Miller Magazine Issue:114 June 2019

82 ARTICLE JUNE 2019 plant will direct the Nitrogen towards producing protein. If there is enough water available throughout the growth and development stages then the Yield and the Protein will be determi- ned by the availability and uptake of nutrients of which Nitrogen is the most important. Protein/Nitrogen/Yield Balance: Protein is related to Nitrogen as discussed above, however the relationship between Protein and Yield is not so obvious. In 2013, Greg McDonald and Peter Hooper, University of Adelaide, School of Agriculture, wrote an article for the GRDC titled: Nitrogen De- cisions – Guidelines and rules of thumb. They referenced a paper written in 1963 by JS Russell for the Australian Journal of Experi- mental Agriculture and Animal Husbandry where he “described the idea of using grain protein concentration to assess the like- lihood of N responsiveness in wheat cropping systems. He sug- gested that yield responses were most likely when grain protein concentration was < 11.4%”. McDonald and Hooper went on to say, “Based on recent trial data, the general conclusion still appears valid: 100% of all trials where grain protein concentration of the unfertilised control was <8.5% were responsive to N and would have given yield response of 14kg/kg N. When grain protein con- centration was >11.5%, only 32% of the trials were responsive to N and the mean yield response was zero”. They concluded; “While this relationship can’t be used to make in-season N deci- sions it may be useful in helping to assess the degree of N stress during the previous season and making post-harvest assessments of N management strategies, which can help in future plannings.” Other scientists and agronomists have written about the relati- onship between Protein content of the finished grain and the Yield. Steve Larocque, Beyond Agronomy, Alberta, Canada, publishes a newsletter that is read by more than 8000 precision farmers and agronomists around the world. Mr Larocque pointed out in his newsletter that there is a fine balance in applying Nitrogen to a barley crop where the objective is to optimize the yield and restrict the protein to less than 13%. He states, “The hard part is finding the right nitrogen rate to produce maximum yield with a prote- in that falls below 13% but higher than 12%. When your malt protein is lower than 12.5% you know you’re leaving yield on the table. If you shoot too high you end up with high protein and no malt selection.” Mr Larocque referred to the balance as the “Sweet Spot” where the yield was optimized and the protein gra- de realised the highest crop payments. Thane Pringle, Independent Precision Agriculture, Yenda, NSW, explains how Nitrogen is used by plants and how Nit- rogen is made available from the soil to the plants. He showed a plot (Figure 3.) of Yield vs. Nitrogen Fertilizer Application vs. Protein content of the grain. Brill et al state in their original paper, “As the rate of N supply is increased, yield will generally increase to a maximum level, whereas protein may continue to increase with further N application. This is demonstrated by the results from a trial at Parkes in 2011, sown as part of the GRDC- funded Variety Specific Agronomy Project (Figure 3). Wheat yield was responsive to N fertiliser but at a reducing rate where N was applied in 30 kg/ha increments. Yield was maximised with N application of 90 kg/ha. Protein increased linearly for each 30 kg/ha increment up to 120 kg/ha N. In this trial, yield appeared to be maximised at a grain protein concentration of 11.2 %, a useful ‘rule of thumb’ in deciding whether a crop was yield limited by N.” Professor Roger Sylvester-Bradley, UK, in a HGCW booklet tit- led Nitrogen for Winter Wheats—Management Guidelines, wrote, “Grain protein with optimum N for yield in feed varieties is con- sistently about 11% (1.9%N). Bread making varieties optimise for yield at around 12% protein and often need extra N to achieve a market specification of over 13%. Low grain protein – less than 10% for feed varieties – Indicates sub-optimal N use.” Figure 6. Protein and Yield Maps, 2016. Figure 7. Protein/Yield Correlation Maps