Nitrogen is essential for plant growth. It’s how best to ensure there is sufficient to maximise plant growth at all times.
At almost any time during the year applied synthetic N will provide an increase in growth, after a short delay.
The issue is that, based on much research, there is an almost corresponding drop in growth afterwards.
Pasture farmers have responded by applying nitrogen every few weeks to overcome this lag with a result that even under irrigation 16 tonne of dry matter/ha annually is the maximum.
That’s a significant drop from the 18 – 18.5 tonne DM/ha recorded on non-irrigated land prior to 1990 when the use of urea from Taranaki became routine.
The reason for this reduction is the loss of soil carbon, a direct result of synthetic nitrogen applications.
Soil carbon in the form of humus provides storage of both nutrient and moisture. Nitrogen and carbon are linked and synthetic nitrogen ‘burns’ carbon with a subsequent release of nitrogen available for plant uptake.
Which is why the first application provided the best response. It’s an almost imperceptible decline, usually compensated for by applying a slightly higher rate, but the reduction is measurable over time.
And it doesn’t matter whether the crop is pasture or carrots. Some years back the last of the town supply dairy farms near Gisborne was sold at a price several times greater than pastoral land normally sold for.
It was sold for crop production with the price justified by the extra production available in the first few years.
With the loss of soil carbon, the cost of production rises. Cultivation becomes more difficult, more high analysis fertiliser is required along with higher pesticide and weed control costs.
Eventually costs rise to meet income and a change in land use is necessary. Permanent grazed pasture is the ultimate end for exhausted cropping country as it is under pasture that carbon is most quickly sequestered.
Thirty years of well managed grazing and sufficient carbon will have been built back in for a short period of cropping to be viable.
Which brings us back to the very early settlers throughout the world, prior to the use of fertiliser, rotationally cropped land with a period of grazing being the cornerstone.
A reliance on synthetic nitrogen and water-soluble nutrients has allowed us to enjoy a lifestyle which we must now pay for.
The benefits of carbon in the form of humus are; increased moisture retention with land less prone to flooding, cleaner water as carbon is the ultimate filter, and a lower requirement for soluble nutrient.
There is no downside apart from maybe an increase in the price of out of season vegetables.
It is also important to acknowledge the fact that low lying highly fertile land throughout the country benefitted greatly from periodic flooding which now, due to higher stop banks, occurs less frequently.
There is always a consequence to changing natural systems, however the know how is available to benefit from unintended harm as our clover-based pastoral farming expertise is second to none.
For more information call Peter on 0274950041.
