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Fargo, ND, United States

Linquist B.,University of California at Davis | Ruark M.,Dep. of Soil Science
Agronomy Journal

The efficient management of P fertilizer in rice (Oryza sativa L.) systems is essential in ensuring optimal yields while also avoiding problems related to over application. Identifying P deficient soils is critical to developing efficient P recommendations. The objectives of study were to determine the extent of P deficiencies in California rice systems, evaluate diagnostic P tests, and identify soil P fractions that contribute to crop P nutrition. On-farm P-omission experiments were conducted at 64 sites where we measured Y-leaf P concentration, P uptake, and grain yield. Soil samples were collected and analyzed for Olsen and Bray-P as well as being subjected to a sequential P fractionation scheme to determine NaHCO3, NaOH, and HCl inorganic (Pi) and organic (Po) P. From grower interviews, an annual input/output P budget was constructed for each site that accounted for P fertilizer inputs and outputs (P removed at harvest) over the previous 5 yr. Olsen-P (critical value: 6 mg kg-1) and Y-leaf P tests (critical value: 0.2%) were reasonable at predicting P deficiencies across a wide range of soil types. The P budget, correlated with Olsen and Y-leaf P, was also helpful in determining if the grower applied P rates were adequate as the only P deficient sites had a P budget of 0.5 kg P ha-1 yr-1 or less. Sodium bicarbonate inorganic P (NaHCO3-Pi), NaOH-, and HCl-Pi and -Po fractions were all correlated with Y-leaf P concentrations. The only Po fraction correlated with Y-leaf P and the P budget was HCl-Po. The primary sinks for excess applied P fertilizer were the NaHCO3-Pi and NaOH-Pi fractions. © 2011 by the American Society of Agronomy. Source

Helms T.C.,Dep. of Plant science | Scott R.A.,U.S. Department of Agriculture | Schapaugh W.T.,Kansas State University | Goos R.J.,Dep. of Soil Science | And 2 more authors.
Agronomy Journal

Cultivar selection is one of the best ways to manage iron-deficiency chlorosis (IDC) problems in soybean [Glycine max (L.) Merr.]. The objective was to determine if precision farming techniques of planting IDC-tolerant cultivars in calcareous soil areas and high-yielding cultivars in non-IDC areas would increase soybean yield. We used paired sites within the same field. The sites were located in areas of a field where IDC was present and absent. The same commercial soybean cultivars were planted on the paired sites. Results showed that visual scores for IDC could not identify the highest-yielding cultivar in IDC-affected areas. If the only information available to growers is yield on non-IDC sites and visual IDC ratings, then the yield of the whole field could be increased by planting two different cultivars. If yield data from replicated performance testing of numerous different cultiars was available for IDC sites and also for non-IDC sites, then growers may be able to identify a single cultivar that has high yield across the entire field. © 2010 by the American Society of Agronomy. Source

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