Q&A

DEAR NEW FARM:

Here in the UK, organic yields are widely thought to be about two thirds those of conventional yields, due mostly to traditionally perfect environments for chemical farming. That environment is now less reliable, so your trials become very interesting. As a horticulture student now working on the soil science module of my course, I have been reading books on soil science and have found that these books are not about organics, nor are not overly concerned about the practical application of their contents. What's striking is how, without knowing it, they support organic growing methods.

For example, humus is shown to have the highest cation exchange capacity of all the soil colloids—most of the nitrogen in the soil is in the organic matter and soil microbes are shown to be responsible for nutrient cycling. One chapter explained buffering capacity, how available nutrients are replaced from the pool of unavailable nutrients as the available nutrients are removed by plants. Could the improvement in the yield of your organic plots be due to an increase in its buffering capacity, due to the build up of humus and organic matter? I would think of it in terms of capital and interest. To start with, you had a small amount of capital and only being able to reinvest some of the interest your capital grew slowly, but over time the rate of growth increased so that now you can harvest large crops and still have lots of fertility left in the soil for the next crop.

Samuel Eglington
United Kingdom

DEAR SAMUEL:

As you are finding out by reading your soil science book, organic farming principals are not new, and they are based on sound agronomic principals. Soil management practices that conserve and increase the soil organic matter level are beneficial to any farmer, conventional or organic. These soil management practices will improve soil health, soil structure, tilth and productivity. The improvements in the yields of our organic plots are based on the increase of soil organic matter over time. Numerous factors are improved by a small increase in soil organic matter. The buffering capacity as you mention is improved. Organic matter provides both cation-exchange and anion-exchange capacities. Organic matter stores and supplies nutrients such as nitrogen, phosphorous and sulfur, which are needed for the growth of plants and soil microorganisms.

One of the most critical plant nutrients is water. Soil organic matter increases the rate of water infiltration, reduces runoff and facilitates the penetration of plant roots. So in a dry year more of the rainfall is infiltrated into the soil and is also held by the soil organic matter for plant uptake. Nitrogen in the organic form is conserved, is slowly made available by microbial decomposition and cycling, and is not leached as easily as soluble synthetic nitrogen sources. Utilizing cover crops in our rotation is a key to conserving and building soil organic matter. Another practice is composting—when we apply compost to our soils the nutrients are available for several years, and all the crops in the rotation benefit.

NF

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