Relating hydrometer readings to solids and phosphorus content of liquid... Results Introduction M.D. Timmerman,

Relating hydrometer readings to solids and phosphorus content of liquid pig manure
M.D. Timmerman, Agri-Environment Knowledge Centre, Manitoba Agriculture, Food and Rural Initiatives, Carman, MB R0G 0J0
Introduction
Results
Method
In early 2004, ~200 manure samples from more than fifty
operations were collected by a pig industry co-operator from three
types of operations: sow, nursery and finisher. Upon receipt by the
lab, samples were either immediately tested or frozen until analysis
could be performed. The samples were analyzed by Norwest Labs
(now Bodycote Testing Group) using i) a field test kit hydrometer
(Agros N Meter) to produce a standardized reading, ii) a laboratory
grade hydrometer to produce a specific gravity reading and iii) the
standard laboratory method to determine dry matter and P
concentrations. Hydrometer readings were taken after samples
were thoroughly mixed.
Results were analyzed by linear regression analysis as the
distribution of the data indicated that any detectable relationship
would be based on linearity.
Field Hydrom eter
2
R = 0.81
2
R = 0.76
10
8
6
4
2
0
0
2
4
6
8
10
12
F ield H y d r o m et er
12
40
60
80
Fig. 5. Field hydrometer readings vs. P2O5 - finisher data.
Results and Discussion
2
R = 0.64
10
20
P2O5 (lb/1,000 gal)
Dry Matter (%)
Fig. 1. Relationship b/w phosphorus and dry matter – pooled data.
The basis of the hydrometer test method for estimating P content of
liquid manure is the tendency for manure P to associate with the solids
portion. In the samples analyzed manure P concentrations were related
to dry matter content (Fig. 1).
8
6
4
2
0
0
20
40
60
80
P2O5 (lb/1,000 gal)
6
Zhu et al. (2003) found a very strong linear relationship between
hydrometer readings and total P (R2=0.97), however, it was for a single
source of nursery barn manure. The authors advised that individual
regression equations should be derived from operation-specific data. It
was also cautioned that error is likely to be larger at lower manure P
levels. However, this is only likely to be the case with very dilute
manure and agronomists are generally concerned with identifying highP manure that must be more carefully managed. Other research has
produced results that are more similar to those obtained in this study.
5
4
3
2
2
R = 0.69
1
0
0
20
40
60
80
P2O5 (lb/1,000 gal)
6
2
R = 0.21
4
Conclusion
Accurate, in-field analysis of liquid manure for P content would greatly
improve manure nutrient management where no extensive operationspecific data base is available and/or variability in liquid manure P
concentrations is large during pump-out. The results of this study
indicate some potential for using the hydrometer method to estimate
manure P content and obtaining general guidance in managing manure.
However, in order for an agronomist to confidently use the hydrometer
method in managing liquid pig manure P, site-specific relationships
must be established.
Fig. 3. Field hydrometer readings vs. P2O5 - sow data.
5
Field hydrometer readings related to manure P content as follows: for
the pooled data R2=0.64 (Fig. 2), for sow manure an R2 of 0.69 (Fig. 3),
for nursery an R2 of 0.21 (Fig. 4) and for finisher an R2 of 0.76 (Fig. 5).
Results for the lab hydrometer readings in relation to P content were:
for sow manure an R2 of 0.79, for nursery an R2 of 0.85 and for finisher
an R2 of 0.56 (data not shown). The pooled result for this relationship
was R2=0.58.
Fig. 2. Field hydrometer readings vs. P2O5 – pooled data.
F ie ld H y d r o m e t e r
Confirmation could then come in the form of laboratory test report
after the manure has been applied.
80
70
60
50
40
30
20
10
0
0
Field Hydrometer
Research conducted elsewhere has shown
that the hydrometer method holds promise
for estimating manure P concentrations
(Zhu et al. 2003). Its potential lies in the
relationships between a) manure P content
and dry matter and b) specific gravity
(measured using a hydrometer) and dry
matter. Since manure P tends to associate
with the solids fraction, a measurement
that is sensitive to dry matter changes
should reflect changes in P concentration as
well. If strong numerical relationships can
be established such that estimates of P
content can be confidently obtained,
manure application rates could be adjusted
in the field or, at the very least, manure P
loading could be monitored on-the-go and
adjustments made to minimize P
accumulation in soil.
P 2O5 (lb/1,000 gal)
12
Management of manure phosphorus (P) is
intensifying. One of the challenges facing
manure P management is the variability of
P content in liquid manure, both between
and within storage structures.
Management of phosphorus (P) in liquid pig
manure may be enhanced if a rapid field
test method is shown to be effective in
estimating P concentrations.
Acknowledgements
3
2
Elite Swine
Bodycote Testing Lab
1
0
0
20
40
P2O5 (lb/1,000 gal)
Fig. 4. Field hydrometer readings vs. P2O5 - nursery data.
60
References
Zhu, J., P.M. Ndegwa and Z. Zhang. Settling characteristics of nursery pig
manure and nutrient estimation by the hydrometer method. 2003. J. Env.
Sci. Health, vol. B38, pp. 379-390.