Cover Crop Benefits

Catchment Sensitive Farmers Meeting

I had a really fascinating day in Dorset today, exploring the use of cover crops to capture nutrients, (mainly nitrates) and stop them being washed through the soil profile and into ground water. The day was organised by Wessex Water and the Catchment Sensitive Farming organisation. Fellow Nuffield Scholar Tim Stephens and his team have put together a matrix of different cover crop species and seeding rates to look at establishment, nutrient capture and suitability within the field. The catchment also has porous dotted around the fields and every 2 weeks from October to the end of January samples are taken and the levels of nitrate in the water assessed. These values are then turned in to a Kg/Ha of nitrogen to give farmers a vital guide as to where leaching is occurring in the farming rotation and how much is being lost and when leaching occurs.

It seems that the worst leaching occurs after Oilseed Rape and Wheat, probably due to the higher levels of fertiliser they receive but also due to the very inefficient way these plants use the applied nitrogen. Wheat for example is only about 60% efficient when looking at applied or synthetic nitrogen fertiliser. Where cover crops are used the leached level of nitrogen is about 50% that of land farmed without cover crops. This has a significant impact when looking at the catchment as a whole. It is great credit to Wessex Water that they have decided to take this partnership approach to try and reduce diffuse pollution working together with the farmers in the catchment.

Beneficial and Pest Numbers in the Cover Crops

Also on hand were a team of entomologists who have been assessing the impact of cover crops on the insect population. The picture above shows the numbers of insects trapped over a 7 day period. The 2 trays on the left show the beneficial's and on the right are the pests. The top half shows the numbers and type captured in the cover crop field (oil radish and phacelia) and the bottom half shows what was captured from a control field i.e. no cover crop. This level of detail is very encouraging. This clearly demonstrates that cover crops are hosting higher insect levels all round but significantly more beneficial insects that will predate the pests. This is so important when looking at using an Integrated Farm Management approach to try and reduce the amount of pesticides we might want or need to use. There were lots of carabid beetles, who's larvae predate slugs which is also very positive. The benefits weren't just in this cover crop species mix. the photo below shows what was captured within a buckwheat, oil radish and phacelia mix. The predator list includes, carabid beetles, springtails, harvestman spiders (not really spiders at all), ants, spiders, and parasitic wasps. The pest list includes mites, flies, aphids, snails and a slug.

Beneficial Insects and Pests trapped from Cover Crops

The session continued in the local village hall with a great presentation on 'Making the Most of Cover Crops' by Ian from Oakbank. Ian talked about different cover crop mixes, how and when to establish them, and the merits of diverse mixes and the impact of this type of farming can have to the on the bottom line and the better environment. A great day of learning.

Glyphosate - A Key Ingredient

Over-winter Ploughed field

Not that long ago, the land at Overbury would have been ploughed over the winter time to prepare it for the next crop.  This is a destructive process for all of the organisms; bacteria, nematodes, fungi and earthworms that live in the soil.  It was the only way farmers had to control weeds and create a seedbed suitable for our equipment to plant the seeds into.   Many fields destined to be planted in the spring would have been left in this ploughed state over the winter period.  We now know that is method of land preparation; and we are catching up with the rest of the world, is a very bad practice for many reasons.

The most significant reason is that we are adding air to the soil, which reacts with the carbon locked in the soil, releasing Carbon Dioxide (CO2) into the atmosphere, a significant ingredient in global warming, adding to the changing climate threat.  The tractors that we use release Nitrous oxide as they burn the diesel, (just like diesel cars) and ploughing uses a lot of diesel.  Moving the soil also destroys its structure, meaning that small particles of silt, are washed through the soil taking pesticides and fertiliser with them.  They wash down to the depth of the cultivation and fill in the pores resulting in the surface level water logging.  This water logging means that any subsequent rain can't infiltrate into the soil and so runs off causing surface erosion. Soil erosion can be reduced by 90% buy not cultivating and using Conservation Agriculture techniques. The soil particles end up in the streams and water courses silting up the stream beds, reducing water flow capacity and can potentially lead to flooding further down stream.  

There are the soil inhabitants to consider as well.  Cultivation destroys their habitat and their food supply and we need them to help our plants (and therefore our food), to collect nutrients from the soil.  Worm populations can be reduced by 50% by ploughing.  We need the worms to aerate the soil, digest the soil and restructure it, adding glomalins (glue) to stick the particles together and recycle dead and decaying plant materials.  A healthy soil is one that can sustain itself with as little human interference as possible and that means not cultivating.

A field after winter with cover crops

Soil is also greatly improved by keeping it covered, using plant material or previous plant residue, a theory nicknamed 'soil armour' in the U.S. This concept uses plants to intercept rain droplets, keeping the soil surface open and aerated.  The plants in the picture above have been growing all winter, capturing available nutrients, taking carbon from the atmosphere and locking it up in the organic matter of the plant, restructuring the soil, feeding our soil biology and providing a brilliant habitat for birds and mammals, Our cover crops this year have hosted brown hares, starling, redwing, field fare, lapwing, meadow pipets, yellow hammer, chaffinch, linnets, snipe, woodcock and many others across these fields.  Compare that to the ploughed field above where it is mainly lifeless.

From the environments point of view cultivation's are not a good idea.

So why the long blog about protecting the soil?  Well this method of farming, called no-till or zero-till, is under threat from misinformed lobby groups trying to get the active ingredient 'glyphosate' banned from all of our European crop production systems.  It is a very safe herbicide, (weedkiller) that we use instead of cultivation to kill weeds and cover crops, prior to planting our next crop.  It has been a valuable tool available to farmers for the last 40 years. Without glyphostate there will be serious implications to our food security and the negative effects of cultivation, (listed above) in terms of mechanical weed control will return.  It is used across the world and is one of the most rigorously tested of any pesticide, that is currently registered for use.  An EFSA (European Food Safety Authority), concluded in a peer reviewed report (published EFSA Journal 2015;13(11):4302in) 

"glyphosate is unlikely to pose a carcinogenic hazard to humans and the evidence does not support classification with regard to its carcinogenic potential".

The only body to conclude that glyphostate might pose a health risk is the IARC (International Agency for Research on Cancer) who concluded it is "probably carcinogenic to humans".  According to the IARC's own classifications glyphostate is in the same category as drinking very hot drinks, working as a hairdresser and working night-shifts.  Glyphostate is safer than orange juice, bacon and indeed coffee, so we need to keep it in perspective and look at the benefits it delivers in globally feedin the world.

Without glyphostate, as part of an Integrated Farm Management approach  UK yields of wheat and oilseed rape (canola) will drop by about 20%, primarily due to weed competition.  We will need to use 546,000 Ha more land to replace this lost production.  Our farms will not be able to compete with other growers using it around the world. Profitability would fall and cheap food imports will be sucked into the country; in many cases produced to lower environmental standards. Mechanised weed control, including ploughing will return; reducing our soil organic matter, biological life, disruption to ground nesting birds and fewer environmental benefits. It will be a gloomy picture.  

We need to look at the whole system to appreciate how decisions impact on each other and if the cause and effect can be beneficial or not.  Nothing is simple or black and white.  I know that not being able to use this proven, safe chemical will impact severely on what we do and how we do it; eroding the positive environmental benefits of no-till farming.

No-till planting Into Cover Crops