Report Synopsis

Improving Soil Health with Manure and Cover Crops

Grant Pontifex

Currently, most agricultural soils do not have the capacity to sustain continuous cropping and high yield production, without depending on expensive synthetic inputs. Agricultural practices have become simplified with large scale mono-cropping and very little diversity in rotations being common. The main reason for this study was to investigate how to improve soil health, water holding capacity and water use efficiency with manure and crop diversity. This is important for all producers, to enable ongoing profitability amidst declining terms of trade in agriculture. The major findings of this study indicate that soils need more carbon. A cropping system that creates a favourable soil habitat for microbes, that includes opportunist cover crops maximising photosynthesis, is the key to building carbon and building healthy soil. Cash crop residues alone, especially legumes will not significantly build carbon.

In addition, the supply of water and nutrients to plants is biologically driven, and as such, increasing water holding capacity and water use efficiency of soils requires more carbon and more soil biota. Soil microbes create soil aggregation and cycle nutrients, which allows more water to be stored in the soil and more nutrient availability to plants.

Grain producers need a better understanding of how the soil food web functions, and continued investigation is necessary into what impacts current farming practices, including the use of synthetic fertilisers, herbicides, fungicides, seed dressings and insecticides are having on the soil food web.

Soil cover is critical to soil health and improving water use efficiency. Protecting the soil with residue and living plants provides food for microbes and helps reduce evaporation, soil temperature and erosion.

Manure and compost are beneficial additions to soil, significantly less harmful to soil biota than synthetic fertilisers, and can improve the water holding capacity and structure of soils. However, their addition alone will not significantly increase soil organic carbon. Manure, when spread in a no-tillage system is best applied into a living cover crop in cool weather for maximum nitrogen use efficiency.

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