Robin Boom Agronomic Advisory Services

It’s that time of year for me – taking samples for maize-growing clients, including several who have award-winning crops in the Waikato and Bay of Plenty region.

Maize is one hungry plant for nutrients and if you don’t feed the soil right you can really compromise production. Therefore, it is imperative to find out what is lacking by soil testing.

But I find myself in constant despair about how much poor knowledge there is in being able to grow decent maize crops. Unless there is a drought, you should be able to expect a maize silage crop of at least 25 tonnes DM/ha.

Recently, I visited a maize contactor using one of the fertiliser co-op representatives to do their soil tests; and their ‘agronomist’ was telling me he likes to get a calcium base saturation percentage to 60 per cent.

This was based on a test result from a Waikato-based laboratory, and while this rule of thumb may work on higher Cation Exchange Capacity soils it would be unwise on low CEC soils or else over-liming can be an issue as the soil can become calcified, creating magnesium and potassium deficiencies.

During the years I’ve run into people who’ve read professor William Albrecht’s books and research and try to aim for his ratios.

But do this using a New Zealand laboratory that uses CEC methodology, which buffers the soil to a pH of 7 in the lab, compared to Total Exchange Capacity that uses the field pH of the soil which American labs do.

This includes Brookside Laboratories, the original Albrecht lab in Ohio, which is my lab of choice. Albrecht ratios should not be considered if using a local laboratory with different testing methodology.

Manganese deficiency

The other issue I have with these local soil tests is they normally only consider six or seven elements, yet plants need 16 to grow properly. Elements such as boron and zinc are critical for maize, and over-liming peat soils in particular can cause manganese deficiency.

Maize is very hungry for potassium and I sometimes meet farmers who go to the effort and expense of spraying out and working up paddocks properly and buying the seed, yet do not apply enough fertiliser nutrients.

Here I also blame some of the historical recommendations put out by some of the maize seed companies, who like to trim back fertiliser inputs, thinking it an unnecessary cost.

Some soils are naturally high in potassium; and if effluent paddocks are being used to grow maize there is probably little need for additional potassium, but always refer to soil test figures before leaving potassium out of the base fertiliser dressing.

Potassium Chloride

On low potassium soils up to 800kg/ha of potassium chloride can be applied as part of the base fertiliser dressing. Phosphorus is another nutrient that should not be compromised, particularly on volcanic ash soils.

Another forgotten element is carbon, or organic matter in the soil. This determines the nutrient and moisture holding capacity in the soil and is also what soil organisms thrive on. On continuous maize ground, organic matter levels become depleted over time and applying animal manures such as cowshed effluent, feed-pad waste, chicken manure, goat manure, horse manure or compost materials will be beneficial.

If using composts, try not to get ones which are full of woody plant material and twigs. Go for ones with more leafy material where the carbon to nitrogen ratio is no more than about 18:1.

Snake oil

Maize is also a target for “snake oil” products. I recall about 15 years ago a maize client wanted to try a particular product, which someone he knew had become a rep for, which cost a lot of money for very little nutrient.

Their claim was that their particular product would release all of the bound up nutrients in the soil and no additional base fertiliser would be needed. Within about a month of planting it was significantly poorer than the area which had conventional fertiliser, which soil tests had shown was required.

If coming out of permanent pasture, the amount of nitrogen required is likely to be minimal if at all – particularly if there has been a lot of effluent applied – but on continuously cropped ground, nitrogen in both the starter fertiliser and side-dressing will be required.

Di Ammonium Phosphate at 250kg/ha is a good starter fertiliser where phosphorus levels are low or only just adequate. And there are currently a couple of importers selling DAP considerably cheaper than the two main co-ops, but this needs to be pre-ordered to ensure supply.

Side-dressing

If phosphorus levels are high, then using a product like Calcium Ammonium Nitrate at 150kg/ha is a cheaper option as a starter fertiliser.

Using SustaiN nitrogen as a side-dressing may be slightly more expensive than straight urea, but as this is applied coming into summer, having the protective Agrotain coating which reduces volatilisation for these higher rates of N needed does give greater insurance that the N will be taken up by the crop.

On low sulphur soils Sulphate of Ammonia can be considered for side-dressing. The N lost through volatilisation from SOA is very minimal and only a fraction of what is lost even when using SustaiN. However, if using sulphur in the base fertilisers, the sulphur demands of the maize may have already been met and SOA is a more expensive source of N than urea or SustaiN.

ROBIN BOOM CPAg, member of the Institute of Professional Soil Scientists