Marlborough vineyards are overcoming sodic soil conditions by the application of compost as mulch. In this article, Wholesale Landscapes looks at the problem and investigates methods of treatment.
Sodic soils are characterised by high levels of exchangeable sodium, which impedes water infiltration and water availability, adversely affecting plant growth. Sodic soils are innately unstable, exhibiting poor physical and chemical properties. Sodicity degrades soil properties by weakening the bond between soil particles, destroying aggregation and leading to dense, cloddy and structureless soils.
Soil sodicity can lead to a reduced flow of water through soil, which can limit leaching and can cause salt to accumulate over time, developing saline subsoils. It can lead to dispersion in the soil surface, causing crusting and sealing, which then impedes water infiltration. Sodicity causes dispersion in the subsoil, accelerating erosion, which can cause the appearance of gullies and tunnels. These soils are often waterlogged in winter causing the nitrogen to leach out and yet are dry and baked hard in the summer months.
Compost is a long-term solution for sodic soils, increasing the organic matter in the soil and improving soil structure. This, in turn, improves root health and thereby reduces the incidence of root disease.
The application of compost insulates the soil and buffers soil temperature, preventing the surface from crusting in summer and protecting the roots from getting burnt. Compost can provide relief from droughts and affects drainage positively by cushioning water flow and stopping the soil from drying out. Some soils may benefit from mechanical ripping to penetrate just below the compacted soil layer before composting.
As well as its mulching effect, compost slowly releases its natural fertilisers into the soil to be accessed by the root system. Additional, specific fertilisers can be added at the time of compost spreading to maximise efficiency in vineyard management.
In terms of the timing of compost application, after harvest or once the soil has dried off sufficiently after winter, is suggested. It is ideal to have the compost down at bud burst and then to apply nitrogen on top and water it in so the vines get the spring flush. Even an autumn application can work if you want to make the most of a dry spell.
This timing is important for higher yeast assimilable nitrogen, (YAN), content at grape harvest. Low YAN is associated with low organic content in soil and overall dry growing conditions. Nitrogen uptake occurs in the late spring, after flowering. Increased organic content, from compost mulch, available at this time can have a positive effect on YAN, improving fermentation.
Overall, the application of compost is beneficial for the vigour and health of vine and root, and ultimately, grape production. Compost works in well with irrigation and fertiliser programmes to produce the maximum benefit and efficiencies for vine growth and health and its application plays a fundamental role in the whole picture of vineyard management.
Wholesale Landscapes has a wide range of composts available to incorporate into your vineyard management scheme. Please visit our website at http://www.wholesalelandscapes.co.nz/ for more information.
Wholesale Landscapes would like to thankJohn Turner of John Turner Consultancy Ltd for providing technical assistance and information.