17 research outputs found
On-farm evaluation of a phosphorus site index for Delaware
The contribution of phosphorus (P) to non-point source (N PS) pollution of surface
and groundwaters is a serious environmental problem in Delaware. In 1999, the Delaware
Nutrient Management Act was passed limiting application of P on "high" P soils to a "three year
crop removal" rate or to the amount recommended by a University of Delaware P site index. The
Delaware P site index was developed and evaluated on seven farms in Delaware, through a joint
effort between the universities of Delaware and Maryland. Results showed that 78% of fields
evaluated were in the "low" risk category, with the remaining 22% falling into the "medium"
(6%), "high" (7%), and "very high" (9%) risk categories. The components of the index found to
have the greatest influence on P site index ratings were soil erosion, subsurface drainage,
leaching potential, distance from field to surface water, soil test P and organic P application rates
and methods. P site index ratings were found to vary by year, depending on manure
applications, suggesting a need for yearly P site index evaluations or averages over a cropping
rotation. The P site index worked well for identifying fields with differing relative potential risks
of P loss; however, validation of these P loss assessments is needed to ensure that the risk
categories assigned are sufficiently protective of water quality. Continual monitoring, analysis,
and improvement of the P site index are needed to ensure that it remains a useful tool for P
based nutrient management planning in the future
Determination of phosphorus source coefficients for organic phosphorus sources: Laboratory studies
Phosphorus losses in runoff from application of manures and biosolids
to agricultural land are implicated in the degradation of water
quality in the Chesapeake and Delaware Inland Bays. We conducted
an incubation study to determine the relative P solubility and bioavailability,
referred to as P source coefficients (PSCs), for organic P
sources, which are typically land-applied in the Mid-Atlantic USA.
Nine organic and one inorganic (ICH2PO4) P amendments were applied
to an Evesboro loamy sand (mesic, coated Typic Quartzipsamments)
at a rate of 60 mg P kri and incubated for 8 wk with subsamples
analyzed at 2 and 8 wk. There was an increase in Mehlich-3
P (M3-P), water-soluble P (WS-P), iron-oxide strip extractable P
(Fe0-P), and Mehlich-3 P saturation ratio (M3-PSR) with P additions,
which varied by P source. The trend of relative extractable WS-P,
Fe0-P, and M3-P generally followed the pattern: inorganic P > liquid
and deep pit manures > manures and biosolids treated with metal
salts or composted. We found significant differences in the availability
of P from varying organic P sources. The use of PSCs may be beneficial
when determining the risk of P losses from land application of manures
and other organic P sources and could be used in risk assessments
such as a P site index. These PSCs may also be useful for determining
P application rates when organic P sources are applied to P deficient
soils for use as a fertilizer source
Extração e exportação de nutrientes por variedades de cana-de-açúcar cultivadas sob irrigação plena
Determination of phosphorus source coefficients for organic phosphorus sources: Laboratory studies
Phosphorus losses in runoff from application of manures and biosolids
to agricultural land are implicated in the degradation of water
quality in the Chesapeake and Delaware Inland Bays. We conducted
an incubation study to determine the relative P solubility and bioavailability,
referred to as P source coefficients (PSCs), for organic P
sources, which are typically land-applied in the Mid-Atlantic USA.
Nine organic and one inorganic (ICH2PO4) P amendments were applied
to an Evesboro loamy sand (mesic, coated Typic Quartzipsamments)
at a rate of 60 mg P kri and incubated for 8 wk with subsamples
analyzed at 2 and 8 wk. There was an increase in Mehlich-3
P (M3-P), water-soluble P (WS-P), iron-oxide strip extractable P
(Fe0-P), and Mehlich-3 P saturation ratio (M3-PSR) with P additions,
which varied by P source. The trend of relative extractable WS-P,
Fe0-P, and M3-P generally followed the pattern: inorganic P > liquid
and deep pit manures > manures and biosolids treated with metal
salts or composted. We found significant differences in the availability
of P from varying organic P sources. The use of PSCs may be beneficial
when determining the risk of P losses from land application of manures
and other organic P sources and could be used in risk assessments
such as a P site index. These PSCs may also be useful for determining
P application rates when organic P sources are applied to P deficient
soils for use as a fertilizer source