Silicon (Si), an element recognised as beneficial in animal nutrition, is also an important plant element, although hardly ever mentioned as such.
Adjunct associate lecturer to the School of Environmental and Rural Science at the University of New England, Peter English, has for many years believed Si is especially deficient in highly weathered acid soils, involving millions of hectares across Australian agricultural areas (about half of NSW's rural land affected).
The National Land and Water Audit identified acidity as the most serious land degradation issue facing Australian agriculture, costing $1 billion annually in lost production. Peter English's research, supported by other local and global researchers, has shown that applying Si, in a plant available form, can dramatically boost productivity of some pasture and crop species growing in these soils.
Traditionally liming light acid soils, commonly also low in available Si, has been the strategy to correct soil acidity and reduce aluminium toxicity, which tends to correlate with low pH and consequent nutrient deficiency.
However, lime is relatively immobile and tends to mainly only correct soil acidity in the top zero to 10 centimetre layer, unless applied at, for most situations, very high uneconomical rates, and thoroughly mixed through the deeper soil profile.
What English's research shows, is that relatively low rates of water-soluble Si, (mono silicic acid) improves phosphorus uptake in species like wheat, barley, clover, chickpeas and lucerne on acid low phosphorus light soils. Because water soluble Si is mobile, unlike lime, benefit to these plants is through the soil profile. Plant root mass and depth increases down the soil profile helping to develop far greater biomass and production.
University of New England research has shown that Si fertiliser, applied to crops and pastures in low Si soils can increase their use of native and applied phosphorus. Trials in Western Australia have shown 30 per cent yield increases in barley and chickpea in these soils where 25-35kg/ha Si fertiliser were applied.
Glasshouse studies have shown that lucerne, normally totally unsuited to low pH deep sandy soils, from Binnaway in central NSW, grows well when treated with water soluble Si.
English stresses that Si application does not negate the need to apply phosphorus fertiliser to crops and pastures on low phosphorus soils. But lower rates of phosphorus fertiliser are required in Si deficient soils when Si is also added to the fertiliser program.
Global interest in Si soil deficiency is documented in a number of peer-reviewed papers, including Silicon increases phosphorus uptake by wheat under low P acid soil conditions, Ljiljana Kostic et al, Plant and Soil (2017) and Agronomy for Sustainable Development journal's Silicon enhancement of estimated plant biomass carbon accumulation under abiotic and biotic stresses. A meta-analysis, Zichuan Li1 et al (2018).
This research for the first time demonstrates that in low phosphorus acid soils, improved growth and increased shoot phosphorus levels is a direct result of Si stimulating phosphorus uptake via various plant reactions.
This work also showed the indirect effect of applied Si on alleviation of aluminium toxicity was more effective than liming by requiring lower rates of product. Also, the in-plant effect of Si addition far improves phosphorus uptake compared to lime application.
Research indicates that the main markets for Si fertiliser is on low pH and low phosphorus soils as well as soils low in available Si with plant species like wheat, barley, clover, chickpeas and lucerne.
English's research has been with a natural rock silicate that will be mined and hopefully manufactured in the New England District of NSW. It will then be mixed with starter fertiliser for cropping soils and superphosphate for pastures.
He is now seeking interest from individuals or groups to take part in product development that aims to have commercial quantities available in 2021/22. A limited quantity of granulated product has already been manufactured and is available for 2020 field trials. Email peter@peewee.net.au
Next week: New wheat varieties for 2020.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
