Whether you have recently acquired land or have had it a long time, changes in seasonal conditions, crop input expenses and commodity prices means your soil nutrition strategy will always need adaption.
Given last year’s exceptional rainfall, farmers could be forgiven for being left scratching their heads about the nutrient levels in their soils: How much did my 2016 crop remove? Did the nutrients leach to a deeper level and can the 2017 crop access them? How much will the heavy stubbles lock up? How much will burning stubbles remove?
It’s important to have a soil monitoring program with soil testing to determine your nutrient starting point to prevent in-season deficiencies. Â
Early 2017 soil test results conducted by BCG for growers across the Wimmera and Mallee are showing, on average, moderate to low phosphorous (P) levels following cereals and canola, and nitrogen (N) levels to 70cm are ranging from 40kg N/ha following wheat to over 100kg N/ha following fallow.
Soil samples should be sent to a reputable laboratory and growers should also be careful with the interpretation of their results and seek advice from a good agronomist if they are unsure. The critical values offered in some reports are often a guide only and may not be relevant to your soil type or to the depth of the soil sample.
In general, soil sampling depth of 0-10 cm is adequate for P but conduct soil tests to depth for a more accurate indication of the N, sulphur (S) and potassium (K) status of your soils. Ideally sampling depth should capture the root zone and this will vary according to the crop type and soil type.
Deep N soil testing (for example 0-10, 10-60 cm) is a well-established practice. Including K and S when conducting deep soil tests will provide better value for your testing dollar.
If you are testing for P, make sure you get Colwell P and PBI and also DGT if the option is offered.
Soil tests can often suggest more nutrients should be applied however a response to fertiliser application is not always observed. Â
Recent GRDC-funded research through the More Profit from Crop Nutrition (MPCN) initative suggests critical soil test levels can be the first point of inaccuracy and interpretation needs to be refined for different soil types associated with your paddock. (An accurate soil test for available soil sulphur and potassium, project UA00140).
One way to validate your soil tests and to assess the most cost effective rate of fertiliser for your crop is to use paddock strip trials, and sowing is a good time to plan your on-farm trial.
The key is to keep it basic by testing one variable, such as fertiliser rate or seeding rate, and set up the trial with a number of treatments.
Ideally, trials should contain a control (0 rate), standard rate (replacement if testing a nutrient) and a rich strip (2-3 x replacement if testing a nutrient) and always validate with harvest yield results. Try to ensure other potential variables, such as N or weed pressure, is non-limiting so any crop response can be associated the question you are investigating.
Where possible, it is best to replicate your test strips so you can rule out any influencing factors.
This article was published in the Stock and Land on April 20.Â
