with Brett Petersen
Kiwi Fertiliser & Golden Bay Dolomite
In 1983 Massey University research suggested 1.8m tonnes of lime were required on New Zealand soils each year. Just 1.3m tonnes are applied annually. Lime tonnage has not increased since 1981, while applications of other nutrients have increased markedly.
Between 1983 and 2007 the total nitrogen and phosphorus fertilisers applied went from 913,724 tonnes to 1,885,774 tonnes, doubling in 24 years. In 2017, urea tonnage went to 820,000, doubling in a few years. That is 345,000kg of nitrogen from urea alone. This much nitrogen requires about 700,000 tonnes of lime to counter the increase in acidity, as nitrogen strips calcium from the soil. That makes the total annual shortfall 700,000 tonnes of calcium or the equivalent approaching 2m tonnes of lime.
Sources of calcium other than lime include Dolomite and various phosphate products. Dolomite is a favoured product that contains necessary magnesium that will be depressed if calcium is applied without it. Acidic phosphates are not conducive to good microbial life, particularly fungi. One of fungi’s functions is to hold calcium in the soil. Without fungi, 98-100 per cent of added calcium can be lost.
Unfortunately, NZ authorities don’t acknowledge the difference between calcium in soil and the availability or not of calcium to plants. If calcium was considered deficient, the chances are agricultural lime may be applied in a bid to correct the levels. If the pH was satisfactory, then lime may not be applied at all.
The reality is quite different. You may not need to apply large amounts of lime, but you do need to apply calcium, not necessarily as lime.
The results may not be instant. They may take several years, but if the biology in the soil has been nurtured, the results can be in excess of any application you will have made. Some soil test calcium figures have multiplied by nine times the starting figure with modest inputs of calcium during a five-year period. The key is the biology. With salt fertilisers having a negative effect on soil microbes, most NZ farms will not capture the full benefit of lime applied in the traditional way; more so if boron is not added, but more on that later.
Dr William Albrecht, of the USA, demonstrated the effect of calcium versus pH, when he drilled soybeans with equal amounts of calcium as calcium hydroxide (alkaline), calcium nitrate (neutral) or calcium chloride (acidic). The crop yields were the same independent of pH. For example, the results were superior to soybeans grown without calcium.
Do not confuse the terms calcium, lime and pH. The primary objective of food production is to produce profitable nutrient-dense food for human consumption. Even with satisfactory pH, calcium needs to be supplied for microbe and plant health. In the short term, improving calcium levels in the soil to 68 per cent of the base saturation, on a PAL soil test, will result in better crop and animal health, quality and production. Medium term, the application of less fertiliser and nitrogen, can result. Think of calcium as an important fertiliser and not as something we periodically add to regulate soil pH which is a measurement of hydrogen.