#6 - Apr 2017 - Garden Stuff - © Sandy Lang - slang@xtra.co.nz
SOIL
April/May: Mid/late autumn. Summer crops out, winter crops in. About the only winter options are leaf veggies and broad beans. Garden centres have a good range of seedlings. Now’s a good time to think about your soil…
What is soil: When rock is exposed to the weather (cold/hot, wet/dry), it slowly crumbles to form smaller rocks. These slowly crumble to form even smaller rocks, and so on. We name these mini rocks according to size - coarse sand (0.5–1.0 mm); medium sand (0.25–0.50); fine sand (0.10–0.25 mm); very fine sand (0.05–0.10 mm); silt (0.002–0.05 mm) and clay (less than 0.002 mm). Soils are a mixture of different sizes of these mini rocks. We talk about a soil’s particle size distribution. Most Eastbourne soils are very sandy; close to the hills there may be some silt and clay particles in the mix.
But this is just the mineral part of a soil. A wholly mineral soil is no use for plants. Sand holds little water and few nutrients. Small soil particles (silt, clay) hold more water and more nutrients (good) but also become compacted (bad), so water, air and roots find it hard to move through.
Organic matter: Add rotting plant debris and a poor soil comes alive. Organic matter increases a sandy soil’s water- and mineral-holding ability and increases a clay soil’s porosity – less waterlogging, more air, easier root growth.
Biome: Organic matter also allows the soil to develop a rich biome. The various organisms of the soil biome use the organic matter as food and co-exist in a happy relationship with plant roots. Low soil organic matter means a sickly biome and sickly plants.
Low organic matter: Intensive arable farming lowers soil organic matter and reduces productivity. Adding mineral fertilisers raises productivity but the fertilisers quickly leach to the waterways. Toxic algal blooms result. Around the world, farmers are working to increase soil organic matter. It takes many years to undo the soil damage done over many years.
Total carbon: Soil organic matter is measured as total carbon. Ratings for NZ soils are: low (2-4%); medium (4-10%); high (10-20%). Many Eastbourne soils are ‘very low’ – our homes were built on sand dunes. Thanks to Armes Tree Solutions and Downer and TreeTech we get free tree-chip mulch. Use it… ___________________________________