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A current estimate of global phosphorus use effi ciency (PUE) for cereal production is not available. Th e objectives of this paper were to estimate PUE for cereal crops grown in the world and to review methods for improvement. Phosphorus use effi ciency was determined using world cereal harvested area, total grain production, and P fertilizer consumption from 1961 to 2013, in addition to assumptions established from previous literature. World PUE of cereal crops was calculated using both balance and diff erence methods. Using the balance method, cereal grain P uptake is divided by the P fertilizer applied. Alternatively, the diff erence method accounts for P coming from the soil and that is subtracted from applied P. Utilized in this analysis is the estimate that cereal production accounts for 61% of the total harvested cropland. Cereal grain yields increased from 1.35 to 3.90 Mg h -1 between 1961 and 2013. In 1961, the world's fertilizer P consumption was 4,770,182 Mg and increased to 16,662,470 Mg of P fertilizer by 2013. Th is represents a 3.5× increase in P fertilizer consumption over 53 yr. Phosphorus use effi ciency estimated using the balance method was 77%. Using the diff erence method, PUE for cereal production in the world was estimated to be 16%.

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Core Ideas Potassium use efficiency in cereals is unknown. World demand for potassium in agriculture is increasing. Potassium is a non‐renewable resource. Worldwide potassium (K) fertilizer use has grown, while the expected fertilizer use efficiency has decreased. The objective of this paper was to estimate potassium use efficiency (KUE) for cereal crops and report on methods that will most likely lead to improved KUE. World KUE was calculated using the total area under cereal production, total cereal grain production, percent K content in cereal grains and K fertilizer consumed from 1961 to 2015. All data was obtained from FAOSTAT except percent K grain content, which was acquired from the USDA. The reported KUE estimate included assumptions established in prior literature. The percent K coming from the soil was estimated at 71%, while previous year K fertilizer‐residual‐effects were offset by knowing that similar amounts of fertilizer K will be applied in following years. At current consumption rates, existing K reserves as K20 are estimated to last 100 yr meaning that mining operations will need to expand to meet expected market demands. Results showed that cereal production increased by a factor of 3.2 from 1961 to 2015 and that was accompanied by a threefold increase in fertilizer K consumed. Estimated KUE from 1961 to 2015 for world cereal crops using the difference method was 19%. Combined with findings from this paper, estimates of N, P, and K use efficiency for cereal production in the world stand at 33, 16, and 19%, respectively.

Sulfur (S) is an essential plant nutrient needed for higher crop yields and improved nutritional value. In recent decades, the occurrence of S deficiency has increased and fertilizer S use may steadily increase. This may lead to inefficient crop utilization of S and result into negative footprints on the environment. The objective of this work was to estimate world fertilizer sulfur use efficiency (SUE) for major cereal crops grown around the world. A 10‐yr data set (2005–2014) was obtained from the Food and Agriculture Organization, the US Geological Survey, and an array of other published research articles. Statistical analysis was performed using MS Excel to obtain total area for world and cereal crops, grain yield, and fertilizer S applied. The difference method [(Total grain S – grain S derived from the soil)/S applied] was used to compute world SUE. Cereal crops included in this study were barley (Hordeum vulgare L.), maize (Zea mays L.), rice (Oryza sativa L.), millet (Pennisetum glaucum L.), wheat (Triticum aestivum L.), sorghum (Sorghum bicolor L.), rye (Secale cereale L.), and oat (Avena sativa L.). Cereal production increased from 2669 M Mg in 2005 to 3346 M Mg in 2014. Sulfur use efficiency for cereal crops was estimated to be 18%. This low SUE may be attributable to S leaching from the soil profile, immobilization, retention in residues, and adsorption. As increased quantities of fertilizer S are likely to be applied in future to meet the ever‐growing demand for food, SUE could decline below 18%. Core Ideas World sulfur use efficiency for cereal crops is unknown. World sulfur use efficiency for cereal crops was estimated to be 18%. More precision agriculture research is necessary to improve sulfur use efficiency for cereal crops. Reasons for low sulfur use efficiency include sulfur; leaching, adsorption, retention in residues, and immobilization as well as failure to adhere to sound agronomic practices and 4R concepts.

