Soil porosity is a measure of air space in the soil and macroporosity is a measure of the proportion of large pores in the soil that provide air supply to roots and microbes. Soils that have been compacted because of animal treading or machinery have poor macroporosity levels. This is like a foot on an individual’s throat, and they are saying they can’t breathe. It’s the same scenario for plants and microbes.
Ag Research soil scientist Dr Peter Singleton and his team based at Ruakura Research centre, Hamilton, in the late 1990s found that a 10% macroporosity level in soils was a critical value in relation to pasture and crop production. It’s a useful soil physical field calibrated test developed for New Zealand soils. His research team found that there was a 10 % decrease in pasture production for every 1% decrease in macroporosity below the critical level of 10 %.
Depending on the soil type, treading and compaction damage can reduce pasture production by up to 50% or more and take 6 months to 1 year to return to normal pasture production levels. When soil structure is damaged, the infiltration rate decreases and pores that are required for aeration and drainage are destroyed.
Other issues include ~80% decrease in worm populations, increased runoff of water, sediment and faecal coliforms, reduction of phosphate and other nutrient uptake and increased greenhouse gases. It can also affect soil temperature and plant root penetration.
An excellent illustration of compaction and soil aeration was evident on a sheep and beef farm I visited near Te Kuiti. In a 30 meter by several hundred-meter strip in a paddock upon a hill, there was amazing pasture growth. This patch had approximately 2500 pasture cover but on either side of the 30 meter strip the cover would have been less than halve. The difference was obvious. The reason for the extra pasture growth was that a trench had been dug for a water pipe and when the soil had been returned it was in a less compacted state.
As another example, I advised a young dairy farmer near Putaruru to aerate his paddock with a James aerator. The soil type was volcanic silt loam. He said the difference after aerating the paddock was incredible as the pasture growth difference to the next paddock where he did not aerate was phenomenal.
There are many ways you can aerate a soil. You can do it chemically by using lime or gypsum, biologically by adding compost/organic matter, encouraging earthworms (by liming), and microbes & fungi or mechanically with a tractor and equipment such as a James aerator, ground hog, Rata and numerous other brands’ including a Forbes soil conditioner. Having drains can also reduce compaction by draining soils in wet periods of the year which will reduce compaction.
About 2 months ago I was introduced to Stu Forbes by a mutual friend. Stu had developed his Forbes soil conditioner/aerator over a 35-year period with a team, including Prof. John Baker. Stu reckons he has got the best piece of equipment to aerate soils with. But he is always challenged by ‘show me the data’. That’s where I come in, as I see soil aeration/soil structure to be just as important, as soil moisture (by rainfall or irrigation) and soil pH and nutrients.
Stu and I have therefore commenced trials on sheep/beef and dairy farms using the Forbes soil conditioner. The trial will be carried out on many farms around New Zealand, from as far north as Northland to Wairarapa, and in Canterbury. Pasture production will be monitored with and without the use of the soil conditioner.