Even though it’s combating erosion problems, reducing water evaporation and helping to keep soil cool, minimum tillage is failing to live up to expectations in many countries, says HF de Wet, a South African soil consultant currently working in Australia. “First, it hasn’t resulted in a significant rise in organic matter in the soil,” he explains. “This is because stubble needs to be incorporated into the soil to build soil organic matter.
Farmers using minimum tillage, however, leave the stubble on top of the soil.” Minimum tillage also hasn’t resulted in a major reduction in production costs. As a matter of fact, in some cases it’s even increased costs by creating new production challenges. For example, some farmers experience increased herbicide resistance because minimum tillage reduces the non-chemical options available to control weed problems, and farmers can’t burn or plough lands to get rid of weeds. Most also refrain from sending sheep or cattle to graze lands after harvesting, and thus reduce the weed seed bank, because of fears they’ll compact the soil.
While minimum tillage will remain an important production tool due to its ability to help prevent erosion, many Australian farmers are now incorporating biological farming methods into their production. Increasingly, these farmers are observing the way biological farming methods help improve soil quality and health, says De Wet.
Optimal nutrient uptake
With biological farming, instead of simply feeding the soil by adding more and more fertiliser, producers aim to create optimal soil conditions for nutrient uptake by using more natural products, such as rock phosphate, calcium or potassium silicon; by stimulating soil biology and by balancing soil elements. The idea is that by building a healthy soil, you’ll produce a healthy plant. De Wet explains the Australian government also offers farmers various incentives to increase the organic matter in their soil, due to rising concerns of global warming.
Farmers using biological production methods are also less dependent on chemical pesticides for weed and disease control. Experiments De Wet has conducted in Australia have obtained positive results using mineral fertilisation. During planting he applied Western Mineral Fertiliser, a mixture of rock phosphate, dolomite, calcium, silicate and microelements in sulphates. This increased phosphate uptake by almost 21%, compared to cases using the chemical fertilisers monoammonium phosphate (MAP) and diammonium phosphate (DAP).
From 1992 to 1996, De Wet conducted research at the Agricultural Research Council’s Small Grain Institute on the conversion of nitrogen, including soil mineralisation and nitrification.
His research shows that organic carbon and nitrogen, clay, cation exchange capacity (CEC) and pH are the main factors influencing soil mineralisation and nitrification. If any of these are out of balance, it can “lock up” other elements in the soil, preventing them from becoming available for plant absorption. De Wet later added soil temperature, soil moisture level and the fungi : bacteria ratio to this list.
“For example, if nitrogen is applied to cold or wet soils, very little of it would become available to the soil or plants, due to the anaerobic conditions associated with waterlogging,” he explains.
De Wet stresses that the fungi : bacterial ratio varies at different stages of plant growth. This is important, as specific bacteria and fungi are responsible for breaking down specific nutrients and making them available to other soil organisms or plants.
More roots, more wheat
Root development contributes up to 80% of the organic carbon in the soil. Plants with larger root systems absorb soil nutrients and moisture more effectively. De Wet’s recent research therefore investigates factors that influence root development. In the first study he applied 80kg/ha of MAP and 25â„“/ha of urea ammonium phosphate when growing wheat. In one sample he added 5â„“/ha of a calcium supplement. A control sample receive no additional supplements.
In the calcium-supplemented sample, the wheat’s root surface area was almost five times larger than in the control sample. Plant sap analysis also revealed that the wheat that received calcium, absorbed three times more phosphate.
However, the most important result was attained in terms of yield – the calcium-treated sample produced a yield of 2 781kg/ha, compared with the control’s 2 541kg/ha. Based on the wheat price, the increased production translated into an additional A,20 (R700,41).
The fungus factor
Another of De Wet’s Australian studies evaluated the impact of trichoderma – a type of soil fungi – on soil bacterial and fungal activity. Four treatments were applied. In the first sample, seed was inoculated with trichoderma. In the control sample seed received no treatment.
The third sample received liquid trichoderma, and the fourth sample a fungicide called Impact, both applied at planting. Seed inoculated with trichoderma yielded 80kg/ha less wheat than the control sample, at 1 450kg/ha. This translated into a loss of A/ha (R183,93/ha). The fungicide treatment destroyed all fungi in the soil – irrespective of whether these were beneficial and harmful – and yield was 60kg/ha less wheat than the control. Factoring in the increased cost of this treatment, this translated into a loss of A/ha (R191,28/ha).
Finally, applying liquid trichoderma gave the best results in terms of yield and economy. Yield was 100kg higher than the control, and profit increased by A/ha (R161,86/ha).
E-mail HF de Wet at [email protected] |fw