The good stuff is down there

Pasture plots looked at soils mixed to a shallow or deep level.

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 0.8m to 1.8m deep. The effectiveness of these "soil-flipping" techniques is being measured by a pasture cutting experiment.

Pasture plots looked at soils mixed to a shallow or deep level.

The study is finding out if old, buried soils grow more grass.

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," Adam says. "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/ha /year.

"Soil flipping is not irrigation. There are still limitations to pasture production and survival in extreme dry conditions."

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.

Adam says each plot was cut and weighed to identify pasture production per hectare per 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 two to four tonnes 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."

FINANCIAL COST

Costs vary according to procedure, but the spray-out, digger, levelling, cultivation, re-grassing and fertility reinstatement cost around $3500 to 5500/ha.

In the first year returns were up to 40 per cent 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 ravaged pastures.

A third year should show whether the differences reappear when growth conditions return to normal. The final cuts will be taken in August with results expected late this year.