Solving climate change by bringing CO2 down to earth (i.e. sequestering carbon) has seemed like a Utopian idea until we tested our soils this year. Most of the experts agree that Australian soils on average have less than 1% organic matter when 5% is generally regarded as an optimum level for good fertility.
The low organic level of our soils is caused by many factors apart from low rainfall and high temperatures. Firestick farming by First Nations people destroys soil biota as well as exposing soils to direct sunlight. Removal of trees by pastoralists reduces rainfall, increases soil temperature and eliminates havens for stock and wildlife to supply manure. Repeated tilling of soils to plant wheat and other cereals exposes soils to sunlight which destroys micro-organisms.
Application of quick release fertilisers might stimulate plant growth but it also kills micro-organisms on which the organic basis of long-term fertility depends. Soil carbon is created by bugs and microbes living and dying. They need 365 days of cover from perennial plants or mulches to multiply and whilst this may be difficult for farmers, it is very easy for gardeners. So we shouldn’t have been so amazed when our soil tests returned showing a six-fold improvement in 25 years, reaching between 22-26% even for our vegetable patch despite having taken 40 crops from the soil (see table below).
Twice a year, before planting, we have applied blood and bone and either compost, poultry manure or mushroom compost. After planting and seed emergence we generally spread pea straw or lucerne hay so that our continuous application of organic matter could be as high as four applications of 3.5 kilos per square metre.
The benefits are extraordinary. Our soils now hold 5-6 times as much water and yet we have never bought fertilisers. But our humus contents would be able to maintain good yields for 50 years or more.
The quickest way to solve climate change is not to change to renewable energy like solar or wind power because that just holds our CO2 atmospheric imbalance at its current level, which is already too high. The only quick solution is to bring the CO2 back to earth by growing trees or sequestering carbon in our soils.
Whilst the arguments are complex, a simplified answer is contained in the proposition that, if we could increase our organic carbon levels by 1.6% across all the planet’s cultivated lands, then that would bring so much CO2 back to earth we would be in equilibrium again.
From our experience as gardeners in a one-hectare garden this seems really quite simple and would only take 2.2 years because we have already increased our carbon levels from 4.1% in our improved garden to 24.5% in our perennial garden. That’s a 21.4% carbon increase in 25 years or 0.86% each year.
Dr. Christine Jones, agronomist, estimates that for every 1% increase in organic soil content we conserve 14.4 litres of water per metre. Our vegetable garden needs 1,200 litres per metre to grow fruit and vegetables, of which 570 litres (48%) is supplementary water needed from November to April. By raising the soil carbon level in our vegetable garden from 4.1% to 21.8% we have potentially saved 255 litres (14.4 litres x 17.7% organic content) – some 45% of surplus needs.
