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N, P and K: fertilizer management for oats

Oats yield was optimized when soil N plus fertilizer N was at 90 to 100lb/ac. Response to phosphorus (P) and potassium chloride (KCl) was minor in these trials.

November 19, 2007
By R.M. Mohr C.A. Grant and W.E. May


Oats production in the northern Great Plains has increased in recent years.
Production on the Canadian prairies currently accounts for more than half of
the total Canadian oats crop and exports.

Despite the growing prominence of oats in today's production systems, limited
research on fertilizer management for oats has been conducted in this region.
Fertilizers often account for a significant proportion of total input costs
in cereal production systems and may strongly influence crop growth, development,
yield and quality. Moreover, improved fertilizer management of oats may help
to enhance crop quality and thus the potential for producing high quality oats
that are suitable for more specialized milling and horse feed markets offering
price premiums.

A three year field study was initiated in 2000 with the objectives of determining
the effect of N, P and KCl on the growth, yield and quality of oats, and to
determine the impact of varying combinations of the nutrients. Field experiments
were established at two sites in the area of Brandon, Manitoba. One site was
located on a Newdale clay loam containing low levels of soil nitrate-N (NO3-N)
and extractable-P. The second site was located on a Stockton fine sandy loam
or Wellwood loam soil containing low levels of soil NO3-N
and higher extractable-P levels, but considered marginal based on soil test

Experimental treatments consisted of a factorial combination of four N rates
(zero, 36, 72, 108 pounds N per acre as urea), three P rates (zero, 27, 54 pounds
P2O5 per acre as mono-ammonium phosphate
– MAP), and two potassium (K) rates (0 and 36lb K2O
per acre as KCl). Each treatment received an additional 12lb N per acre as urea
or MAP in addition to the N rate indicated, to account for N supplied by the
highest P rate. An unfertilized control treatment was also included. Oats (cv.
AC Assiniboia) was direct seeded using a plot seeder equipped with hoe openers
on nine inch row spacing. At the time of seeding, urea and KCl were side-banded
and MAP was placed with the seed. Grain yield was determined by straight-combining
the entire plot and oats test weight, kernel weight and percentage of plump
kernels were determined.

Soil test nutrient levels at the trial sites ranged from low to medium for
N: eight to 15 parts per million (ppm) in the top 24 inches; low to sufficient
for P: four to 15ppm in the top six inches; and medium to sufficient for K:
113 to 246ppm in the top six inches. Soil nutrient analysis used an extraction
with NaHCO3. Nitrate-N was determined by hydrazine reduction,
P (PO4) was by molybdate/ascorbic acid, and K was by atomic
absorption. Grain yield responses were expected for N and P, while no response
was expected for K.

Low rates of fertilizer N were found to increase oats grain yields at all locations,
with the crop response levelling off or declining at higher rates. While maximum
oats yield was typically attained at the 36 to 72 pounds N per acre rate, the
optimum relative yield was achieved with a total of soil plus fertilizer N of
approximately 90lb N per acre (see Figure 1). In this study, optimum yields
ranged from 90bu/ac to 135bu/ac of oats. Nitrogen additions had the most consistent
impact on the grain quality of the oats crop. Increasing N rates always resulted
in a small but significant decline in oats test weight, kernel weight and the
percentage of plump kernels for both trial locations and all years.

Phosphorus application was found to increase oats grain yield at two of the
six trial site years (see Figure 2). This occurred despite an increase in early
season crop bio-mass yield at tillering with P application at both sites and
all years (data not shown). In addition, plant development assessment showed
that P application significantly advanced the developmental stage of the main
stem and tillers arising from the coleoptile (T0) and the first leaf (T1). The
observed crop response to fertilizer P application did not appear to be closely
linked to soil test P levels. The response to P addition in 2002 may reflect
the very dry spring soil moisture conditions, reducing the availability of soil
P to plants and contributing to the positive crop response to fertilizer P.
No consistent grain quality effects were observed with the application of P
fertilizer to the oats crop.

Potassium fertilizer use was found to provide a small but statistically significant
oats grain yield increase at one of the six trial locations (see Figure 2).
While a similar trend was observed at the two locations in 2000, these were
not significant. The use of KCl increased the plumpness of oats kernels at three
of the six locations (data not shown). The test weights of oats were also increased
at one of the six locations and decreased at another. While significant, these
grain quality differences were relatively small in magnitude. While interactions
among nutrients applied occurred in a number of instances, there was no strong
or consistent pattern.

The results of this study support previous research indicating that oats remove
less nutrients per bushel of production than many of the other crops grown on
the northern Great Plains. Nutrient removal in oats is approximately 0.5 to
0.8 pounds N per bushel, 0.23 to 0.28 pounds P2O5
per bushel, and 0.17 to 0.20 pounds K2O per bushel. While
fertilizer N additions increased oat yields, application in excess of rates
required to optimize yield should be avoided to maintain grain quality. Fertilizer
P additions improved early season plant development at all locations, and grain
yield at two of the six trials. Potassium fertilizer application resulted in
small improvements in both oats yield and quality. -30-

*Dr. Mohr is a sustainable systems
agronomist and Dr. Grant is a soil scientist with Agriculture and Agri-Food
Canada in Brandon, Manitoba. Bill May is an agronomist with Agriculture and
Agri-Food Canada in Indian Head, Saskatchewan. Reprinted from Better Crops with
Plant Foods, with permission of PPI/PPIC.


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