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Published: 2008-08-29 00:00:00

By EW sustainable agriculture coordinator Gabriele Kaufler
Farmers can potentially save themselves big money if they plan well ahead for the maize growing season starting at the end of September.

Maize requires significant amounts of nutrients to produce a decent crop. Recent trials in the Waikato have shown that a maize silage crop of 24-27toDM/ha removes about 290kgN, 40kgP and 320kgK per ha.

But, on dairy farms especially, you might find that there are already significant levels of nutrients in the soil and not a lot of extra fertiliser might be needed to meet crop requirements. So it is important to soil test the paddocks earmarked for planting maize this spring.

Maize sends its roots deep down into the soil (up to 1.5 metres) meaning it can uptake nutrients which might have washed deeper into the soil, especially potash and nitrogen.

Standard sampling to 15cm depth does not give you any information on the subsoil’s fertility, meaning deep soil sampling is advisable. Sampling in two increments of 0-15cm and 15–30cm is best for a sound understanding of your soil’s nutrient resources.

When cultivating a paddock, nitrogen will be released as nitrate from the soil organic matter. Nitrate is plant available but can quickly wash through the soil and leach out to the groundwater. Therefore it is important to capture what is there before it moves deeper into the soil.

I recommend sampling for available nitrogen in the soil well after cultivation. Soil sampling 4-6 weeks after planting will enable you to adjust the amount of nitrogen that needs to go on as side dressing. Most likely you will find a lot of plant available nitrate and, if so, you can confidently reduce or even skip urea dressings altogether.

Sampling for available nitrate in two increments of 0-30cm and 30-60cm gives you a much better picture of what is accessible to the roots down there. This is standard practice in Europe and works well.

For paddocks that have been cropped long term it is a good idea to sample for organic matter to monitor trends. Check with your contractor for cultivation options available. Minimum tillage is better for your soil and will reduce the loss of organic matter.

Applying dairy effluent to feed your crop will help to get some organic matter back into the soil. Think about approaching your dairy farming neighbour. There might be an opportunity to obtain effluent or feedpad scrapings. Please remember that a maximum load of 200kg N/ha from effluent applied to maize crops is allowed in the Waikato region.

But before you spread it you need to know the nutrient content of the effluent going on. So it is essential to sample the effluent beforehand and work out the application rates from there.

Many dairy farmers who grow maize on-farm prefer to plant the crop at the back of the farm so that cows don’t have so far to walk to the shed. But many paddocks closer to the shed receive nutrients from effluent irrigation. These paddocks quite often have high potash and nitrogen levels, making them ideal to grow maize on. Most likely you won’t have to add fertiliser there, and that’s an instant saving of$500-plus a hectare.

Trials last year on Waikato farms also revealed that, if applying standard urea dressings, you might end up with a lot of nitrogen left behind in the soil after harvesting. In the trials we found between 117 and 300 kgN/ha still sitting there unused. That is money down the drain as most of this nitrogen will have washed out of the rootzone with the winter rainfall we’ve recently experienced and it is posing a huge risk to the environment.

When working with a consultant or fertiliser rep to plan for this season’s maize crop, please make sure they are aware of these results and ask them to take a deep soil sample for available nitrogen in the two increments of 0-30cm and 30-60cm.

It is also important to standard soil test your future maize paddocks to at least 15cm depth while they are still in grass. Checking out the lower topsoil nutrients by sampling 15–30cm is strongly recommended to be able to make sound nutrient management decisions for your crop.

Around 30 per cent of North Island dairy farms have twice the level of soil nutrients needed for pasture or crop growth. This means that up to one-third of dairy farmers are probably spending more on fertiliser than they need to. Especially high input farms are likely to be in that category. Check your nutrient budgets and previous soil test results now to plan for the new season.

Fertiliser is one of the largest expenses for most farm businesses. It is important to recognise that farmers enacting a nutrient management plan for their cropping activities have reported significant fertiliser savings. This is a win-win, improving the economic and the environmental performance of the business – both are good reasons to have a closer look at your nutrient management options.

Please keep in mind, that under Environment Waikato's Regional Plan every farmer applying more than 60 kilograms of nitrogen per hectare a year to their land now requires a nutrient management plan.

Whenever cultivating, make sure to leave a buffer zone of uncultivated land alongside all sensitive areas. This is your waterways and drains, but also wetlands, seeps and areas with native vegetation.

Do not push soil into these areas either and ask yourself how much valuable cropping area you realistically would win if you did. Quite often these areas fail to grow a decent crop anyway and are a hassle all the way through. Under Environment Waikato’s Regional Plan a two-meter bufferstrip is required for all cultivation activities.

Cultivation of steeper paddocks creates a huge erosion risk and we have seen a lot of valuable topsoil being washed off these areas this year. Is it worth spending money to cultivate these parts of your farm? Quite often they fail to grow a good crop and the pasture renewal program fails too, as pasture relies strongly on the topsoil quality. If topsoil is lost the pasture will struggle for years to come.

For more advice, call Gabriele Kaufler, sustainable agriculture coordinator, Environment Waikato on 0800 800 401.