Why crop raised beds?
Substantial increases in grain production have been achieved in a wide range of soil types in the south west of Western Australia. These sites ranged from Beverley to Esperance, and included waterlogged soils that ranged from grey loam over clay, to gravelly sand over clay, to sand over clay.
The average increase in grain yield from research sites during 1996–2001, across a range of crops (oats, wheat, peas, lupins and canola) was 0.47t/ha. These production increases occurred during drier than normal seasons.
Grower experience is that yield increases from a range of crops are most likely on sand over clay or gravelly sand over clay, and in seasons that are normal to slightly wetter than normal.
Why use no-till on raised beds?
No-till crop establishment is essential for successfully cropping raised beds and agronomy is specific for the raised beds.
No-till benefits on raised beds are:
- retention and build-up of the organic matter of roots and their associated soil organisms to stabilise weak or dispersible soil structure
- retention of the large pores created by roots and their associated organisms to enhance rapid infiltration and aeration of the root zone
- retention of the roots as ‘reinforcing rods’ to minimise or prevent subsidence of the raised beds in wet conditions
- minimal disturbance and ‘spray’ of soil during seeding; this reduces the need to reshape beds to their original height and width
- better weed control by minimising inter-row soil disturbance (and germination).
There are good reasons to occassionally have more soil disturbance at seeding:
- to control diseases like rhizoctonia bare patch, some of the septoria diseases, black spot in peas, ascochyta in faba beans and blackleg in canola
- to incorporate root-active herbicides, such as trifuralin
- to mix fertiliser with soil close to the seed and minimise the risk of ‘fertiliser toxicity’ damage to germinating seeds.
Crop management on raised beds
Raised beds are usually 1.83m (or six feet) centre to centre, with furrows 0.45m (or 18 inches) wide. These measures depend on the cropping machinery being used and the cost of any adaptations to machinery. Because of the furrows and beds, special management is needed.
Do not seed or fertilise in the furrows. Furrows are likely to be severely waterlogged or flooded during winter. Furrows may need to be regularly cleaned to control weeds and silt build-up.
Row spacing, seeding and fertiliser rate
We recommend the seed and fertiliser that would normally be applied on the furrow area be applied on the beds. This means an increased seeding and fertiliser rate on the beds if the row spacing is kept the same. The options are five rows on the beds at 26cm spacing receiving the seed and fertiliser normally supplied to seven rows at that spacing; or seven rows at 20cm spacing receiving the same amount of seed and fertiliser. These give the same yield in most situations.
Use the same rotations as for standard cropping. Because machinery tracks in the furrows, there may be difficulties for crops requiring swathing or special stubble handling.
Raised beds improve access on waterlogged sites, which improves the opportunity for mid-season fertiliser. Fertiliser should be placed precisely on the sown rows of crop on the beds, and avoided in the furrows. Fertiliser that lands in furrows is likely to be transported off-site and become a nutrient pollutant to streams and rivers.
Spraying to control weeds, diseases and insects in crops on raised beds is the same as for crops grown on normal seedbeds.
Swathing and harvesting
Using raised beds means that harvesting equipment must fit in the furrows. All mobile machinery wheel tracks must fit the furrows, otherwise they need to operate on specially-constructed access tracks, cross-drains, or at the end of the field on the headland or catch drain. Swathing is possible with some adaptations.
Reduce the build-up of stubble in the furrows. Stubble in the furrows will impede water flow, creating waterlogged conditions in adjacent beds, causing the beds to subside and lose their improved infiltration and aeration properties. In large storms, furrow blockages may cause water to cover the beds and erode beds and channels.
Option to manage stubble on raised beds include:
- harvest the crop high and subsequently harvest the stubble for straw, leaving erect stubble about 5cm high
- harvest crops low, leaving erect stubble about 15cm high and using a highly efficient straw storm on the harvester to spread small pieces of straw and chaff evenly
- trail a chaff bin behind the harvester to avoid leaving a trail
- leave a harvester trail that is subsequently baled or burnt
- graze stubbles after harvesting them low.
If stubble builds up in the furrows of raised beds, clear them with a furrower, either as a separate operation or at seeding. Furrowers can be mounted on the front of a seeder bar.