Improving Soil Drainage Naturally

Improving Soil Drainage Naturally

Peter Burton

20th August 2010

Drainage is the topic uppermost in many farmers and growers minds right now.  The rainfall during the last few weeks has exceeded the ability of a number of drainage systems.

The rain has been relatively warm, sparking quite strong growth, with soil temperatures even in the coldest areas of the Bay of Plenty regularly exceeding 10°C.
An average daily soil temperature of 10°C is the temperature required for nutrient availability high enough to provide increased pasture growth.

Daily use of a 10-centimetre soil thermometer is an excellent way of tracking soil temperatures and accurately predicting the increase in growth rates looked forward to at this time of the year.

It is common knowledge that spring growth following a dry and frosty winter is stronger than growth following a warm wet winter. 
One of the reasons for this is the amount of moisture held in the soil with soils containing the most moisture being the slowest to warm sufficiently for the 50kgDM/ha/day pasture growth required to meet demand on most intensive dairy farms.

Frosty nights and early mornings are normally followed by bright sunny days.  Water freezing in the top of the soil cracks the soil allowing moisture to both drain and evaporate hence the rapid warming and strong growth as daylight hours increase.

In the early days of pasture development heavy treading by stock was often regarded as beneficial.  After many years of intensive stocking many soils are now compacted to the point where water ponds on the surface and drains only very slowly.
Often this may be quite close to drains however excess water is not draining down through the soil due often to lack of gaps between soil particles and groups of soil particles big enough to allow rapid percolation.

Coarse sandy soils will allow moisture to drain more rapidly than soils with finer silt and clay particles, and even where ponding doesn’t exist soils may still become anaerobic with resultant very slow pasture growth. 

Perhaps the easiest way to check for long-term anaerobic conditions is to dig a hole and look for soil mottles.  Mottles develop as various shades of orange and grey due to varying degrees of oxidation and reduction of Fe and Mn.  As oxygen depletion increases, orange, and ultimately grey mottles predominate.  The abundance of grey mottles indicates the soil is poorly drained and poorly aerated for a significant part of the year.

Poorly drained and oxygenated soils provide significantly less total pasture growth of measurably lower energy and nutritive value.  Often mechanical rippers have been used to break up these areas only to find that the same conditions prevail within a short period of time.

The integration of DoloZest and CalciZest into fertiliser programmes rapidly improves physical soil structures increasing pore space big enough for rapid water percolation.

Hard iron pan soils regarded as impermeable have become relatively free draining within two years of the initial application, providing increased pasture growth with the grazing of heavy cattle causing significantly less damage.