A profile of good soil management

Vegetable and top fruit growers from Counties Down and Armagh met recently to address issues relating to field drainage and soil structure at workshops organised by Greenmount Campus. The guest speaker was Professor Gordon Spoor, formerly Professor of Soil Physics at Silsoe College, Bedfordshire.

The morning saw Professor Spoor investigate field soils around the Comber district. The emphasis in this workshop was on digging soil profiles for clues before deciding on measures for improvement. Removing sections of the soil profile and noticing how the soil breaks down will indicate the porosity of the soil. The presence and distribution of roots provide clear indication of potential plant growth. If the soil breaks vertically under slight pressure and roots are present there is no need to undertake any action.

Where soils are ploughed to the same depth year after year a pan may develop which is impervious to water so causing poor drainage and subsequent root death. This soil will tend to break horizontally, and there will be no evidence of root penetration. In this case cultivation is necessary to break this pan. While in such situations sub soiling is useful the Professor commented that unnecessary sub-soiling, or subsoiling with poorly set machinery, disrupts the soil profile and triggers the breakdown of the established structure.

In the afternoon, Professor Spoor met with Top Fruit growers at Northern Ireland Horticulture and Plant Breeding Station, Loughgall, to discuss orchard soils with a view to improving drainage. This is a difficult issue for orchard crops, which remain in situ for several decades and whose management relies heavily on machinery usage through all seasons.

Professor Spoor proposed an alternative to the normally prohibitive cost of installing additional permanent drains in orchards, suggesting that mole ploughing in suitable soil types could become a regular part of the cultivation programme and thus provide temporary benefit for key periods of the year.

He also pointed out the adverse effect to soil condition of the herbicide strip within the orchard and discussed with growers the possibility of reducing its width and the frequency of weed control.

The growers from both sectors were made aware of problems that arise from over-cultivation of topsoil, especially where bare earth remains exposed to the elements, for example in seedbed preparation. Rainfall washes the finer soil particles into drainage (air) spaces in the soil structure, so clogging the drainage flow of water and reducing availability of oxygen to the roots. As a result, surface compaction occurs and plant growth is badly affected.

Growers should consider enhancing organic matter in their soils through recycling plant debris after harvest, or by applications of manures and mulches where feasible. Organic matter is vital to the formation of good ‘crumb’ structure and its presence helps to feed the population of earthworms, which are a key component of healthy soils. Earthworm activity forms beneficial aggregates in the soil structure and the tunnels they create are very stable, effective mini-drains for excess water. There is also evidence that plant roots can easily exploit these channels to extend through the soil.

Effective drainage of water, either surface or underground, ensures successful root development and root distribution which should improve the health status of the crop.