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Osmar Alves Carrijo and George Hochmuth

Experiments were conducted to evaluate the yield response of tomato (Lycopersicon esculentum Mill.) to P, either preplant-incorporated or injected through the drip irrigation system, on soils with low, high, or very high soil P content. Fertilization through the drip irrigation system (fertigation) was more efficient than preplant incorporation of P for soil that tested low in P (9 mg·kg–1 Mehlich-1 P). On soil testing low in P, marketable yield response to preplant soil P application rates (0 to 100 kg·ha–1) was maximum at 61 kg·ha–1 P according to the linear-plateau model, but 37 kg·ha–1 P according to the quadratic-plateau model. The lower value is about one-half the P recommended by Univ. of Florida for low-P soils. On soil testing high in P (48 mg·kg–1 Mehlich-1 P) the linear-plateau model predicted a maximum yield of 72.8 t·ha–1 with 25 kg·ha–1 P. The Univ. of Florida recommended no P for that soil. On soil testing very high in P (85 mg·kg–1 Mehlich-1 P), there was no yield improvement with P fertilization.

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George J. Hochmuth, Ed A. Hanlon, and John Cornell

Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] was grown at two sites differing slightly in Mehlich-I (double-acid) -extractable P (6 and 10 mg·kg-l soil). Early and total yields responded positively to P rate; however, maximum yields were obtained with small amounts of P fertilizer. The linear-plateau critical P fertilizer rates were 26 and 27 kg·ha-1 at sites 1 and 2, respectively. These critical rates were lower than those currently used for recommending P fertilizer on soils that have very low P. Phosphorus concentrations of most-recently matured leaves at early fruit set were 2.5 and 2.8 g·kg-1 at sites 1 and 2, respectively, with 0 P, and 4.4 and 4.8 g·kg-1 with the 25-kg P/ha treatment.

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S. Kuo

Acidifying soil to prevent annual bluegrass (Poa annua L.) from infesting creeping bentgrass (Agrostis palustris Hud.) reduces soil P and Ca availability. This study examined Ca and P effects on the growth of these two grasses in four moderately acidic soils using CaSO4 as a Ca source. Each soil received four P rates (0, 10, 40, or 80 mg·kg-1) and three Ca (as CaSO4) rates (0, 400, or 800 mg·kg-1). Neither Ca nor P treatments substantially changed pH or exchangeable soil Al. Clipping yields, tissue P concentration, and P uptake of both grasses were affected by soil NaHCO3-P levels. Compared to bentgrass, annual bluegrass had higher clipping yields and P uptake at high P rates or high NaHCO3-P levels; this result indicates that annual bluegrass was as acid-tolerant as the bentgrass, provided that available P in the soil is adequate. Adding CaSO4 to the Papac soil, which contained the least amount of exchangeable Ca among the four soils, markedly enhanced the clipping tissue P concentration and P uptake of creeping bentgrass but not those of annual bluegrass; this result indicates that a differential response to Ca existed between the two grasses. Maintaining an adequate soil Ca availability was necessary to improve bentgrass growth, particularly for the acid soil containing low available Ca initially.

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James E. Altland and M. Gabriela Buamscha

DFB to have low pH (3.7 to 4.4); little or no available nitrogen (N); relatively high water-extractable phosphorus (P; 10 to 28 mg·L −1 ) and potassium (K; 78 to 162 mg·L −1 ); low levels of calcium (Ca), magnesium (Mg), and sulfur (S); and moderate

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Robert O. Miller, Steven E. Newman, and Janice Kotuby-Amacher

