Gd. Smith et al., Laboratory methods of estimating potentially mineralizable nitrogen in organic potting mixes. I. Development of incubation and chemical methods, COMM SOIL S, 32(17-18), 2001, pp. 2755-2768
Organic potting mixes supply plant nutrients through the mineralization of
organic matter. However, laboratory methods of estimating mineralization in
soilless potting mixes have not been developed. Using 100 potting mix form
ulations, this study investigated whether an anaerobic incubation method or
two chemical methods (alkaline KMnO4 and HCl) could be used to predict pot
entially mineralizable N (PMN) in organic potting mixes, using N uptake by
ryegrass herbage as the benchmark method of estimation of PMN.
The anaerobic incubation method failed to produce NH4+ from many mixes, and
was considered unsuitable as a PMN test. The alkaline KMnO4 and HCl method
s produced NH4+ in all cases, and correlation between net NH4+ production a
nd ryegrass herbage N was good (r = 0.66, P < 0.001 and r = 0.80, P < 0.001
, respectively). However, when initially available N was included with the
NH4+ produced by the tests, correlations with ryegrass herbage N were impro
ved (r = 0.95, P < 0.001 and r = 0.92, P < 0.001 respectively). It was conc
luded that the two chemical methods, modified to include initially availabl
e N, have potential as laboratory methods of estimating PMN in organic pott
ing mixes.