Droughts and Biology


This summer may have been a reprieve for beach lovers following the last few wet ones, but with drought declared across much of the North Island, there’s a lot of farmers hurting out there. In the Hawkes Bay we expect summer-dry conditions; but the dry and cold spring which preceded this year’s summer created the driest six months on record since 1952. The last rainfall we had in the first week of February only brought 10mm to already parched soils. What has been so interesting for me is the variation in how different farms are experiencing the conditions. It has been argued that properties using techniques which focus on soil health and soil biology are better adapted to hold on longer during dry spells and bounce back quicker when rains do come. These anecdotal stories are supported by science which shows that a focus on soil microbes and building soil carbon results in increased nutrient and water storage, and improved soil structure and resilience to climactic extremes. Soil carbon is like a giant sponge; in a loam soil a 1% increase in organic carbon (30cm depth) can increase the soils ability to store water by 144,000 litres/ha, roughly a bucket of water per m2. Research on New Zealand orchards and dairy properties have demonstrated that practices which build active soil carbon and soil biology result in marked improvements in the function and physical properties of soil. This translates to soils which make the most of every drop of water, with improved infiltration and water absorption. Soils full of biology have improved pores spaces for air and water movement, this means less compaction, deeper rooting depths, better mixing of nutrients, and less greenhouse gas emissions. One study carried out by Plant and Food Research in the Hawkes Bay showed a four-fold higher diffusion rate, meaning better aeration to roots and lower production of N20 in wet soils. With mounting concerns around water quality, practices which maximise nutrient efficiency and work with natural cycles are gaining more traction. Biologically active soils have been shown to have a positive influence on water quality through reduced nutrient losses, such as nitrogen and phosphorus and the filtering of contaminants, such as 2,4-D. Soil carbon not only assists with the water use efficiencies, but it also helps to buffer soils and plants against extremes in temperature. This was documented recently in the ability of biologically managed corn crops to maintain yields during the devastating drought crisis in the American Midwest. Estimates of the global losses of carbon from historic land use range between 66 to 200 billion tons; that’s a significant loss for a resource with such a central role in the longevity of agriculture. In New Zealand we have one of the highest losses of topsoil in the world, a shocking 11 tonnes of topsoil/ha/yr. And sure NZ has some steep and unstable landscapes, but losses are occurring beneath most farmers feet every day (see my YouTube Slaking test to see how you can easily assess this for yourself). University of Waikato research shows an average loss of around 21t/ha of soil organic carbon is occurring under NZ pastoral farms. Losses can be attributed to soil management practices, plant species, erosion, bio-cides, low biology, residue management, compaction and the inefficient use of water and nutrients. With the reductions in soil biology and soil carbon I would argue that farming is becoming increasingly vulnerable to climatic extremes. The news is not all bad however, if soil carbon can be lost on such a scale, we also have the means to rebuild it and help to make every drop count.