Date of Graduation

2014

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Horticulture

Committee Chair

Louis M McDonald

Committee Co-Chair

Thomas C Griggs

Committee Member

James Kotcon

Abstract

Phosphorus (P), an essential element for plants and animals, can be a limiting nutrient in organically-managed soils. To better understand P dynamics in organically-managed grasslands, P forms and availability in certified organic grasslands at the WVU Organic Research Farm were determined. The experimental design was a randomized complete block established in 2000 and has been maintained continuously with certified organic methods. We compared three Usage systems (Pasture, Buffer, and Hay) each at two levels of Fertility (High and Low). Phosphorus forms were determined by sequential fractionation with H2O, NaHCO3, NaOH and HCl. Extractable P was determined using several soil test procedures common to the Northeastern United States (Mehlich 1, Mehlich 3, Morgan, and Modified-Morgan). In addition, the physical and chemical properties soil texture, pH, EC, % carbon and aluminum (Al ox) and iron (Feox) oxides were determined. The soil characteristics measured showed no significant differences with respect to Usages or Fertility. Also, the interaction effect of Usages * Fertility was not significant. The results showed that extractable P determined using all four soil test procedures was low in all treatments, which suggests that the application of organically approved P-containing materials could increase forage production. Sequentially-extracted P followed the order NaOH-P > NaHCO3-P > HCl-P > H2O-P. It has been suggested that all of H2O extracted P and part of NaHCO 3 extracted P is available to plants. About half of the total soil P was extracted by the sequential procedure and about half of that was in the operationally-defined organic form. The results showed that the sum of extractable fractions of P ranged from 42 to 45 percent of total P. A significant portion of P is not extractable and is not available to plants. Also, among the available portion, only a small concentration of P exists in the soil solution in forms suitable for biological uptake. Thus, P may have relatively high total concentrations in soils but in many cases it is immobilized and becomes unavailable to plants. The Langmuir isotherm characterization showed that the soils from this grassland have high P sorption capacities. The reinterpretation of sorption/desorption data indicated that even when mineral P is added, much of that P is bound to the soil and very little P remains in soil solution. This suggests that the mineralization of organic P is a key factor maintaining the productivity of these soils.

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