It is well recognised that when soil conditions are not conducive to good growth, foliar fertilisation has a positive part to play in keeping up plant nutrition.
By watering the leaves with a dilute solution of small fertiliser molecules, aided with a little wetting agent, those same fertilisers can be absorbed through both the waxy cuticle and the stomata, and they will keep the plant growing when the soil is too cold, dry or toxic.
That same absorption is enhanced when it is warm and wet, the stomata are wide open, and growth is unimpeded.
However, Indian agricultural scientists have published research saying diluted cow urine is nature's best foliar fertiliser.
It not only has the big three — nitrogen; phosphate and potash, in pretty much the right ratios — but also has so many other minor organic nutrients in just the right sizes to slip through the plants' defences, even when it is so dry the cuticle has hardened to protect against desiccation.
However, modern dairying has created a more innovative and labour-saving technology use this product.
The K-Line irrigation system, and distribution over wide areas by means of low-cost automatic distribution valves to give timed applications over several different lines of irrigation pods, has allowed the dairy industry to apply its waste water out over pasture at rates as low as one millimetre per application.
Even on an intermittent rainy day, such a small amount would never hit the ground.
The problem is that dairy shed effluent is too thick with manure and too weak in urine content to be directly applied in such away.
The new kid on the block has to be ''green wash''.
Driving the backing gate with a water motor and washing down the yard with the exit water jetted out the behind the gate avoids teat contamination and means for a large herd the solids can be filtered from the water and the liquid reused two to three times per milking.
It is now green, but it is allowed by the authorities, and saves water use by two-thirds.
It concentrates the urine content by about three times, and that puts it close to 1%, and that makes cow urine the best foliar fertiliser.
On that first sunny day near the end of winter, when the air temperature gets above 10degC, the leaves are ready to percolate into action when the roots are not.
If you have no shed effluent on hand, make up some very dilute urea solution of about 1%, crank up the K-line, keep it below 2mm of application, and you will be surprised.
- Kevin Calvert is a research chemist in Invercargill