Phosphorus and nitrogen loading in manured Saskatchewan soils
Stumborg, C.M. 2006. M.Sc. Thesis. Dept. Soil Science, University of Saskatchewan, Saskatoon, SK
Abstract
The expansion of intensive livestock operations in western Canada has increased
the concerns about manure management practices that could adversely affect the
surrounding soil and water quality over an extended period of time. One significant
issue is the potential for nutrient transport off-site as it relates to excessive manure
application and nutrient loading. The objectives of this research study were to
determine the loading, migration and distribution of manure-derived phosphorus (P) and
nitrogen (N) in the soil, as affected by repeated manure application, and to determine the
ability of different measures of soil P: Total, Modified Kelowna, Olsen extractable,
water extractable, and Plant Root Simulator (PRS™
), to reflect soil P loading in the
soils.
Experiments were conducted at four Saskatchewan (SK) sites under long-term
manure management. Liquid hog manure (LHM) and solid cattle manure (SCM)
treatments were applied annually over eight years at Dixon (Black soil zone), while only
LHM was applied at Plenty (Dark Brown soil zone) and Riverhurst (Brown soil zone)
over six years, and at Melfort (Black soil zone) over five years. Soil samples were
collected in the spring and fall of 2003 and 2004 and were analyzed for soil labile P and
nitrate - N (NO3- - N) levels. Plant samples were collected in 1 m2 quadrats to determine
the impact of manure application rate on plant nutrient uptake.
The annual application of LHM (37,000 L ha-1 yr -1 ) and SCM (7.6 Mg ha -1 yr -1 )
at agronomic rates did not significantly elevate soil labile P or NO3- - N compared to the
unfertilized controls at all four SK sites. However, environmental conditions that
limited plant uptake and export of nutrients off-site, such as drought and nutrient imbalance, tended to enhance residual P and N levels, even at agronomic rates. High
application rates (111,000 L ha -1 ) applied once every three years at the Melfort site
resulted in no significant elevation of residual labile P and NO3- - N compared to the
control.
Excessive LHM rates (148,000 L ha -1 yr -1 ) applied annually caused soil
accumulation of residual P and N over time at Dixon, Plenty, and Riverhurst. At the
Dixon LHM site, deep leaching of NO3- - N was observed at excessive rates (148,000 L
ha -1 yr -1 ) up to the 150 cm depth, compared to the control. At Dixon, high annual
application rates of SCM (30.4 Mg ha -1 yr -1 ) did not significantly elevate NO3- - N
amounts in the surface soil (0- to 60-cm) compared to the control, which was attributed
to low mineralization of organic N from the SCM.
Total soil P analysis did not indicate a significant increase in P loading for any
rate of LHM or SCM, however, all four measures of labile P did indicate significant
changes with varying manure rate. All methods used to measure soil labile P fractions
were strongly correlated with one another at all sites (r > 0.803** at p = 0.01) except
Melfort, which had infrequent LHM applications and high organic matter levels that
may have skewed results. The strong relationship between soil test methods used for
making P fertilizer recommendations in western Canada (Modified Kelowna, Olsen
extractable, and PRS) with the water extractable method (environmental P indices),
indicated that the agronomic-based soil P tests would be effective in monitoring labile
soil P loading under long-term manure management as part of an early warning system
to detect build-up in residual P levels.
