Crop rotation, seaweed extracts, lime, and a range of organic materials can all improve soil health and crop yields. Professor Geoff Dixon shows you several ways to improve your soil.
Rapidly rising costs of living are affecting all aspects of life. Increasing costs of fertilisers are affecting food production, both commercially and in gardens and allotments.
Wholesale prices of fertilisers have jumped four-fold from £250 to £1,000 per tonne within six months. All forms of garden fertilisers are now much more expensive. Crops, especially vegetables, only thrive if provided with adequate nutrition (see nitrogen-deficient lettuce below). Consequently, fertiliser use must become more efficient.
Nitrogen deficiency in lettuce.
Healthy, fertile soils achieved through good management are key to this process. That ensures roots can take up the nutrients needed in quantities that result in balanced, healthy growth.
Soil pH is a major regulator of nutrient availability for roots. Between pH 6.5 to 7.5, the macro nutrients, nitrogen, phosphorus, and potassium are fully available for root uptake. Below and above these values, nutrient absorption becomes less efficient.
>> How much soil cultivation do you need for your vegetables? Find out more in Prof Dixon's blog on cultivation.
As a result, soluble nutrients are wasted and washed by rainfall below the root zones. Acidic soils can be improved by liming in the autumn. Sources of lime derived from crushed limestone require up to six months to cause changes in soil pH values. Lime should be used in ornamental gardens with caution as it can result in micronutrient deficiencies.
Iron deficiency in wisteria.
Soil health and fertility are greatly increased by adding organic materials such as farmyard manure and well-made composts. Increasing soil carbon content helps mitigate climate change while raising fertiliser use efficiencies.
Beneficial soil biological life such as earthworms, insects, benign bacteria and fungi are greatly encouraged when you increase soil humus content. Using crop rotations, which include legumes, raises natural levels of soil nitrogen. This is a result of legumes’ symbiotic relationships with nitrogen-fixing bacteria.
Leafy vegetables such as brassicas require large amounts of nitrogen and, hence, should follow legumes in a rotation. Avoiding soil compaction encourages adequate aeration, benefiting root respiration and providing oxygen for other organisms.
Organic materials are of great value in ornamental gardens when applied as top dressings in late autumn or early spring. This provides two benefits: a slow release of nutrients into the root zones as decomposition occurs, and prevention of weed growth.
Inorganic fertiliser use can be further minimised by using proprietary seaweed extracts. These contain macro- and micro-nutrients plus several natural biostimulant compounds that aid healthy ornamental plant growth and flowering (illustration no 3 rose Frűhlingsgold).
Written by Professor Geoff Dixon, author of Garden practices and their science.
We begin our new series breaking down key innovations in agriculture with the Haber-Bosch process, which enabled large-scale agriculture worldwide.
Ammonia – a compound of nitrogen and hydrogen – is therefore a key ingredient in fertilisers, allowing farmers to replenish the soil with nitrogen at will. As well as fertilisers, ammonia is used in pharmaceuticals, plastics, refrigerants, explosives, and in numerous industrial processes.
But how is it made? At the turn of the 20th Century, ammonia was mostly mined from deposits of niter (also known as saltpetre – the mineral form of potassium nitrate), but the known reserves would not satisfy predicted demands. Researchers had to find alternative sources.
Fritz Haber (left) and Carl Bosch (right) created and commercialised the process.
Atmospheric nitrogen, which makes up almost 80% of air, was the obvious feedstock – its supply, to all intents and purposes, being infinite. But reacting atmospheric nitrogen, which is exceptionally stable owing to its strong triple bonds, posed a challenge for chemists globally.
In 1905, German chemist Fritz Haber cracked the riddle of fixing nitrogen from air. Using high pressure and an iron catalyst, Haber was able to directly react nitrogen and hydrogen gas to create liquid ammonia.
His process was soon scaled up by BASF chemist and engineer Carl Bosch, becoming known as the Haber-Bosch process, and this would lead to the mass production of agricultural fertilisers and a phenomenal increase in the growth of crops for human consumption.
The Haber-Bosch process is conducted at a high pressure of 200 atmospheres and reaction temperatures of 450°C. It also requires a large feedstock of natural gas, and there is a global research and development effort to replace the process with a more sustainable alternative – just as the Haber-Bosch process replaced niter mining over a century ago.