One of my young clients, who holds a degree in agriculture, recently told me – very excitedly – about how dramatically his Eragrostis had responded to lime. He wanted to know how lime had brought about this remarkable improvement in the growth of the grass. Before proceeding, a brief explanation of how lime works is called for.
Standard agricultural lime is composed of calcium and magnesium carbonates. When applied to the soil, the carbonate reacts with soil acids and neutralises them, releasing calcium and magnesium. You could say lime is the ‘antacid of the soil stomach’! Academic soil scientists – those who study and teach soil fertility from the limited perspective of inorganic chemistry – will be quick to explain that liming increases soil pH (reduces soil acidity) and this sets a number of macro- and micro-nutrients free to improve grass growth.
Biological soil scientists will agree with their academic counterparts about the pH explanation for increased grass productivity, but they’ll dig deeper. Prof William Albrecht was one such scientist. He was convinced that both calcium and magnesium are directly involved in improving plant production.
In trials conducted on calcium-deficient soils, he found that adding calcium to the soil increased the productivity of the pasture and of the animals that ingested it. I don’t know if Prof Albrecht ever gave an in-depth plant physiology explanation of how calcium increases plant production – the truth is, I haven’t yet waded through the massive number of papers he wrote.
I have, however, come across a highly plausible explanation given by Andre Voison, the great French pasture scientist. In fact, it could be said that Voison was the Albrecht of France, despite the fact that these two great scientists did not fully agree with each other.
In Soil, Grass & Cancer, published by Acres USA, Voison reveals that the tryptophan content of grass is much higher when soil calcium is adequate than when it’s low. Moreover, when phosphorus is combined with calcium, the tryptophan level is virtually doubled.
What’s the importance of this? First of all, tryptophan is an essential amino acid, one that farm animals must get from their forage, because their cells, unlike those of plants, cannot produce it. And, as most readers will know, amino acids are the building blocks of protein in plants and animals.
Tryptophan and indole-acetic acid, which is a primary plant growth hormone, have almost identical molecular structures, and thus indole-acetic acid can be derived from tryptophan. This is one good biological explanation of why liming improves grass production – soils high in calcium produce higher levels of the all-important plant growth hormone. Finally, a word of caution – applying too much lime will reduce grass production.
John Fair is a leading expert on pastures and founder and head of the SA Biofarm Institute in Harrismith. Contact John on 058 622 3585 or at [email protected]. Please state ‘Biological farming’ in the subject line of your email.