Phosphorus Availability In Turfgrass Root Zones After Applications of Organic and Synthetic Nitrogen Fertilizers

Abstract

Organic fertilizers have increased in popularity over the past ten years due to the belief they are more environmentally sound to use than synthetic fertilizers. Most fertilizers derived from organic materials contain phosphorus as well as nitrogen, so use may be affected in states that legislate the application of P to lawns. States are considering exempting organic fertilizers from their zero‐P legislation, as Wisconsin did, because it is thought that P from organic sources is less likely to be lost in leachate or runoff. Fertilizers are applied on turfgrasses as needed based on N form and content. Many organic fertilizers contain as much P as N in their formulations, and therefore similar amounts of P and N are applied with each application. Soil tests in native soil and a fairway sand and peat mix used in the Pacific Northwest showed that organic fertilizers applied at rates to provide adequate N for acceptable turf increased soil Bray‐1 P levels from 16 to 18 mg/kg to 23 to 66 mg/kg within 3 years. Oxalate extractable Fe, Al, and P was determined for all treatments in both soils and used to calculate phosphorus saturation (PSIox). PSIox values from sand treated with one organic fertilizer source were significantly higher than measured in other treatments, indicating future risk of P loss with repeated applications of this organic fertilizer.

Influence of Dissolved Organic Carbon from Natural and Synthetic Fertilizers on Phosphate Leaching from a Sand‐Based Golf Green

“…Organic fertilizers exhibit slow N release characteristics as a result of their requirement for microbial decomposition and have been shown to offer some benefits in maintaining turf function (Tester et al, 1982; Landschoot and Waddington, 1987; Blume et al, 2009; Miller and Henderson, 2012). However, natural organic fertilizers derived from plant and animal by‐products or municipal biosolids may supply P in excess of plant demands when applied to meet N requirements (Liu et al, 1995; Maguire et al, 2000; Sims et al, 2000; Stahnke et al, 2013). Many organic fertilizers contain P in amounts approaching N, and therefore similar rates of P and N are applied.…”

“…Kerns (2004) reported leaching of PO 4 3− from composted dairy manure and municipal biosolids applied to various soils were only observed in root zones constructed according to USGA specifications; however, little risk for PO 4 3− leaching occurred during sod establishment if applications were P‐rate dependent. When applications of biosolids or composts are made based on plant N requirements, accumulation of P can occur in the surface soil (Cogger et al, 2001; Soldat and Petrovic, 2007; Stahnke et al, 2013). It has been suggested that high PO 4 3− losses from natural organic sources were most likely a result of high P application rate.…”