This article first appeared in The GROWER in February 2012
Growers suffered significant losses during recent heavy rain. We cannot handle the most extreme events without suffering losses. But we can do a lot to reduce impact and avoid damage from minor events.
Building resilience will help with adverse events and returning to normal operation once the event is over. Focus on soil and its ability to absorb, drain and hold together when large rain events occur. Soil must be protected and enhanced and suitable drainage designed and installed. Managing traffic, reducing cultivation and managing water movement are critical.
Water needs to be absorbed into the soil and allowed to drain through it. The amount absorbed depends on the soil’s infiltration rate and the time that water stays in one place. Well-structured soil has good porosity, which maximises infiltration and drainage.
Compaction means soil damage: soil is deformed forming solid layers with little or no porosity. Water cannot get through these layers fast enough, so builds up in the soil above, drowning plants and weakening soil aggregates.
The common solution is cultivation; ripping soil to break up wheel track compaction. This is expensive and self-defeating as cultivation further weakens the soil and makes future traffic even more damaging.
About 80% of all compaction happens with the first pass, so keep traffic off paddocks in the first place or keep it to defined “roads” as much as possible. Then there is little if any need to cultivate.
While we need to drive on paddocks to plant and harvest crops, we can control essential traffic and keep the rest away. LandWISE farmers have shown clearly that controlled traffic and permanent bed systems reduce equipment needs, save fuel and labour, reduce time to next crop and enhance soil quality. Win, win, win, win and win.
Water runs downhill. Even seemingly flat paddocks have high and low points. If the infiltration rate is too low, water runs to low spots where it ponds. Slowing water down with surface residues or by ground shaping keeps it in place long enough to soak in and avoid ponding and erosion. Lots of micro-dams hold rain where it falls, and slow any rivulets that may form.
HortNZ’s SFF Holding it Together project showed the benefits of furrow dyking that slows water in wheel tracks, giving it time to soak in rather than pond in low areas. This reduces soil erosion and protects crops against flooding and drowning. To sport nuts: “stop, trap, control the ball”!
Once controlled, pass it in a timely fashion. Consider artificial drainage if the soil cannot drain fast enough. Mole and tile drains provide extra flow capacity through the soil. Open drains provide a controlled way to take water to a safe disposal point.
A number of innovative drainage options are available. Old ideas linked to new GPS and computer mapping have revolutionised tile laying, surface drainage planning and ground contouring. Each has its place.
Precision tile-laying maps paddocks with GPS. It automatically surveys elevations while the tractor drives along the next tile line, calculates the depths and grades required, and precisely controls tile laying depth. It is fast and cheap compared to old practices.
Surface drainage planning controls water movement across the surface. It aims to remove excess water safely before it waterlogs the soil, by ensuring a path without ponding areas. New technology allows very detailed surveys and planning, and results in minimal soil movement for optimum drainage.
In extreme cases, surface levelling changes the whole paddock contour, directing water to safe boundaries. Because it typically moves a large volume of soil it is expensive and can have a significant soil impact. But it has other advantages such as avoiding high, dry spots and ensuring even depth to water table.
We often think of water management as irrigation, especially in summer. But we must have our soils and drainage in good order at all times of the year.
Dan Bloomer – LandWISE