Don’t waste chance to up yields with green compost

Green waste compost (GWC) can increase winter wheat yields in three out of four years, according to the findings of a New Farming Systems project by NIAB TAG with an average response of about 7%.

“The yield improvement was not consistent every year in a four-year continuous wheat rotation,” says Ron Stobart of NIAB TAG. “The second wheat yield was down on the compost-treated plots, but this was probably due to them being tricky to grow anyway and seasonal variations in the breakdown of high lignin content, woody matter in the compost.”

GWC was broadcast at 35t/acre on the light sandy clay loam Morley soil and was incorporated quickly afterwards to prevent it blowing away.

Mr Stobart describes this as only a light dusting in practice, although it sounds a lot. He says commercially the compost can be applied with a muckspreader then lightly harrowed in. The amount that can be used will be determined by Nitrate Vulnerable Zone limits.

It may be possible to apply and incorporate with drilling, but this has not been trialled, he adds.

Phil Wallace, an independent environmental consultant who has 10 years of experience of compost trials for Levington, over seven different sites, confirms the yield advantages.

He says that from 1999 to 2009 there was an average 5%, yield increase in cereals, but it took three to four years before the advantage was seen.

Compost was applied at 30t/ha, some with and some without fertiliser. The trials were carried out over rotations that included sugar beet, oilseed rape or potatoes and there was a 7% yield increase overall.

Muntons, the maltsters, is also enthusiastic about the advantages of GWC (BSI PAS 100 quality standard) on spring malting barley crops. The low-carbon agenda trials, on 36ha in two fields on the Yorkshire Wolds have shown 0.66t/ha increase in yields.

“The quality was excellent and there was no difference in growth pattern,” according to its grain supply chain manager, Mark Ineson. Compost was applied at 25t/ha and ploughed in.

“Yield advantages are due to improved soil nutrient status, better water infiltration rates and better water retention,” explains Mr Stobart.

“In terms of use we found some good practical differences. There was quicker water absorption and less run-off so there was a lower risk of diffuse pollution. The moisture was kept where the plant could access it for longer.

Yield response graph

Phosphate, potassium and magnesium in particular tend to accumulate in the soil surface so over time you might expect to see more improvement in levels.”

The trials show there is an increase in soil organic matter in the top 10cm of 0.4-0.5% over the four-year period, with no difference seen at 20cm depth.

To put this in context, Mr Stobart says that a 26-year long-term straw incorporation trial only showed a 0.2% increase in organic matter. So compost produces a very big change over a relatively short timescale.

The farm manager at Morley, David Jones, says in his experience the quality of GWC can be an issue. He has seen bottle tops, plastic bags and even knives and forks mixed in with the compost, which was predominantly from household garden waste, but did include some composted food waste.

He advises making sure that only PAS 100-certified material is used to minimise importing any unwanted rubbish on to the farm.

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