Illinois Fertilizer
Conference Proceedings
January 27-29, 1997
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S.A. Ebelhar and E.C. Varsa 1
Potassium (K) fertilizer placement and mixing within the soil Ap horizon can
influence its availability for plant uptake. Other factors affecting uptake
are root growth of plants, diffusion rate of K to roots, K fixation, environmental
conditions and tillage. Previous work by Kovar and Barber (1987) at Purdue
suggested the possibility for optimizing potassium uptake and utilization by
corn based on optimal placement and soil mixing of K fertilizers. Fertilizing
too large of a soil volume (i.e. broadcasting and mixing in the Ap horizon)
could result in the excessive fixation of K in soils which fix K. Fertilizing
too small of a soil volume may create a situation where the plant roots, which
occupy only about one percent of the soil volume, do not occupy enough of the
fertilized volume for optimal fertilizer utilization.
Farmers in Southern Illinois need to utilize no-tillage and reduced tillage
management practices on highly erodible land. This limits their ability to
mix fertilizer throughout the plow layer. For this reason, farmers need to
know how to best fertilize no-till areas to enhance optimum K uptake by plants.
By comparing different K placement methods we can determine if stratification,
low K utilization and reduced yields would warrant the periodic tillage of
these soils.
The objectives of this study are to:
1. Determine the placement method which optimizes potassium utilization for
corn and soybeans under no-till and reduced tillage systems.
2. Determine effects of using K in starter fertilizer.
3. Determine effects of potassium rate and placement on potassium uptake and
yields of corn and soybean.
4. Evaluate monthly sampling of selected plots at each location to measure
variance among samples and seasonal effects on soil test K values.
5. Determine soil K stratification after 3 years of K placements.
6. To include a final report at the conclusion of this project to address each
of the objectives stated above.
A field study was initiated in 1994 at the Dixon Springs Agricultural Center
(DSAC) and at the SIU Belleville Research Center (BRC). No-till (NT) and chisel
tillage (CT) treatments were used in a corn: soybean rotation. Prior to study
initiation, soil samples were taken from the top 8" of soil at each location.
The averages are shown in the table below. Lime, at a rate of 4 tons per acre
was spring applied to the DSAC site before tillage was performed in 1994. A
finely ground lime (54 % passed #60 mesh sieve) was chosen for quick reaction.
Soil test levels (0-8" samples) at DSAC and BRC at start of study.
| Location |
1994 Crop | pH | P1 | K | Ca |
Mg | CEC |
|
|---|---|---|---|---|---|---|---|---|
| lb/acre | lb/acre | lb/acre |
lb/acre | meq/100g |
||||
| DSAC | Corn | 4.9 | 30 | 192 | 545 | 114 | 4.6 | |
| Soybeans | 4.6 | 26 | 250 | 177 | 125 | 4.1 | ||
| BRC | Corn | 7.1 | 56 | 194 | 3286 | 351 | 10.3 | |
| Soybeans | 6.9 | 74 | 249 | 3604 | 463 | 11.8 | ||
1996 Study. Chisel tillage was performed at DSAC and BRC in mid-May. Some
delay was due to excess precipitation received during late April and early
May. Tillage systems were blocked (whole plots) within each replication. A
factorial arrangement of K rates and K placements plus a zero K check (subplots)
were randomly placed within each tillage block in a split-split plot design.
K rates consisted of 60, 120 and 1801bs K20 per acre. K placement methods consisted
of surface broadcast (BC), 8-10" surface band (BD) over intended row,
surface dribble (DR) 6"
to side of intended row, and starter (ST). The starter treatment placed 301bs
of K20 2" to the side and 2" below the seed and was applied at planting.
The remainder of the K rate with the starter treatment was surface broadcast.
These treatments were applied to both corn and soybeans at DSAC and BRC with
4 replications per crop per location. In addition, Mg was surface broadcast
at DSAC at a rate of 36 lb/acre to alleviate possible low Mg supply in the
soil.
The K treatments were applied in solution form by dissolving potash (0-0-60)
in water. The treatments were applied after chiseling but before secondary
tillage to provide some mixing of the fertilizer with the tillage treatment.
In 1995 and 1996 a power tiller was used to incorporate the fertilizers. This
power tiller worked very well at incorporating the bands vertically with little
spread horizontally. Corn (Pioneer 3335 variety) was planted on 24 May at DSAC
and 31 May at BRC at a seeding rate of 26,000 seed acre. Soybeans (Pioneer
9451 variety) were planted on 4 June at DSAC and 31 May at BRC at a planting
rate of 10 seeds per foot in 30" rows (175,000 seeds per acre). Both the
corn and soybeans were replanted at BRC on 21 June due to poor stands created
by excessive rains in early June (Figure 7).
