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A total soil organic P (TPo) method that retains the relative ease of the dry combustion method and still preserves essentially all organic P in the extract would be desirable. A sequential extraction procedure for TPo with concentrated sulfuric acid and dilute base was therefore developed to meet these objectives. The method was based on the high efficiency of Po extracted from soils by the heat of solution created by addition of water to concentrated H2SO4. In this step of the procedure, 79% of the total Po was extracted. The acidic soil residue was next treated with NaOH to complete the extraction of Po. The sum of the acid‐ and base‐extractable Po gave a measure of the total soil Po. The method did not hydrolyze or only minimally hydrolyzed Po substrates added to test soils. The proposed procedure was compared with the Mehta extraction method, and with an ignition method developed by Saunders and Williams. In a test of 12 different soils (prairie to highly weathered) the proposed procedure extracted an average of 4% more Po than did the Mehta, and 17% less Po than the Saunders and Williams procedures. The proposed procedure is more rapid than either of the other procedures, and is equally precise. The ease with which the proposed method can be performed as stated, or performed in combination with the high temperature base extraction of the Mehta procedure, makes it ideal for routine laboratory use, especially when the nature of the Po compounds also is being investigated.

Soil organic P is an important source of plant‐available P in the Great Plains. It is, therefore, important in conservation tillage agriculture, that we know the size and the potential availability for crop use of this large P pool, which could exceed one‐half of the total P. We propose a one‐step procedure with hot basic EDTA (ethylene diaminetetraacetic acid) for total soil organic P that requires minimum manipulation and analytical prowess. Soil samples (0.5 g) were incubated for 2 h at 85 °C with 25 mL of 0.25 M NaOH + 0.05 M Na2EDTA, after which time the organic P in the extracts was determined by persulfate oxidation. Results from the evaluation of nine soils from various parts of the USA and one Canadian soil showed significant correlations with an existing wet sequential extraction and a dry high‐temperature ignition method for total organic P determinations. With the high‐organic‐matter Canadian soil, the EDTA method extracted 32% more organic P than the wet extraction method, and essentially the same as the dry ignition method. The new method appears to be especially useful for soils where organic acids and chelation mechanisms with P may be more dominant than ester‐type formations.

Winter wheat (Triticum aestivum L.) is the most common dryland crop grown in the central Great Plains. Producers in this region include fallow in the rotation to minimize yield variability due to erratic precipitation. However, fallow degrades soil quality by increasing erosion potential and loss of organic matter. Fortunately, minimum‐till production systems and residue management improve water use efficiency by plants, thus producers can crop more frequently. We evaluated eight rotations comprised of various sequences of winter wheat (W), corn (Zea mays L.) (C), proso millet (Panicum miliaceum L.) (M), sunflower (Hettanthus annum L.) (S), and fallow (F) in comparison to W‐F at Akron CO. Our goal was to identify rotations that can replace W‐F to minimize the frequency of fallow. The soil was a Weld silt loam (Aridic Paleustoll). Continuously cropping with W‐C‐M and W‐M almost doubled total grain yield compared with the conventional system of W‐ F. Other rotations such as W‐C‐F, W‐C‐S‐F, and W‐C‐M‐F yielded >60% more on an annualized basis than W‐F. Winter wheat yield increased with longer time intervals between wheat crops. Sunflower yielded the most when grown only once every 4 yr; more frequent cropping favored diseases. Sunflower reduced yield of the following crop, especially during dry years. Yield variability was highest with corn and sunflower, whereas proso millet showed the least variability. Producers can manage yield variability by diversifying crops in the rotation, as annualized yield variability of W‐M and W‐C‐M was similar to W‐F. With residue maintenance and minimum tillage, producers can crop more frequently, thus increasing land productivity while minimizing the frequency of fallow in this semiarid region. Research Question Since the 1930s, winter wheat‐fallow has been the prevalent crop rotation for the semiarid Central Great Plains. Because available water is usually the most limiting resource, producers rely on fallow to minimize the impact of erratic precipitation on grain production. However, fallow degrades soil quality by increasing erosion and loss of organic matter. Development of minimum‐till production systems has altered the water relations in our agroecosystems. Minimizing tillage leaves more crop residue on the soil surface, subsequently increasing precipitation storage and water use efficiency of crops. Thus, with minimum‐till systems, more intensive cropping is possible in the central Great Plains. This study evaluated cropping systems composed of various sequences of winter wheat (W), corn (G), proso millet (M), sunflower (S), and fallow (F), including continuous cropping. Our goal was to identify rotations that may be successful alternatives to W‐F. Literature Summary With reduced‐till systems, several crops have been successful in a wheat‐summer crop‐fallow rotation in this region, including proso millet, corn, and grain sorghum. In addition, longer rotations with three crops in 4 yr, such as W‐C‐M‐ F, are also successful and have increased land productivity by 70%. Another p...

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Continuous cropping or decreasing the frequency of summer fallow (F) in cereal‐based dryland rotations may have benefits other than greater water utilization and erosion control. We hypothesized that rotations with no fallow or minimum fallow frequency can produce more biomass and cover than the traditional winter wheat (Triticum aestivum L.)‐summer fallow systems (W‐F), and ultimately, greater amounts of soil organic matter (SOM). To this end, we evaluated changes in various pools of SOM at the 0‐ to 5‐ and 0‐ to 15‐cm depths on a Weld loam (fine, smectitic, mesic aridic Paleustolls) that were caused by (i) decreasing fallow or increasing cropping intensities, (ii) specific rotations of the same length but with different crop sequencing, and (iii) accumulated residue and roots from reduced‐ or notillage from 1993 to 1997. Total soil organic carbon (SOC) and N for the 0‐ to 5‐cm depth increased by =20% with continuous cropping rotations compared with W‐F rotations. Particulate organic matter‐carbon (POM‐C) doubled, while POM‐N, and soluble organic C (OC) increased by one third for the same comparison. At the 0‐ to 15‐cm depth, SOC, POM‐C, and POM‐N did not differ among systems with fallow, nor among systems with cropping intensities greater than W‐F. Thus, significant differences always existed between W‐F and continuous cropping. Generally, fallow had a negative influence on SOC accumulation, and continuous cropping a positive influence on surface SOM. Changes in SOC did not correlate with yields in the five‐year comparison of this ongoing study.

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