Soil Health Series | Mineral Fertilisers

This is the final article of the Soil Health series. These series of articles are about the pillars of healthy soils and crops and the foundation of food production in modern agriculture. Each area is as important as the other and while we often focus on one or two if these pillars (often Mineral Fertilisers and Soil Structure) we neglect the others which have the result of degrading our soils and restricting performance.

Mineral Fertilisers

Often considered before any of the 3 pillars the use of fertilisers is essential for the world’s ongoing food security. The demand is going to continue to grow in the future with the surging population. The demands for larger crop yields make using fertilisers a necessity rather than a luxury.  Prior to the modern era of commercial agriculture, satisfactory yields were achievable by adding organic manures, adopting crop rotations or resting the land. With the industrialisation of agriculture the boom of crop output has been achieved by using mineral fertilisers along with improved management, crop varieties, mechanisation, irrigation and the control of disease and pests. 

The Need for Fertilisers

Every crop that’s grown removes nutrients from the soil in order to grow. Where the utilisation is higher than the input; problems can occur. For example nutrient depletion or nutrient “mining” can occur--a condition that is not sustainable in the long term. Because of this, the importance of a quality soil analysis cannot be underestimated. Its critical that a soil analysis looks at more than just the macronutrients. Nitrogen, phosphorus and potassium are often considered to be the most important elements because they are the building blocks for cells in the plants, and are needed in the greatest quantities, and so are often depleted in New Zealand soils. It is also important to look at the base saturation percentage for Calcium, Magnesium, Potassium and Sodium. This is often ignored and can lead to plant and animal health issues down the track. Plants also require micro nutrients (boron, copper, iron, cobalt, manganese, molybdenum, chlorine, iodine, selenium and zinc), these are just as important for healthy growth, but are called micro only because they are needed in smaller volumes. Globally the loss of micronutrients in soils is now becoming a serious problem as many farmers fail to replace them.

The aims of a fertiliser programme should go beyond creating the maximum dry matter production or yield of plants. It is becoming more important than ever to design a soil management and fertiliser programme that improves soil ecology and produces a healthy plant and therefore a healthy animal. Where possible we advocate the use of natural fertilisers for the simple reason that they have less impact on soil life and often even aid it.

The Role of Soil Microbes

An active soil ecosystem with beneficial soil microorganisms can have a very positive impact on fertiliser effectiveness. Microbes can solubilise compounds both organic and inorganic, that are largely unavailable to plants and make them available for uptake by the plants root system, allowing the plant to put more energy into growth. In performing this important function, the Microbes create a more efficient use of added nutrients, generating a better growth response from fertiliser inputs.  Mycorrhizae can dramatically affect how much P fertiliser is required as with a healthy mycorrhizae presence in the soil more P will be provided to the plants, therefore require less to be added.

Application of ammonia based fertilisers can adversely affect soil health by depleting humus and soil organic matter, and creating unfavourable conditions for microbes to grow and function. However, the effect is dependent on the form and amount of fertilizer N applied, the soil’s buffering capacity, and soil management practices such as liming. In terms of effects on soil health and microbial activity improvements are still possible when organic matter and bio stimulants are applied alongside a mineral fertiliser program to meet the nutrient requirements of the crops but also feed the engine room of the soil.  It is important for every farmer to consider the crops need alongside the effect on your soil when developing a fertiliser program. 

As important as your fertiliser program is I hope that you now understand that the other 3 pillars, microbes, soil structure and building humus are equally important. I also hope that you have learned something new that you will be able to implement in your garden, farm or orchard. If you have any questions please contact us