More Efficient Use Of Nitrogen

Press, Volume CIV, Issue 30937, 18 December 1965, Page 9

More Efficient Use Of Nitrogen

It was possible that gains to be made in more efficient management of nitrogen would be the turning point in the swing from controlled grazing to zero grazing for concentrated livestock populations, Dr. K. F. O’Connor, officer-in-charge of the Lincoln substation of the Grasslands Division of the Department of Scientific and Industrial Research, said in Christchurch this week. Dr. O’Connor has just returned from Canada where he has been working in the microbiology department at the University of Guelph furthering studies initiated by himself and Dr. John Robinson, of the University of Guelph, who some three years ago completed his doctorate of philosopy in soil microbiology at Lincoln College. Their work in New Zealand in the Craigieburn soils of the Broken river catchment of the tussock grasslands involved nitrification—the conversion of ammonium nitrogen to nitrate nitrogen in the soil.

As a result of further studies in Canada using soils collected in the United States and Southern Chile as well as Canada, Dr. O’Connor said that nitrification was at a low level in undisturbed vegetation where grasses competed for ammonium nitrogen, but it reached high proportions where the vigour of the grasses was reduced and consequently their ammonium uptake. It appeared that one of the main functions of nitrification was to make nitrogen mobile in the soil so that it could be leached from soilplant systems where it was not being fully used.

in studies which bad been made in pastures in the Waikato many years ago scientists had found that nitrate was abundant in cow urine patches some days after urination had occurred. Since these patches involved concentrated application of the equivalent of up to 6001 b of nitrogen to the acre these patches were the sites of great nitrogen wastage. With

the high stocking rates practised more recently it was possible for these patches to be sufficiently numerous so that there were not large areas of nitrogen deficiency in a paddock, but at the same time as long as these amounts of urine and related nitrogen compounds were applied at such a high concentration from the grazing animal it seemed inevitable that there would still be large-scale nitrogen wastage. Because of the reliance placed in New Zealand on pasture legumes for nitrogen fixation New Zealanders might be tempted to think that they could afford such

large-scale nitrogen wastage, but two factors indicated that New Zealand would pay for this wastage. One was the risk of water pollution resulting from nitrate nitrogen in ground water making well water unsuitable for drinking, and this water finding its way into streams and rivers causing growth of vegetation there and creating a habitat unsuitable for fish. In the second place New Zealanders were almost deliberately foregoing the use of tall grasses in their pastoral agriculture so as not to injure the light-demanding, low-growing legumes such as white clover, on which at present the pastoral economy was based. Tall growing grass systems might be more efficient in use of light and water, and it would be a pity if this country neglected their use and adaptation to our pastoral production programme for the sake of preserving the present pasture—legume pattern. Dr. O’Connor said he was not recommending a switch to use of fertiliser nitrogen, but he was suggesting that if the return of nitrogen from livestock was managed so that it was less wasteful then it might be possible to use tall grasses with the high nitrogen supply but still at low fertiliser cost

Short of plastic surgery to modify the bovine anatomy and physiology, Dr. O’Connor said it seemed that the only way in which the cow’s urine could be efficiently distributed was either by keeping the cows on the move or to practice zero grazing and collecting the excreta and returning it to the pasture in irrigation systems. However, people did not have to wait for this to become economic before starting in the name of economy and public health to return effluents from places such as milking sheds, sheep yards, dairy factories, meat works, and sewage plants to the soil so that a measure of mineral economy was being practised.