Predicting required fertilizer N rates before planting a crop embodies the concept of establishing a pre-season yield goal and fertilizing for that expected yield. The study evaluates prediction of yield goals using data from long-term experiments. Winter wheat (Triticum aestivum L.) grain yield data from the Magruder plots (Stillwater, OK, 1930-present), Exp. 222 (Stillwater, OK, 1969-present), and Exp. 502 (Lahoma, OK, 1970-present) were used. Annual pre-plant N rates were applied for 87, 45, and 44 yr, respectively. Experiments 222 and 502 used randomized complete block experimental designs. This manuscript applied the theory that average yields over the last 3 to 5 yr can be used to predict the ensuing years' yield, or yield goal. For the Magruder plots, the "NPK" (67-15-29, N-P-K) and Check (0-0-0) Treatments were used. For Exp. 222, Treatments 1 and 4 (0-30-37 and 135-30-37) and in Exp. 502, Treatments 2 and 7 (0-20-55 and 112-20-55) were selected to test this concept. Wheat grain yield averages for the prior 3, 4, and/or 5 yr were not correlated with ensuing season yields in all three long-term experiments. Over sites and years, yield goal estimates were off by up to 3.69 Mg ha -1 . Failure of the yield goal concept to predict current-year yields is due to the unpredictable influence of environment. Mid-season prediction of yield potential using active sensors is a viable alternative for improved in-season cereal fertilizer N recommendations.

The second law of thermodynamics states that entropy or randomness in a given system will increase with time. This is shown in science, where more and more biological processes have been found to be independent. Contemporary work has delineated the independence of yield potential (YP0) and nitrogen (N) response in cereal crop production. Each year, residual N in the soil following crop harvest is different. Yield levels change radically from year to year, a product of an ever‐changing and unpredictable/random environment. The contribution of residual soil N for next years’ growing crop randomly influences N response or the response index (RI). Consistent with the second law of thermodynamics, where it is understood that entropy increases with time and is irreversible, biological systems are expected to become increasingly random with time. Consequently, a range of different biological parameters will influence YP0 and RI in an unrelated manner. The unpredictable nature that environment has on N demand, and the unpredictable nature that environment has on final grain yield, dictate the need for independent estimation of multiple random variables that will be used in mid‐season biological algorithms of the future. Core Ideas Randomness in biological systems is increasing. Many biological processes are independent. Yield levels change from one year to the next. Environments change over time and are random. Optimum fertilizer nitrogen rates change dramatically from year to year.

Method of N application in winter wheat (Triticum aestivum L.) and its impact on estimated plant N loss has not been extensively evaluated. The effects of the pre‐plant N application method, topdress N application method, and their interactions on grain yield, grain protein concentration (GPC), nitrogen fertilizer recovery use efficiency (NFUE), and gaseous N loss was investigated. The trials were set up in an incomplete factorial within a randomized complete block design and replicated three times for 5 site‐years. Data collection included normalized difference vegetation index (NDVI), grain yield, and forage and grain N concentration. The NDVI before and after 90 growing degree days (GDD) were correlated with final grain yield, grain N uptake, GPC, and NFUE. At Efaw location, NDVI after 90 GDDs accounted for 58% of variation in grain yield and 51% variation in grain N uptake. However, NDVI was found to be a poor indicator of both GPC and NFUE. Grain yield was not affected by the method and timing of N application at Efaw. Alternatively, at Perkins, topdress applications resulted in higher yields. The GPC and NFUE were improved with the topdress applications. Generally, topdress application enhanced GPC and NFUE without decreasing the final grain yield. The difference method used in calculating gaseous N loss did not always reveal similar results, and estimated plant N loss was variable by site‐year, and depended on daily fluctuations in the environment.