Phosphorus fertilizer was broadcast across all plots prior to planting. Nitrogen
was sidedressed on corn at a rate of 1501bs N/acre at 4 weeks after planting.
When starter N was applied, the sidedress N rate was adjusted accordingly.
Whole plant corn samples (from check plots and 1201b K20 rates)
were sampled between the 6 and 8 leaf growth stage and whole soybean plants
were sampled at about 12 inches of top growth from selected plots. These plants
were weighed in the field, transported to the lab, dried and weighed again
in order to determine a wet weight, dry weight and % moisture. After drying,
plants were ground and analyzed for nutrient concentrations (%). Nutrient contents
were determined by multiplying nutrient concentrations (in decimal form) by
dry weights. Corn ear-leaves were sampled from each plot at mid-silking and
uppermost fully developed trifoliate leaves of soybeans were sampled at mid
bloom for nutrient analysis. Grain yields, grain moisture, and final plant
stands were measured after physiological maturity.
Since the start of the study in 1994, soil samples have been taken each month
from the 120 lbs K20/acre plots along with the check plots for each crop at
each location. These samples are analyzed for pH, P, K, Ca, and Mg levels.
Because much of the interactions between K rates, K placement and tillage
are not significant, only main effects will be included in the discussion.
BRC Corn Results
K rate effects. There was a significant increase in corn grain yields
as K rates increased (Table 1), especially
with the first increment. Grain moisture increased slightly with K rates, but
plant stands and ear-leaf nitrogen were unaffected. Increasing K rates significantly
increased ear-leaf K concentrations while decreasing Mg levels. There is an
antagonistic relationship between K uptake and Mg uptake. The Mg levels were
approaching a critical level especially with high K rates. No visual Mg deficiency
symptoms appeared in the field. The zero and 601b K20 treated corn had leaf
K levels below the sufficiency range of 1.8 to 3%.
K placement effects. K placement had no significant effect on corn yields,
plant stands, and ear-leaf nitrogen (Table
2 and Figures 1 and 2),
but all had greater yields than the check. Grain moisture differences existed
but were small. There were no differences between placement methods for ear-leaf
K and Mg concentrations, but all placement methods were significantly different
from the checks. In the case of leaf K, the check had a lower concentration
(by 0.4 %) than the various placement methods. For the Mg levels, the checks
were significantly higher. There was a significant decrease in yield at the
higher K rates with no-tillage (Figure 2).
The worst case was with the banded treatment. After three years of applying
high rates of K fertilizer in localized bands, there appears to be a negative
effect on grain yields, perhaps due to salt injury.
Whole plant data. Fertilizer K placement significantly increased whole
plant wet weights, dry weights, moisture, % K, and K contents above the check
treatments (Table 3). There were significant
differences between placement methods for whole plant wet weight, dry weights,
N content and K contents. N and K contents are determined by multiplying the
dry weight by the respective concentration (%). The banded treatment appeared
to have the best early growth even with no-till, but then had the poorest yields.
Perhaps the early growth advantage enjoyed by the banded treatment led to problems
down the road, or perhaps the salt injury occurred later in the season as drought
conditions occurred (July and August, Figure
7). As in 1995, the broadcast K treatment had the lowest K concentration.
This is an indication that the broadcast treatment was not as efficient in
getting K into the plant early. By silking there was no difference in the leaf
K concentrations.
Starter nitrogen. A starter nitrogen plus potassium treatment was added
to compare with the starter K treatment without N. At BRC, the nitrogen in
the starter failed to increase grain yields or K uptake as measured by % K
in whole plants and ear-leaves (Table 4).
There were significant increases in whole plant wet weights, dry weights, %N,
and N content. By silking, there were no differences measured by the ear-leaf
concentrations of N or K. Replanting in June into warm soils may have diminished
effects of starter N.
DSAC Corn Results
K rate effects. As at BRC, increasing K rates at DSAC significantly
increased yields, and earleaf K while decreasing ear-leaf Mg concentrations
(Table 5). With yield, there was a significant
increase with K above the check, but no increase in yield occurred above the
60 lb rate. Mg levels in the ear-leaves were double the levels in 1995 and
were now above what's normally considered a critical range for ear-leaf Mg.
This is attributed to the fertilizer Mg applied to the area in 1996, however,
Mg levels still decreased with increasing K rates, but not below critical plant
levels. The leaf N and K levels are within the sufficiency range for corn,
except for the checks.
K placement effects. The main effects of placement method for K had
no significant effect on grain yield, grain moisture, or ear-leaf N, K and
Mg concentrations (Table 6 and Figure
3). There was a significant increase in yield for the 1201b Kz0 rate when
banded both for CT and NT (Figure 3).
