Estimation of In-season Nitrogen Mineralization in Irrigated Potato

Estimation of In-season Nitrogen Mineralization in Irrigated Potato
Production Systems in Manitoba using a Nitrogen Balance Approach
Ramona
1
Mohr ,
Dale
2
Tomasiewicz ,
Alison
3
Nelson ,
Cynthia
1
Grant ,
Bernie
4
Zebarth and
Gordon
1
Finlay
1Agriculture
and Agri-Food Canada, Brandon, Manitoba; 2Canada-Saskatchewan Irrigation Diversification Centre, Outlook, Saskatchewan; 3Canada-Manitoba Crop
Diversification Centre, Carberry, Manitoba; 4Agriculture and Agri-Food Canada, Fredericton, New Brunswick
Introduction
• In-season mineralization of soil nitrogen (N) has the
potential to contribute significantly to the plantavailable N supply in irrigated potato (Solanum
tuberosum L.) systems.
• Little information is available regarding the quantity of
N mineralized under irrigated potato in Manitoba;
however, limited responses to N fertilizer in some field
studies with low to medium soil test N levels suggest
that considerable N mineralization may occur.
The objective of this study was to quantify in-season N
mineralization across Manitoba’s potato-growing region
using a N balance approach.
Materials and Methods
Field experiments were conducted at various sites across
southern Manitoba from 2006 through 2012 to assess inseason N mineralization under irrigated potato (cv. ‘Russet
Burbank’). The sites selected varied in geographic
location, texture and soil organic matter (Table 1).
Table 1. Soil characteristics at experimental sites
(0-15 cm depth), averaged across study years
Site
Carberry
Carberry
Portage
Shilo
Winkler
a
b
Study years
2006-2009
2010-2012
2007-2009
2006-2008
2006-2009
Texturea
Organic Cb Total Nb
-----g kg-1----loam
29.7
2.7
sandy loam
14.0
1.4
clay loam
41.5
3.8
sandy loam/loamy sand
21.9
2.3
sandy loam
17.8
1.8
At each site, soil samples were collected in spring prior
to crop establishment, and in fall following potato harvest,
in increments of 0-15, 15-30 and 30-60 cm. Whole plant
samples were collected immediately before harvest, or
earlier if crop senescence became evident. KCl-extractable
NO3 concentration in soil was determined by hydrazine
reduction, and total N in plant tissue by combustion. Soil
bulk density was measured in all years except 2006.
Net N mineralization was calculated as the difference
between total plant-available N at harvest (plant N uptake
+ soil NO3-N content to 60 cm) and spring soil NO3-N
content to 60 cm.
Results and Discussion
• In most site-years (14 of 17), in-season N mineralization
ranged from about 70 to 125 kg N ha-1 (Figure 1).
• Nitrogen mineralization at a given site often fell within
a relatively narrow range regardless of year (Figure 1).
• Mineralization averaged 97, 91, 130, 95 and 88 kg N
ha-1 at the Carberry loam, Carberry sandy loam,
Portage, Shilo and Winkler sites, respectively.
• Regression analysis of site means (mineralization
averaged across years within a site) indicated that
84% of variability among sites was related to surface
soil organic matter concentration (data not presented).
• The quantity of N mineralized during the growing
season generally increased with increasing total N
concentration in the surface soil (Figure 2).
Figure 2. Relationship between in-season N
mineralization under irrigated potato and total N
concentration in the surface 0-15 cm of soil
• In the current study, an additional 16 kg N ha-1 was
mineralized for every 1 g kg-1 increase in soil total N
concentration (0-15 cm depth).
• Total N concentration in the surface soil accounted
for 46% of the variability in N mineralization among
site-years. Factors such as weather conditions may
also have affected mineralization and its estimation.
Agriculture and Agri-Food Canada, Brandon Research Centre, Grand Valley Road, Brandon, Manitoba R7A 5Y3 Email : [email protected]
• Estimates based on a N balance approach indicated that
N mineralization in irrigated potato systems typically
contributed from 70 to 125 kg ha-1 of plant-available N
during the growing season.
• Factors that may contribute to relatively high N
mineralization under irrigated potato crops as compared
to other annual crops include: consistently moist soil
conditions under irrigation, intensive tillage pre-plant
and at hilling, and a longer growing season than most
other annual crops.
*The linear relationship indicated is based on all site-years, except Winkler 2007 and 2008,
which were considered outliers (shown as red squares).
*Error bars indicate +/- one standard deviation.
Conclusions
• Higher amounts of in-season N mineralization were
generally associated with soils containing a higher soil
organic matter concentration in the surface horizon.
Figure 1. Estimated in-season N mineralization
under irrigated potato in Manitoba (2006-12)
Texture was determined by hydrometer method.
Organic C and total N were determined by combustion.
In the year prior to potato, sites were cropped to a
cereal or oilseed except Portage 2007 which was
cropped to alfalfa/clover. Spring soil NO3 ranged from
13 to 83 kg ha-1 to 60 cm at all sites but Winkler 2008.
Experiments were arranged in a randomized
complete block design with 4 to 5 replicates, with N
mineralization determined in one treatment receiving
no N fertilizer.
• Estimated N mineralization was most variable at
Winkler, ranging from 15 kg N ha-1 in 2008 to 166 kg N
ha-1 in 2007. This may reflect, in part, limitations of the
N balance approach as well as variability within the site.
• In 2007, plant N uptake was generally higher and
more variable than in other years. In part, N uptake
from below 60 cm may have contributed to the plant
N supply thus increasing apparent N mineralization.
• In 2008, high spring soil NO3 levels (156 kg ha-1 to
60 cm) and excess rainfall likely contributed to N
losses that reduced estimated N mineralization.
• Total tuber yield in 0N treatments ranged from 27 to 52
Mg ha-1 at study sites. Fertilizer N increased (P≤0.10)
yield in 9 of 17 site-years although soil test guidelines
would have recommended N fertilizer in most cases.
• Nitrogen mineralization contributes significantly to the
plant-available N supply in irrigated potato systems, and
thus may impact N cycling and crop responses to N
fertilizer in these systems.
Acknowledgements
Support for this research was provided by Agriculture and
Agri-Food Canada and the Canada-Manitoba Crop
Diversification Centre (CMCDC). Technical expertise was
provided by Desiree Czerkawski, Shirley Neudorf and
Gord Finlay at AAFC-Brandon, and by the staff at
CMCDC Carberry, Portage and Winkler sites.