How do you assess how well last season’s crop nutrition management shaped up? Every grower knows how much they spend on crop nutrition. They do not always know if it was well spent. A good crop nutrition program maintains soil fertility, and supplies what is needed to meet the productivity expected – while balancing risks and returns. Keeping good records of crop yield, rotations and fertiliser history are central to calculations and useful review of performance.
Webinar: Review crop nutrition in your paddocks
Recording coming soon
As part of the More Profit from Crop Nutrition national extension program, Chris Dowling presented a webinar for advisors and growers from all Australian grains regions on the techniques described below.
Partial Factor Productivity
Partial Factor Productivity (PFP) is a broad measure of the efficiency of grain production in relation to the rate of a specific nutrient applied. High values suggest the crop may still be responsive to higher nutrient rates. Low values suggest grain yield response from further nutrient application is declining. Analysis of the PFP of several nutrients can reveal nutrient interactions associated with yield response.
The effectiveness of nitrogen management can be assessed through the grain protein percentage. The optimum protein percentage in wheat grain varies among cultivars but is often 11 to 12%. If crops achieve protein levels below these optimum levels further nitrogen application may have increased yield. Crops achieving above optimum protein levels, but with good grain size, may reflect an uneconomic overuse of fertiliser or fertiliser applied too late in the season. In-season N generally needs to be applied before booting to give a yield response.
Grain protein percentage is required to calculate the Partial Nutrient Benefit (PNB) of Nitrogen, which is accepted internationally as the measure of Nitrogen Use Efficiency at national levels, and is easily downscaled to paddocks, farms or regions.
Nutrient test strips
Test strips are an investment in improved nutrition for later seasons. The effect of the different practices in the test strip may be seen in the grain yield at harvest. On farm test strips with higher nutrient rates can tell you whether applying more or none of a particular nutrient would have delivered a yield response.
- Nutrient rich test strips help evaluate the fertiliser regime used, especially where there is uncertainty about the best rate to apply. Nitrogen (N) rich strips are the most common type of on farm test.
- Nil test strips can be used to check the effect of dropping a nutrient from a crop nutrition regime. Yield from a nil strip is needed to calculate the Agronomic Efficiency of the nutrient application to the rest of the paddock. Agronomic Efficiency is one of the best measures of the economic value of nutrient applications.
Grain tissue testing
Tissue testing of grain is valuable for assessing trace element availability in a paddock – notably copper (Cu), zinc (Zn), and maybe manganese (Mn). If levels in the grain are lower than they should be, there is a need to distinguish between deficiency – when the nutrient is not there in sufficient quantity – and inefficiency – when the nutrient is there but there are problems in availability and uptake.
The quantity of nutrients that are exported in grain can be used to develop a crop nutrient replacement strategy. Keeping a record of nutrient export over successive crops will fine-tune understanding of the paddock’s nutrient status.
Soil testing can be used to track the fertility of a paddock, as well as to inform fertiliser recommendations for next season based on critical ranges. Long term declines in nutrient levels, soil organic matter or pH suggest that soil condition is declining under the farm system. Some nutrient problems can be addressed within a crop nutrition regime. Other issues may need a bigger system review to change the trend.
Rob Norton, IPNI, Chris Dowling, Back Paddock Co.