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1 September 2018 Jessica Dunbar

Spring crop paddock selection

Soil testing is an important tool in your cropping calendar. It can be utilised to assist in selecting the correct paddocks to use for high value crops, like fodder beet, and for selecting which paddocks can be planted with a lower value crop in order to start the process of increasing soil fertility in areas lined up for pasture renewal.

Soil testing provides the ability to develop a tailored fertiliser programme and focus on the key nutrients required for your farms maintenance programme, or for a specific crop. Fertiliser spend makes up a significant portion of the farm budget, therefore it is always worth taking a measured approach and only applying the nutrients that are needed.

So what are nutrients? They are the 16 mineral elements that plants and animals require to grow and function, with plants getting their nutrients from the soil. Soil testing prior to planning for the season ahead gives a base foundation and understanding for the nutrient levels you are working with. In your farming system, growth or yield will be limited by the nutrient in shortest supply.

Soil testing is an essential component when it comes to nutrient interactions. Having an abundance of one nutrient can effectively antagonise another, or vice versa, where you have a synergy of increased availability of one nutrient due to the increase in level of another nutrient. For example, excess potassium leads to an imbalance of magnesium and calcium, which can have an effect of poor yield or quality, as well as the potential for metabolic disorders in stock to arise.

Another reason behind soil testing is for developing trends across your farm system against previously collected data. It is recommended that you get your PGG Wrightson Technical Field Representative, or Ballance Agri-Nutrients representative to soil test at the same time every year, to maintain consistency. Taking samples six to eight weeks out allows for tests to be sent away, analysed and sent back to develop effective fertiliser programmes.

Sampling depth for soil testing is directly related to the potential rooting depth of the crop. Pasture, or herb paddock samples should be taken at 75 mm, and arable or cropping paddocks sampled at 150 mm in depth.

Fertiliser inputs will be based on your soil test results and will determine if your fertiliser programme is maintenance, or capital. Maintenance nutrient requirements are the quantity of fertiliser nutrients required to maintain a particular soil test level over a one year period. Capital nutrient requirements are the quantity of fertiliser nutrients required to increase the soil test value to the optimum target value, for example increasing soil fertility levels to get an optimal Olsen P for the soil type and farm production level.

Taking a soil test to determine soil nutrient levels, prior to planting crops and applying maintenance fertiliser over the whole farm ensures rates of nutrients applied are in line with dry matter yield goals for your crops and overall farm production goals. Knowing what nutrients are already present in your soil also helps to avoid applying excess fertiliser, thus helping to farm in an environmentally sustainable manner.

For more information on soil testing, contact your local PGG Wrightson Technical Field Representative.

Jessica Dunbar

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