I personally believe the non-application of boron on many farms is costing farmers dearly in the areas of stock health and poor pasture production, particularly from clovers. Although there is debate over the primary function of boron in plants, it is known that boron deficiency reduces the ability of root cells to absorb phosphorus, chlorine and rubidium (used to mimic potassium). This will result in stunted clovers, not only above the soil, but also below as far as the root mass is concerned, thus reducing the plants’ ability to exploit the soil.
Responses to boron become most marked when all the other elements are in good supply. Farms which have regularly received good applications of lime and potassic super, yet on which pasture growth is not really firing, could well benefit from boron. A pot trial at Ruakura showed production responses to boron on a boron deficient soil near Taupo in red clover of up to 107% increase, 74% in lucerne and 43% increase in white clover (NZ Journal of Agricultural Research 1983, p. 197-203).
Boron has also been associated with calcium deficiency in plants and animals. Boron appears to be a catalyst for the absorption and transport of calcium. When cows go down with milk fever, Calcium Boroglucanate (calcium, boron and glucose) is often used as a remedy, and this contains 4% Boric Acid (soluble boron). On one of the Caribbean islands, the high incidence of arthritis was attributed to a very low boron status in the soil. Interestingly enough, New Zealanders also have one of the highest incidences of arthritis in the world. In apple trees, bitter pit, which is caused by a low calcium level, has been corrected through boron applications. Low calcium levels in pasture plants can sometimes be attributed to the low levels of boron, even though the calcium level is good in the soil.
Boron deficiency has also been linked to poor seed and flower formation in grasses and clovers. In another pot trial at Ruakura in 1983, the affect of boron on seed production from red and white clover cultivars and lucerne was tested on a known boron deficient soil. The results were that seed production was multiplied many times with the addition of boron. In red clovers and lucerne, this was caused by a big increase in flower numbers, whereas for white clovers the increase was in the number of seeds per flower (NZ Journal of Experimental Agriculture 1983). This increase in seed production can be very significant for permanent pasture where a lot of natural reseeding takes place.
Boron can also give plants increased resistance to pests and disease. Clover flea tolerance in clovers is greater when boron levels are righted in the soil. In some crops, there is less tolerance to frosts on boron deficient soils. In Canada, field trials showed the application of boron increased drought tolerance in pasture plants. In ryegrasses, boron may lower the infection of smut and ergot in the seed head, thus reducing the incidence of ryegrass staggers.
Liming reduces the availability of boron in soils, a feature which boron has in common with most other trace elements (molybdenum and selenium being exceptions).
Plants have different requirements for boron. Boron tolerance levels, and toxicity vary considerably from species to species. Crops such as asparagus, brassicas and clovers have high requirements for boron, whereas grasses, wheat and barley have relatively low requirements. Some kiwifruit orchardists who have liberally applied boron have run into trouble with splitting vines. What is most important is that boron is applied only when either a soil test or herbage test shows it to be lacking. If soil test levels for boron are below 0.8 ppm or a clover leaf test is below 18 ppm, then a response to boron is likely. The amount of boron to apply should be determined by the severity of the deficiency and the form of boron used.
My soil science lecturer as a student at Lincoln University, the late Prof Walker, maintained that boron deficiencies were widespread in the North Island. Even back in 1974, the Annual Report of the Ministry of Agriculture recorded field trials applying 9 kg/ha of boron fertiliser, gave total pasture dry-matter production increases from 10 to 30 percent. In these trials it was noted that clover growth increased significantly, particularly in periods of high rainfall. All of this begs the question why boron is so often ignored by so many in the fertiliser industry today?
For further information, please contact ROBIN BOOM – CPAg, Member of the Institute of Professional Soil Scientists on 021-2684615.