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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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.

Variable influence of the environment on early‐season plant growth leads to similarly variable yield levels from year to year. This study was conducted to determine the ideal point in the growing season when normalized difference vegetation index (NDVI) sensor readings were highly correlated with grain yield. For each site‐year, NDVI readings were collected at least seven times from December through April. Readings were collected from two long‐term experiments where an N response was expected in plots that historically received different N rates. The number of days from planting to sensing where growing degree days (GDD) were more than 0 (GDD > 0) was tabulated by site‐year for all dates when NDVI data were collected. The r2 was computed for NDVI versus final grain yield at all sensing dates and plotted against the respective GDD > 0 when readings were taken. Linear plateau models were used to determine the point when the r2 peaked. Averaged over 3 yr (2016–2018), the optimum GDD > 0 needed to predict grain yield using NDVI in both long‐term trials was between 97 and 112. Use of the GDD > 0 as a numeric metric to delineate the best time and date to collect NDVI readings and predict yield potential can then be used to formulate accurate midseason fertilizer N rates. Adhering to quantitative GDD > 0 data is much more reliable than using subjective morphological scales. These critical GDD values can be reported on a day‐to‐day, by‐location basis (http://mesonet.org) for in‐season producer use.

Average maize grain yields in developing countries are 1.8 Mg ha -1 compared to 9.9 Mg ha -1 in the USA, with much of this due to planter technology. Thirty million hectares in the world are planted by hand, where 2 to 3 seeds are placed per hill at uneven spacing resulting in heterogeneous plant stands. A hand planter was built to deliver single seeds with each strike (singulation) and to improve low grain yields encountered in developing countries. This study was conducted to evaluate drum cavity size and planter tip on singulation and plant emergence in maize, using the OSU hand planter. Two drum cavity sizes, two planter tips and four different seed sizes were used in a two-year study, started in 2014. On all four site years drum cavity 450S resulted in significantly similar emergence as those checks planted by hand and a John Deere vacuum planter. Over site years 17% better emergence was achieved with 450S vs 260-20 drums. Drum 260-20 was better at delivering singulation than 450S however, over four site years 27% misses (no seed delivered) were recorded with drum 260-20. No significant difference was seen with different tips on emergence, singulation and final grain yield. This data suggests that maize producers in developing world could use the OSU hand planter with drum 450S and the conventional tip. This planter can be used as a side-dress N-fertilizer applicator by simply changing the internal drum, that incorporates urea into the soil, minimizing volatilization losses. It also removes chemically treated seed from producer hands thus reducing health risks.iv