The accuracy of soil and plant analytical results are occasionally called into question by laboratory clientele. Although laboratories generally conduct internal quality assurance procedures, there are few external performance testing programs for the industry. In 1994, a proficiency testing program was initiated for soil and plant samples for agricultural laboratories in the western United States to provide an external quality control for the lab industry. The program involves the quarterly exchange of soil and plant samples on which soil salinity, soil fertility, and plant nutrition analyses are conducted. One hundred laboratories are annually enrolled in the program from 24 states and Canadian provinces. Results of 3 years of the program indicate soil nitrate, soil pH, extractable potassium, soil and organic matter are reproducible within 10% between laboratories. Soil-extractable phosphorus (by five methods), soil-extractable boron, and soluble chloride were only reproducible within 15% to 20% between laboratories. Plant nitrogen and phosphorus results were consistent across samples, laboratories, and methods. Variability in plant nitrate increased with decreasing tissue concentrations. Overall accuracy and precision of reported results, based on the use of NIST certified reference botanical samples, were excellent for N, P, K, Ca, and Cu. Generally, for any given analysis, the results of ≈10% of the laboratories exceed two standard deviations from the mean. Overall, significant improvement was noted in the laboratory industry proficiency through the course of the program.

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James E. Altland, M. Gabriela Buamscha, and Donald A. Horneck

An experiment was conducted to determine how pH and nutrient availability in douglas fir bark (DFB) substrates respond to lime and sulfur (S) rates. The treatment design was a two-by-nine factorial arrangement with two substrate types and nine pH-altering amendments. The two substrates were 100% DFB or 75 DFB:15 sphagnum peatmoss:10 pumice (by volume). Substrate pH-altering amendments included elemental S amended at either 0.6 or 2.4 kg·m−3; calcium carbonate amended at 0.6, 1.5, and 5.9 kg·m−3; calcium hydroxide amended at 4.4, 8.9, or 23.7 kg·m−3; and a nonamended control. All substrates were amended by incorporating 0.9 kg·m−3 Micromax micronutrients before potting and topdressing 8 g/pot of 14N–4.2P–11.6K Osmocote controlled-release fertilizer after potting. A group of controls was also maintained for each substrate that received no fertilizer amendment (no S, lime, Micromax, or Osmocote). Four containers of each treatment were randomly selected and harvested 4 and 8 weeks after potting. Amendment with S decreased pH with increasing rate, whereas both lime types increased pH with increasing rate. The two substrates in general responded similarly to S and lime amendments, although there were some significant effects and interactions caused by substrate type. Ammonium-N and NO3-N both decreased exponentially with increasing substrate pH, whereas water-extractable phosphorus decreased linearly with increasing pH. Water-extractable potassium, calcium, magnesium, and sodium responded quadratically to increasing pH by initially decreasing and then increasing. The micronutrients boron and iron decreased with increasing pH, whereas DTPA extractions of manganese, zinc, and copper initially increased and then decreased over the range of observed pH.

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Alan L. Wright, Tony L. Provin, Frank M. Hons, David A. Zuberer, and Richard H. White

using a Model 700 Total Organic Carbon Analyzer (O.I. Analytical, College Station, TX) and for water-extractable phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) by ICP-AES (Spectro Analytical Instruments, Marlborough, MA

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David M. Olszyk, Tamotsu Shiroyama, Jeffrey M. Novak, Keri B. Cantrell, Gilbert Sigua, Donald W. Watts, and Mark G. Johnson

extractable phosphorus (EP) values were measured for four samples per biochar as discussed previously in Olszyk et al. (2018) . In brief, pH and EC were measured using a 2:1 water to biochar or soil ratio (v/v) with MilliQ water. The EP was measured

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Kirandeep K. Mann, Arnold W. Schumann, Thomas A. Obreza, and Jerry B. Sartain

) revealed a strong dependency of crop growth on soil chemical and physical properties. Sorghum shoot weight, radish shoot weight, and weed cover had significant positive relationships with organic matter, cation exchange capacity (CEC), Mehlich I-extractable

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Ka Yeon Jeong and James E. Altland

microbial immobilization. Fig. 5. The recovered water extractable phosphorus (P) from a substrate composed of 60 sphagnum peat: 30 bark : 10 perlite by volume. Data are expressed as mean percent of the total mass of 39.63 mg P applied via the controlled