| Experiment 801: Wheat Grain Yield Response to NPK under Acid Soil Conditions, Haskell, OK | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Abstract
Many of the soils where winter wheat is
grown in northeastern Oklahoma are extremely acid and deficient in
phosphorus. Experiment 801
was established in the fall of 1977 to evaluate the long-term effects of
nitrogen, phosphorus and potassium fertilizer applications in continuous
winter wheat grown on an acid soil. Applied
P was expected to precipitate some of the Al in soil solution, especially
at the low soil pH levels where increased Al was expected at this site.
Applied P without N produced the highest grain yields from 1978 to
1987, and 1988 to 1997. Following
two consecutive years of applied lime (2240 kg/ha, 71% ECCE) to the entire
area, the highest yielding plots were those receiving both N and P.
The lowest yielding plots were those receiving only N.
In general, those plots with the highest yields had the lowest
grain %N at this site. This
suggests that yield maximums were not achieved since increased grain %N
has been found at N rates in excess of that required for maximum yields. Materials and Methods Experiment 801 was established in the fall
of 1977 under conventional tillage on a Taloka silt loam (fine-mixed,
thermic Mollic Albaqualf). This
trial along with 802, 803, and 804 was initiated by Dr. Robert L.
Westerman, Professor and Head of the Department of Plant and Soil
Sciences. Wheat has been
planted for 19 continuous years in 10 inch rows at seeding rates of 90
pounds per acre (rates increased when
planting was delayed). Fertilization,
planting and management dates are listed in Table 1. The experimental
design in this continuing experiment employs
a randomized complete block with four replications.
Fertilizer treatments and average grain yields for selected periods
are reported in Table 2. Individual plots at this site are 17 feet wide
and 50 feet long. The center
10 feet are harvested with a conventional combine the entire 50 feet in
length. In addition to wheat grain yield measured every year,
periodic soil and grain samples were taken for chemical analyses.
Results from surface (0-6 inches) soil samples collected in 1995
are reported in Table 3. Results Soil pH declined significantly in all plots
receiving N (with or without P and K). As a result, low soil pH (increased Al and Mn in soil
solution) is the controlling factor for wheat grain production at this
site. The lowest soil pH
values were also those associated with the highest NO3-N levels
in the surface. Applied P was
expected to precipitate some of the Al in soil solution, especially at low
soil pH levels where increased Al was expected.
Applied P without N produced the highest grain yields from 1978 to
1987, and 1988 to 1997. Applied
N did not result in any increased yield with or without P in the first
twenty years of the experiment. However,
following two consecutive years of applied lime (2240 kg lime/ha, 71%
ECCE), the combined application of N and P has resulted in the highest
yields. It was interesting to
find NO3-N levels in excess of 300 ppm in the surface six
inches. This translates into
over 600 lb N /ac that would be available. Over the 18 years from the time the experiment was initiated
to being soil sampled in 1995, accumulation of N was expected.
However, if leaching of excess N were a viable pathway over time,
surface accumulation at levels greater than the annual rate applied would
likely not be found. Increased
applied K (treatments 6, 7 and 8) tended to increase surface NO3-N. Table 1. Treatment applications and experimental management for continuous winter wheat Experiment 801, Haskell, OK, 1978-2000.
L
– lime applied at a rate of 2240 kg/ha (1 ton/acre) in July 1998 (71%
ECCE) Table 2. Treatment structure and wheat grain yields of long-term wheat Experiment 801, Haskell, OK, 1978-1997.
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