important part of the rotation, with 40-60 ha in the ground most seasons, usually to protect soils over the winter, between winter barley harvest and sowing maize the following spring.

Mr Martin has previously favoured forage rape for this, grazing it off over winter with either cattle or sheep.

“However, in wet winters, cattle can cause some damage to the soil, so we want to explore alternative mixes that are more tailored to what the soil needs, but can still be grazed by sheep,” he said.

A secondhand 6m Vaderstad Rapid drill has recently been purchased primarily for sowing cover crops behind winter barley, but Mr Martin also plans to try using it to over-sow legume and herb seed into existing grass leys as part of the Sustainable Farming Incentive herbal leys option (SAM3).

Farm Facts: Martin Dairy Ltd, Trethick Farm, Bodmin

• 950 dairy cows + 800 followers (Swedish Red cross Holstein dairy cows averaging 9,000 litres)
• 750 ha of cropping (110 ha owned, most rented)
• Cropping includes maize, winter wheat, winter and spring barley, forage rye, grass
• Soil type is mainly light loams with some heavy clay
• Currently hosts Helix Cornwall demonstration
• Using Terramap and Gold soil testing to tailor management and input use
• Initial focus on cereal ground, but plans to expand the approach to forage crops in future