Responding to the consequences of a wet season

Fert Options
with Robin Boom
Agronomic Advisory Services

After the wettest year for decades, many farms look yellow from the leaching out of nutrients. The major elements which have been flushed out of the soils are sulphur, potassium and nitrogen. Consequently I have recommended clients use sulphate of ammonia-based fertilisers if a nitrogen boost has been required, rather than straight urea.

Sulphur is an integral part of the amino acids methionine and cysteine which are building blocks of proteins and without enough sulphur, a lot of the nitrogen in pasture can be non-protein nitrogen which has little value to stock, causing them to scour. Although it may appear that there is a lot of grass being offered to animals, they just don’t produce all that well off it, particularly if no other supplementary feed is offered to them.

Clover base

Another observation is those properties with a good clover base in their pastures are not as yellow as those which don’t have much clover. One reason for the absence of clovers is low potassium levels, and with the high amount of rainfall, these need topping up badly on a lot of properties. Phosphorus on the other hand does not leach out on most soils in the Waikato/BOP/King Country region with the exception of raw peat soils, whereas on a lot of the gumland soils in Northland which are podzols, leaching out of phosphorus is an issue. Soil pH levels are largely unaffected by rainfall, and most of the metallic elements such as magnesium, copper, manganese, cobalt and zinc do not leach.

Low chloride

One element which has been particularly low this spring in pasture tests is chloride, which is highly leachable, and this low chloride can cause the Dietary Cation Anion Difference to increase, which increases the risk for having milk fever-related problems.

Giving cows calcium or magnesium chloride-based products can help reduce milk fever, and applying potassium chloride (muriate of potash) and salt (sodium chloride) to the soil will lift chloride levels in the pasture.

Another element prone to leaching is boron, but now there are calcium and magnesium borate products which are not subject to leaching as the old sodium borate products which are popular for cropping due to their solubility and fast-release action.

Copper availability

One element which has been higher than usual this spring in pasture analyses is molybdenum which is an important element for clover production, but when in excess it can severely restrict copper availability in livestock. Molybdenum levels fluctuate throughout the year, dropping significantly in drier months and increasing over wetter periods, which is the opposite to copper, which is higher in drier periods and drops over the wetter winter-spring period.

At the NZ Grassland Association conference held in Whanganui in November, an interesting paper was presented by Dr Pip Gerard, a Ruakura-based entomologist who found the application of lime can help protect pastures from black beetle infestations.

The Grassland Association is a great interface between scientists, farmers and extension people, with more than 900 members nationwide and has been going for 80 years.

Organisations like the NZ Grasslands Association, the NZ Society of Soil Science, and the Massey University Fertiliser and Lime Research Centre have annual conferences where good science is presented and debated. Lacking in attendance at these events are fringe fertiliser companies who I find make bogus claims and even state theirs is a scientific approach, but they never darken the doorways of these organisations’ annual conferences to learn real science.

Robin Boom, CPAg, Member of the Institute of Professional Soil Scientists. Phone 027 444 8764.

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