Max Purnell was a dairy farmer, now raises dry stock. His interest in improving soil has spanned at least two decades, and he has farmed to “grow the soil”.

For the past 5 years he has experimented with a “rolling fallow” – rotating around the farm allowing some paddocks to grow unharvested except for occasional light grazing to remove seedheads. Fertiliser has not been used for some years and he believes that with his system he has increased soil depth and quality, and at the same time sequestered a considerable amount of carbon.

He postulates that NZ could meet its Kyoto obligations easily by managing pastures to increase soil carbon, and there is some evidence for this. By improving soil he believes it would also improve the quality of pasture as a feed and hence the quality of animal products produced.

His farm is 89 hectares, 60 flat and the rest rolling. Also 30 on a runoff a few km away. The soils are clay marine sediment. 30 years ago Max drained the flats.

Soil carbon is a measure of “life” in the soil. Conventional wisdom is that pastoral farming increases soil carbon, but recent research has shown that some NZ soils have actually lost carbon in the past two decades. There is also some work showing that use of superphosphate and nitrogen to boost pasture growth has the effect of reducing soil carbon.

Organic farmers and those who farm “biologically” without manufactured chemical fertilisers would argue their efforts to encourage soil biology – the growth of soil bacteria, fungi, worms etc – plus the use of a wider range of pasture species results in the build-up of soil carbon in the form of plant roots and a multitude of soil organisms.

Max Purnell has been interested in nurturing the soil on his farm ever since he bought the property 30 years ago. He gave up use of superphosphate early on and used RPR (Reactive Phosphate Rock) and some minerals instead. He was persuaded by a geologist cousin that most of the elements needed for pasture growth were actually present in the subsoil, it was a matter of increasing plant root depth and carbon in the soil so that these minerals could be made available.

Through careful drainage of swampy land and nurturing of broadleaf species in pastures he has built up a sustainable sward that he has seldom had to replace. The depth of soil has increased steadily, and he has found that the roots of certain plants penetrate deep into the subsoil.

“There is a direct relationship between the amount of soil carbon and the ability of roots to access minerals through biological mechanisms,” says Max.

“When I first came here the root depth was probably only about 200mm because it had been farmed traditionally with super, was wet and well compacted and a roller was used on the property. Now in some places it goes down 1m.”

Max has found that modern varieties don’t survive long term and he believes it is better to use older more permanent pasture types. He encourages broadleaf species, and has found that plantain and even buttercup are palatable to stock when grown in his improved soils.

“Some scientists are concerned that there is poor uptake of these new, high producing cultivars, but the reality is that they require large amounts of chemical fertilisers and don’t work in the long term,” he says.

After 25 years or so of dairying he has given that away and is raising dry stock and indulging his interest in soil building.
His beliefs are:
• The soil is the most important aspect of the farm
• There are many ways of building it effectively
• The amount of carbon that can be restored to soils can directly influence our food security and climate change in our lifetime.
• If there is too little carbon in the soil, crop production is inefficient
• Carbon capture in our soil is an important strategy that can neither be ignored nor overemphasised.
• Keeping carbon locked in soils reduces the amount of CO2 in the atmosphere and also sustains and improves production. The world’s soils hold 50% more carbon in soil than there is in the atmosphere, and three times more than in vegetation.
• Soil is the largest carbon sink over which we have control
• Management can dramatically affect the accumulation of carbon in the soil

“We don’t have enough science to be certain what is happening generally in NZ soils. Most measurements have been done only on the first 150 – 300mm and we should be looking at what is going on down to 1m,” says Max.

“We need to do the work on measurement techniques and assemble data because I think we are on a win-win here in NZ. We have the perfect climate to grow soils, farmers who can show that they are using the right practices and growing their soils should get the advantage of carbon credits.”

"Several people have made ballpark calculations that suggest that if the level of carbon in our agricultural soils were to be increased each year by 0.17% in the top 10 cm alone, then all the CO2 we produce annually by all forms of activity would be sequestered into the soils, and New Zealand would become carbon neutral."

Any farmer can grow their soil, he believes, by doing the following:
• Avoid soil compaction
• Introduce broadly species into pastures
• Stop using 24D
• Wean yourself off bagged nitrogen fertilisers because in time that will come with a cost – there is a correlation between using a lot of N to produce plant protein and depletion of soil carbon
• Use RPR, not superphosphate, and get advice if you need it to make the change. Farmers put on huge amounts of super but only small quantities go off the property as animal products. The rest is lost.
• Good grazing management leaving adequate residuals.

Rolling fallow
Prior to chemical fertilisers being readily available, farmers would use a year-long fallow to rejuvenate soils. This meant either leaving the area ploughed or letting whatever was there grow unrestricted.

For the past five years Max has been experimenting with what he calls a “rolling fallow” to improve soil productivity without the need for fertilisers. Essentially he shuts a paddock up and allows the plants to grow tall. Root growth will match the top growth, and roots will go down to a greater depth. Worms and other soil fauna will also go deep and be active.

When plants go to seed they concentrate some minerals in the seed. Strategic topping of the sward by stock allows some sunlight down to the soil surface, and that and animal wastes maintain biological activity near the surface. It also prevents one species from dominating and wiping out others.

Max has found that this process has worked for him, he has been able to continue to farm profitably without applying fertiliser, and soil depth continues to increase.

Research needed
Max points out that many farmers are using biological practices that enhance soil growth, and that his is not the only way. However, they all need help to improve their results and get a better understanding of soil carbon. He strongly supports the AgMardt initiative to stimulate debate on the importance of soil and its potential role in storing carbon and mitigating climate change, and being a key contributor to New Zealand’s achieving carbon neutrality.

Says Max:
“Putting carbon into soil is a win-win for everyone - you take carbon out of the atmosphere and you improve soil function and the quality of the food that can be grown in it. Many farmers are increasing soil carbon, and many more could do a better job. They should benefit all from carbon credits.”

Rolling fallow
Prior to chemical fertilisers being readily available, farmers would use a year-long fallow to rejuvenate soils. This meant either leaving the area ploughed or letting whatever was there grow unrestricted.

For the past five years Max has been experimenting with what he calls a “rolling fallow” to improve soil productivity and growth. Essentially it is fast light strip grazing, using electric fences, of a paddock in which the plants have been allowed to grow tall. Root growth will match the top growth, and roots will go down to a greater depth. Worms and other soil fauna will also go deep and be active.

When plants go to seed they concentrate some minerals in the seed. Strategic topping of the sward by stock allows some sunlight down to the soil surface, and animal wastes maintain biological activity at the surface. It also prevents one plant species from dominating and wiping out others, and conserves moisture so that worms and other soil fauna will remain active and not die or hibernate.

The rolling falllow improves on the old style fallow in which ground was largely left bare and dried out, reducing soil life, or pastures were allowed to become rank and formed a blanket of one species. In both cases it could take a year or more for the pasture to recover from the fallow and become fully productive again.

Max has found that this process has worked for him, he has been able to continue to farm profitably without applying fertiliser so far, and soil depth continues to increase. Note that part of the reason for no fertiliser being needed is that he has put on a lot of RPR and minerals in the past. He believes that deficiencies will inevitably show up, but the amounts needed to correct them will be small.

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