Agriculture Reference
In-Depth Information
Figure 9.4
. Soil inorganic N pools of nitrate and ammonium (µg N g soil
-1
) in MCSE sys-
tems for 1993-2010. Mean ± SE for all measurements during the period.
Biologically Based systems suggests that the leguminous cover crop may pro-
vide much of this timely input (Fig. 9.5). Residue placement can also better
ensure the timely mineralization of N from soil organic matter (Loecke and
Robertson 2009).
Manipulating N mineralization offers a primary opportunity to improve N syn-
chrony. Particulate organic matter (POM) measurements could be used to estimate
N mineralization if combined with information about the previous year's crop and
cover crop production (Willson et al. 2001). Permanganate Oxidizable Carbon
(POXC) has also been shown to be a quick and inexpensive assay for assessing
management changes associated with changes in the labile C pool, which can
reflect key processes such as N mineralization (Culman et al. 2012).
Nitrification
Autotrophic nitrification is the microbial oxidation of NH
4
+
to nitrite (NO
2
−
) by
ammonia oxidizers and then to nitrate (NO
3
−
) by nitrite oxidizers (Robertson
and Groffman 2015). In most soils, the NO
2
−
produced rarely accumulates as it
is quickly oxidized to NO
3
−
. Nitrification can also produce the gas nitric oxide
(NO) as a by-product of the chemical breakdown of hydroxylamine (NH
2
OH) dur-
ing NH
3
oxidation, and, when oxygen (O
2
) is limiting, produce both NO and N
2
O