Apparently there was some benefit from the surface banding, but this effect
is opposite that which occurred at BRC.
Whole plant data. Differences between placement effects on whole plant
wet weights and dry weights and moisture were small but significantly better
than the check treatments (Table 7). The
effects of K rates were more pronounced than the effects of placement, especially
in regards to K concentrations and contents.
Starter nitrogen. As at BRC, starter treatment effects at DSAC were
small. Only N concentrations in whole plants were significantly higher with
N in the starter than without (Table 8).
Again, the lateness of planting may have played a role in the response to starter
N.
BRC Soybean Results
K rate effects. Grain yields, grain moisture and trifoliate N concentrations
were unaffected by K rates (Table 9). Increasing
K rates increased trifoliate leaf K concentrations while decreasing Mg.
K placement effects. K placement had little or no significant effect
on either grain yields or moisture (Table
10 and Figure 4). Again the importance
of K rate (especially above the check treatment) was more critical than the
impact of K placement.
Whole plant data. Whole plant wet and dry weights and moisture were
relatively unaffected by K placement (Table
11). Moisture contents, K concentration, and K contents were higher with
K placement than check plots but Mg concentrations and contents were lower.
Starter nitrogen. The N added to the starter increased early season
growth but failed to provide any significant yield benefit. Adding N to the
starter treatment increased whole plant wet weights, dry weights, N contents
and K contents (Table 12), especially
with no-tillage. N and K concentrations were unaffected by addition of N to
the starter.
DSAC Soybean Results
K rate effects. Applying fertilizer K increased soybean above the checks
at DSAC in 1996 (Table 13). The highest
yield occurred at the 601b K20 rate and declined at the highest rate. Increasing
K rates increased leaf K concentrations and decreased Mg. K rates had no effects
on grain moisture or leaf N.
K placement effects. Banding increasingly higher K rates decreased yields
(Table 14 and Figure
5) especially with CT (Figure 6).
This may be another indication of salt-type injury to soybeans where high K
rates have been applied and incorporated in close proximity to the seed. Grain
moisture was relatively unaffected by K placement. The very dry August (Figure
7) experienced at DSAC in 1996 may have resulted in the salt injury to
soybeans that led to yield losses.
Whole plant data. Addition of K fertilizer increased whole plant moisture,
K concentrations, and K contents (Table 15),
but did not affect wet or dry weights.
Starter nitrogen. There was no significant increase in yields with starter+N
treatments and little or no benefit to early season growth (Table
16). Only whole plant N concentrations were affected.
Monthly Soil Samples
Data not summarized yet.
Increasing K rates (especially above the check) seemed to increase early plant
growth and yields for corn more so than soybeans. Corn usually requires more
K which would explain its responsiveness to K. The placement method of K has
not been that critical, even for no-till for these first two seasons. Some
problems occurred in 1996 with the long term banding of K fertilizers in 10" bands
over the intended rows. This is in contrast to a yield benefit from . banding
at other locations or crops. Weather problems of a wet spring followed by very
dry conditions late in the season may have contributed to the results in 1996.
What's next:
We will continue to monitor the soil on a monthly basis through May of 1997.
This data will be summarized during the next year. In April 1997, we will take
soil samples in vertical increments (every 3 ") and in horizontal increments
(every 2" across two corn rows) to obtain a profile of the placement effects
on soil stratification both vertically and horizontal.
We will also begin to analyze and summarize the data across years. A final
report should be finished by next December.
Table 1: Potassium rate effects on corn yields, grain moisture and ear-leaf nutrients at BRC, 1996
Table 3: Potassium placement effects on whole corn plants (WP) at BRC, 1996
Table 4: Starter N effects on corn yield, whole plants (WP), and ear-leaves (EL) at BRC, 1996
Table 5: Potassium rate effects on corn yields, grain moisture and ear-leaf nutrients at DSAC, 1996
Table 7: Potassium placement effects on whole corn plants (WP) at DSAC, 1996
Table 8: Starter N effects on corn yield, whole plants (WP), and ear-leaves (EL) at DSAC, 1996
Table 11: Potassium placement effects on whole soybean plants (WP) at BRC, 1996
Table 15: Potassium placement effects on whole soybean plants (WP) at DSAC, 1996
Figure 1. Corn grain yields at BRC averaged across tillage, 1996
Figure 2. Corn grain yields at BRC under no-tillage, 1996
Figure 3. Corn grain yields at DSAC averaged across tillage, 1996
Figure 4. Soybean grain yields at BRC averaged across tillage, 1996
Figure 5. Soybean grain yields at DSAC averaged across tillage, 1996
Figure 6. Soybean grain yields at DSAC under chisel tillage, 1996
Figure 7. Rainfall and normal rainfall for DSAC and BRC, 1994-96
1 Agronomist, