Estimated reading time: 10 minutes
- There is a misconception that fertilisers and regenerative agriculture are two opposing concepts in agriculture.
- An important factor to consider is the soil biology and organic matter as it drives agricultural systems.
- In terms of nutrient cycling, often overlooked are the important differences between natural forests and grassland on the one hand, and agricultural production systems on the other.
- It is important to note that nutrients removed from fields in grains and other food products are mostly not recycled, but are permanently lost through waste and sewage disposal systems. A key consideration therefore is that for any form of agriculture to be sustainable, removed nutrients must be replaced.
- Importantly, in their natural state, most soils in the higher rainfall eastern half of South Africa have severe nutrient deficiencies, and can only be made productive through inputs of either inorganic or organic fertilisers.
An important tenet of regenerative agriculture is reduced use of inputs, in particular fertilisers. In fact, often touted in regenerative circles is complete cessation in the use of ‘hazardous chemical fertilisers’.
In this article I will focus on nutrient balance and cycling in pastures and crops, consider the impact of soil biology and organic matter in these processes, and draw attention to the role of fertilisers for the long-term sustainability of production systems. As Prof Derrick Moot of Lincoln University in New Zealand notes: “It is important that sound science drives our agricultural systems”.
In terms of nutrient cycling, often overlooked are the important differences between natural forests and grassland on the one hand, and agricultural production systems on the other. The former two are essentially ‘closed’ systems, with the nutrients taken up being efficiently recycled to the soil through leaf and foliage drop, and root decay.
Importantly, essentially no nutrients are removed from the system. High topsoil organic matter levels contribute to the retention and slow release of nutrients, while the presence of legumes and free-living nitrogen-fixing bacteria in most of these ecosystems contributes greatly to their nitrogen (N) economy.
In contrast, agriculture involves a continuous loss of nutrients from fields through the harvesting of products. It must be pointed out that in the case of dairy cows grazing pastures, nutrient removals are far greater than those contained in only the milk, since substantial amounts of nutrient-rich manure and urine are deposited in roadways, holding yards and milking parlours; our research indicates that on a typical dairy pasture, 50 to 100kg/ha of potassium is lost annually.
It is important to note that nutrients removed from fields in grains and other food products are mostly not recycled, but are permanently lost through waste and sewage disposal systems. A key consideration therefore is that for any form of agriculture to be sustainable, removed nutrients must be replaced.
The aforementioned considerations are essential to bear in mind when the frequent argument is made that ‘natural systems need no fertilisers, yet are highly productive’. A prominent soil biologist and regenerative agriculture proponent – widely followed on YouTube – in decrying the use of fertilisers, stated: “No-one is fertilising the rainforest”. Yes, but no nutrients are leaving the rainforest! Natural forests and grassland would soon collapse under a regime of continuous nutrient removals.
Soil biology and organic matter
Can favourable soil biology and organic matter levels enhance nutrient supplies and reduce or even obviate the need for fertiliser additions? Here, some clarification of the role of biological nutrient cycling is warranted – there all too often appears to be confusion among the proponents of regenerative agriculture regarding the potential of this process.
Certainly, symbiotic N fixation in legumes offers enormous opportunities for providing nitrogen, and thereby reducing requirements for N fertilisers. A soya bean crop may fix in the region of 150kg N/ha, while stands of lucerne and clover typically fix from 100 to 400kg N/ha. However, the potential for legume N to completely replace fertiliser N in food production is remote; currently around half of the total food production in the world is dependent on the use of N fertilisers.
What about other essential plant nutrients? Unfortunately, the potential of biological nutrient cycling to contribute to the supply of other important plant nutrients, such as phosphorus (P), potassium (K) and zinc (Zn), is minimal. As noted in my earlier article, soil biology cannot make nutrients. Nor can organic matter make nutrients.
Yes, higher organic matter levels and a humming biology will result in better nutrient uptake through healthier and more prolific root systems. But the biology cannot manufacture additional supplies of these nutrients. It is true that mycorrhizal fungi are able, in some soils, to improve the availability of existing supplies of nutrients such as P and Zn; however, research shows that this mechanism usually falls far short of meeting the immediate requirements of fast-growing crops.
Importantly, in their natural state, most soils in the higher rainfall eastern half of South Africa have severe nutrient deficiencies, and can only be made productive through inputs of either inorganic or organic fertilisers.
Compost, manure and fertiliser
Is the use of compost, manure and organic fertiliser a viable alternative to the use of conventional fertilisers? Producers are generally well aware of the significant benefits of compost and manure in terms of improving all aspects of soil health and, most importantly, in enhancing water infiltration and retention.
Where available, every effort should be made to apply these products to fields. However, the following considerations need to be borne in mind:
- Use of these products is more often than not limited by their availability. There is just nowhere near enough for the requirements of the vast areas of cropland required to feed the eight billion people in the world.
- Manure and compost are bulky and have relatively low nutrient concentrations. Transport and application imply additional logistical costs relative to the use of inorganic fertilisers.
- All too often overlooked by regenerative and organic farming proponents is that the use of organic products to supply nutrients is inevitably a case of ‘robbing Peter to pay Paul’. This is because areas used to produce the compost or manure are depleted of nutrients, with these nutrients then being applied to production fields. The fertility of the areas producing the organic products is therefore in constant decline. Thus, there is an underlying issue of a lack of sustainability in the use of organic products as a substitute for fertilisers; this is generally ignored (or possibly not understood) by the advocates of these farming systems.
- There is general consensus among realistic agriculturalists on both sides of the debate that yields per unit area are generally lower with zero-fertiliser farming (organic or regenerative) relative to conventional farming practices. This being the case, a large-scale conversion to zero-fertiliser agriculture – even if possible – would imply a need, on a global scale, for the allocation of substantially more land for food production. Where is this land to come from – deforestation?
- With respect to specialised commercial ‘organic’ fertilisers, their value hinges essentially on the amounts of plant nutrients they contain. The amounts of organic matter contained in them is insignificant relative to the total organic matter content of soils, and any claims that they are of use in building soil organic matter levels are essentially without substance.
Fake news and popular myths
Unfortunately, misinformation regarding the properties, impacts and use of fertilisers abounds. Following in brief are four examples of this, and the associated scientific facts.
Fertilisers ‘burn up’ the soil organic matter
On the contrary, fertilisers increase crop and pasture yields, and thereby contributions from roots and crop residues to the soil organic matter. Furthermore, since organic matter acts as a reservoir for plant nutrients and contains substantial amounts of nutrients such as N, P and S, it is not surprising that a wide body of research reflects the benefits of fertilisers on soil organic matter levels.
Fertilisers kill the soil biology
Research studies, both locally and overseas, have repeatedly shown that fertilisers – used at rates required for optimum yields – serve to benefit and promote the soil biology, rather than have harmful effects. Noteworthy data from New Zealand show sharp increases in earthworm counts with increasing long-term use of fertilisers. This appears to be mainly through fertilisers increasing organic matter levels, as noted previously. In this context the aversion of the regenerative and organic fraternities to the use of a product such as urea is puzzling in the extreme – a cow urine patch contains massive amounts of N, with more than 80% being in the form of urea.
It is true that fertiliser placed in a band below the soil surface – as is the usual practice under row crops – may result in a reduction in some soil organisms, but these effects are temporary and are restricted to the site of the fertiliser application band.
Fertilisers produce forage and food that is lacking in nutrient value
This is a widely held view. For example, Dr Christine Jones, an Australian regenerative agriculture ‘guru’, states that the use of N fertilisers on pastures produces ‘empty grass’. Space does not allow me to deal in any detail with this aspect; however, a plethora of scientific studies have frequently reported increases in forage and food nutrient density with the use of fertilisers. In the case of pastures, for example, fertilisers have been repeatedly shown to increase forage concentrations of protein and minerals such as P, K and Zn.
And in a 2017 international review of nutrient levels in foods, Canadian scientist, Prof Robin Marles, found that the mineral nutrient composition of vegetables, fruit and grains is not declining with time, and that allegations of decline due to agricultural soil mineral depletion are unfounded.
Soil chemistry must be ‘balanced’ using the Albrecht system
The use of ‘balanced’ Ca, Mg and K ratios, as prescribed by the basic cation saturation ratio (Albrecht) model, is widely promoted in regenerative agriculture circles. I have dealt with the shortcomings of this approach repeatedly over the years, and in the interests of succinctness, let me quote the eminent New Zealand scientist, Dr Doug Edmeades: “It is nonsense – it is pseudoscience. It has no scientific basis and at best results in an increase in fertiliser costs for no benefit”.
But there are farming operations that haven’t used fertilisers for years
It is true that there are farms that use minimal or even no fertilisers. Recently I was told about a successful dairy farming operation in KwaZulu-Natal that hasn’t used fertiliser for years. How is this possible?
Experience suggests that the following factors are usually involved:
- Fertiliser applications have been excessive for long periods resulting in a major build-up of nutrients in the soil – well in excess of requirements for optimum plant growth. This typically occurs on soils used for intensive vegetable production, or on pastures where animals are fed with ‘imported’ feed such as silage and hay. It is not unusual in such situations for P soil test levels to be in excess of 100 ppm, and K tests to be above 800 ppm. With levels this high, production can continue for decades without additions of fertiliser P and K.
- In pastures, legumes such as lucerne and clover are able to contribute large amounts of N for production. Furthermore, where pastures have been in place for many years, massive amounts of N are contained in the soil organic matter, and there is continuous slow release of this N for pasture growth. So, with a combination of high soil organic matter levels and a significant legume component, appreciable yields are possible with little or no N fertiliser being applied.
- Throughout Southern Africa, and particularly in the lower rainfall irrigated areas, there are soils that have large amounts of ‘slowly available’ K in their clays. These K reserves are not detected by routine soil tests, but they are often sufficient for optimum crop production over long periods of time – sometimes decades – without any need for K fertilisers.
As noted in my previous article, many farming operations in South Africa already incorporate the major tenets of regenerative agriculture, including minimum tillage, biological N fixation and the inclusion of livestock. However, the principle of ‘minimising external inputs’, while being obviously consistent with the requirement for economic sustainability, is seriously flawed when the elimination of fertiliser is implied.
Indeed, the widespread aversion to the use of fertilisers among proponents of regenerative agriculture raises serious questions regarding the long-term sustainability of the approach. As Dr Andrew McGuire of Washington State University notes: “Biodiversity, healthy soils, and their combination in regenerative agriculture can reduce, but not replace fertiliser”. – Dr Neil Miles, Soil Health
For enquiries, contact Dr Neil Miles at firstname.lastname@example.org or visit www.soilhealth.co.za.