Aluminum (Al) toxicity is a major yield‐limiting factor in winter wheat production in many parts of the world. The use of Al‐tolerant cultivars reduces the impact of this problem and is common to the southern Great Plains where wheat is managed as a dual‐purpose crop. However, no quantitative data exist on the Al tolerance ranking of winter wheat cultivars often grown in a dual‐purpose management system. This study was established to classify on a field scale the Al tolerance of common winter wheat cultivars (Ok101, Ok102, 2137, 2174, Jagger, Jagalene, Custer, and AP502CL). Fall forage yield of each cultivar was harvested by hand clipping. Soil samples were collected at the same time and analyzed for pH and Al saturation (Alsat). Grain was hand‐harvested in June of each year from the same rows harvested for forage. Cultivar differences (P < 0.1) were found in forage and grain yields for the Alsat > 30% range. Al tolerance based on grain yield ranked as follows: 2137 > Jagalene = Ok101 > Jagger = 2174 ≥ Ok102 > Custer = AP502CL. Al tolerance based on forage yield ranking was similar to that of grain: 2137 > Ok101 = Jagalene = Jagger > 2174 = Ok102 > Custer = AP502CL. Grain yield seemed to be less affected by Alsat than forage yields. The use of Al‐tolerant winter wheat cultivars may minimize producers' risk of crop loss; therefore, this ranking of Al tolerance should help winter wheat producers make informed decisions if they have acid soils with high Al content and no other remedies available.

The components that define cereal-grain yield potential have not been well defined. The objective of this study was to collect many differing biological measurements from a long-term winter wheat (Triticum aestivum L.) study in an attempt to better define yield potential. Four treatments were sampled that annually received 0, 45, 90, and 135 kg N ha −1 at fixed rates of phosphorus (P) (30 kg ha −1 ) and potassium (K) (37 kg ha −1 ). Mid-season measurements of leaf color, chlorophyll, normalized difference vegetative index (NDVI), plant height, canopy temperature, tiller density, plant density, soil moisture, soil NH 4 -N, NO 3 -N, organic carbon (C), total nitrogen (N), pH, and N mineralization potential were collected. In addition, soil texture and bulk density were determined to characterize each plot. Correlations and multiple linear-regression analyses were used to determine those variables that can predict final winter wheat grain yield. Both the correlation and regression analyses suggested mid-season NDVI, chlorophyll content, plant height, and total N uptake to be good predictors of final winter wheat grain yield. Keywords

The Mehlich 3 (M3) method is widely used for extraction of plant-available phosphorus (P) from soil over a wide range of pH values. The method is also used by many laboratories to determine multiple plant-available nutrients simultaneously. However, this method has not been statistically validated within and among laboratories. The objective of this study was to determine the repeatability (within-laboratory performance) and reproducibility (among-laboratories performance) of the M3 method by using a wide variety of soils. An in-house homogeneity test was conducted for 10 soils. Three replicates of each of the 10 soils were sent to 26 domestic and international laboratories primarily for P analysis. Samples were scooped, weighed, or both scooped and weighed for extraction. The P in extracts was quantified by the participating laboratories by using inductively coupled plasma-atomic emission spectrometry (ICP-AES) or colorimetrically. For the scooped samples analyzed colorimetrically, the repeatability relative standard deviation (RSDr) ranged from 2.07 to 12.1; the RSDr ranged from 2.2 to 21.4 for the scooped samples analyzed by ICP-AES. For the weighed samples analyzed colormetrically, the RSDr values were 1.099.34, and for the weighed samples analyzed by ICP-AES, they were 1.705.76. For the reproducibility data, the RSDR values ranged from 6.85 to 50.8 for the scooped-colorimetry category, from 6.95 to 73.9 for the scooped-ICP-AES category, from 7.19 to 42.6 for the weighed-colorimetry category, and from 5.29 to 35.9 for the weighed-ICP-AES category. The greatest RSD values were associated with the Susitna soil, which had the smallest concentration of extractable P. Because of the relatively small concentration of P in this soil, the laboratories were attempting to measure solution concentrations that were close to the detection limits. The Horwitz ratios (HorRat) were also used to evaluate the repeatability, HorRat(r), and reproducibility, HorRat(R). Overall, the M3 P method appears to be both repeatable and reproducible across the 4 categories, and the vast majority of the HorRat values for both repeatability and reproducibility were within the acceptable range. The results of this study indicate that the M3 P method for the determination of plant-available P in soil is both accurate and precise when standardized procedures are used. The method has been shown to be suitable for use as a reference method for testing soil materials for extractable P.

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