PW Burton
Do you realise that the amount of carbon in your soils affects how much they produce?
A very readable and informative paper on soil carbon produced by the Bay of Plenty Regional Authority in 2011 contains the following passage, “Most pastoral soils in New Zealand are generally considered to be rich in organic carbon so large increases in productivity are not expected by adding more organic matter.
However recent research has shown that in intensive lowland livestock systems (e.g. dairying) , soils have lost organic carbon by an average of 1.0 tonne carbon/ha/year over the last 20 – 30 years while in hilly land soils, organic carbon levels have increased.”
While 1.0 tonne/ha is a very small percentage of total soil held carbon each year the loss of each tonne is a greater proportion of the remainder. Think of it as compounding interest in reverse.
In the short term a small loss has little effect, however soil carbon largely dictates pasture and total farm production, and less carbon ultimately leads to lower output.
And why the difference between hilly and lowland livestock systems? There’s a school of thought that it can be directly linked to the steady increase in fertiliser nitrogen applications to flatter country, since urea from Kapuni came on stream around 1990.
Graham Shepherd the owner of Bioagrinomics, the producer of the widely used and highly respected Visual Soil Assessment wrote recently, “…our GHG emissions have doubled since 1990. Our groundwater, lakes and rivers are becoming increasingly contaminated with nitrogen and phosphorus, and soil C levels are decreasing, particularly under high-N dairying and conventional cropping regimes”.
However, not all intensive pastoral operations are suffering from a loss in soil carbon, and a correspondingly lower pasture production. The soil on a long-term Functional Fertiliser client’s property, measured in 2012, contained 22% more Total Carbon in the top 30cm than a neighbouring property, where in excess of 200kg N/ha was regularly applied.
The Functional Fertiliser client applies less than 25kgN/ha annually and, based on independent Overseer modelling, grew 19,300kgDM/ha in the 2011/12 season, 1,800kg more per hectare than the neighbouring high-N property. The small amount of N applied in autumn reduces the vigour of lower value summer grasses by stimulating rye and other cooler temperature growing species prior to winter.
Although one season provides only a snapshot in time, the 23% increase in pasture production on this farm from 15,600kg to 19,300 kgDM/ha since 2008, indicates soil carbon is steadily lifting. Pasture production to the end of April this year (2016) will be close to 21,000kgDM/ha.
The importance of soil organic matter, measured as soil carbon, is in its ability to store both nutrient and moisture. Increased nutrient storage means stronger growth throughout spring, particularly during the often troublesome November period.
Extra growth in November means better fed cows and higher in-calf rates, along with a wedge of feed allowing greater intervals between grazings to be achieved, and more feed available over the summer period.
Increased moisture holding capacity improves summer pasture growth, lessening the impact of dry weather. Not only is more moisture available for plant uptake. Organic substances can hold up to five times their own weight in water, and higher amounts of organic matter result in improved physical soil structures.
Better physical structures mean plant roots are able to penetrate further, allowing them access to moisture and nutrient from a lower depth. Which means plants grow longer into dry periods, and recover more quickly as conditions become favourable.
Winter and spring growth are also enhanced as excess moisture drains more freely and, as soils with more organic matter are darker, they absorb more solar radiation, resulting in earlier warming.
Full nutrient programmes based on DoloZest and CalciZest, the two unique soil improvers developed by Functional Fertiliser have, over 15 years of use, provided intensive dairy farmer clients with more total pasture of higher quality, spread over a twelve month period, without using year round fertiliser nitrogen. For more information call Peter on 0800 843 809.
