To bring the older, better soils back to the surface, farmers are now using diggers to mix or turn the soil profile completely upside down, from 0.8-1.8m deep. The effectiveness of these ‘soil-flipping’ techniques is being measured by a pasture cutting experiment.
DairyTeam farm consultant Bill Adam says a three-year DairyNZ-funded study is designed to test whether old, buried soils grow more grass.
“Farmers in the area noticed where they mixed topsoil with subsoil, that pasture would always grow better during dry conditions,” says Bill. “Otherwise they’re dealing with coarse, challenging summer-dry topsoils.”
The study confirmed that the biggest difference in pasture production from soil flipping is when the soil is drying out (heading into a dry spell), giving desirable pasture species better chance of survival. The advantage may be up to 4 tonne/h /year.
“Soil flipping is not irrigation – there are still limitations to pasture production and survival in extreme dry conditions,” says Bill.
Study evaluates soils
Thirty plots were placed on two sites to find out if soils should be mixed to a shallow or deep level, and whether to put topsoil back on top or to mix the whole soil profile.
Bill says each plot was cut and weighed to identify pasture production/ha/year.
“Reinstating soil fertility was surprisingly easy – very little capital fertiliser was required above normal maintenance. pH and Olsen P levels were lower on flipped soils, but natural potassium (K) and sulphur (S) levels were generally higher.”
In the first year – a drought year – all flipped soils grew more than unflipped (unchanged) soils, by 2-4 tonne DM/ha.
The second year (another drought) again saw the flipped plots grow more than the unflipped, but in some instances by a non-significant margin. “Two consecutive years of drought proved too much for one of the experimental sites, which needed to be re-sown.”
Costs vary according to procedure, but the spray-out, digger, levelling, cultivation, regrassing and fertility reinstatement cost around $3500-$5500/ha.
In the first year, returns were up to 40 percent of the capital outlay and the best flipping procedures looked to be on track for a two-and-a-half year payback of the initial cost. However, second year results were less impressive as a second drought
A third year should show whether the differences reappear when growth conditions return to normal. The final cuts will be taken in August 2015, with results due by late 2015.
This project is funded thorugh the DairyNZ On-Farm innovation Fund.
This article was originally published in Inside Dairy February 2015