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Agronomy Journal Abstract -

Effect of Partially Acidulated Rock Phosphate and Concentrated Superphosphate on Yield and Chemical Composition of Alfalfa and Orchardgrass1


This article in AJ

  1. Vol. 65 No. 2, p. 286-289
    Received: July 21, 1972

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  1. J. A. Lutz Jr.2



Data from field experiments on the relative efficiencies to alfalfa (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.) of partially acidulated rock phosphate (PARP) and fully acidulated rock phosphate (CSP) is limited and additional information on this subject is needed. Crop response to sulfur has been obtained in certain southeastern states and more information is needed to determine if continued cropping with the use of sulfur-free fertilizers may result in sulfur-deficient areas in Virginia.

Florida rock phosphate was acidulated with H3PO4 at 20 and 100% of that required to convert rock phosphate to concentrated superphosphate. These two materials plus a check (O P) were applied as treatments for alfalfa and orchardgrass during 3 consecutive years in field experiments. Rates of total P for each crop were 0 and 100 kg/ha. The orchardgrass also received 25 kg/ha total P from CSP. The alfalfa received either 140 or 280 kg/ ha K from KCl or K2SO4. The orchardgrass, in addition to P fertilization, received N from NH4NO3 at rates of 168 and 280 kg/ha and K from KCl or K2SO4 at the rate of 140 kg/ha.

Both crops responsed to P fertilization each year. In each of the 3 years with alfalfa and during the last 2 years with orchardgrass the PARP was as effective as CSP. Added S did not significantly increase alfalfa yields but did cause a highly significant increase in orchardgrass yields in the last year of the experiment. The N concentrations of both crops were significantly affected by P sources, while the higher rate of N significantly increased the N concentration of orchardgrass. Average P concentrations in both crops were higher with CSP. The K concentration in orchardgrass was significantly affected by P source in 1969 and 1970 but not in 1971. The K concentration of alfalfa was significantly affected by source and rate of K. The S concentration of alfalfa was significantly affected by source and rate of P and K. The S concentration of orchardgrass was significantly increased by the higher rate of N and by K2SO4.

When both experiments were concluded significantly higher amounts of available P were present in the 0- to 15-cm soil depth where PARP was applied.

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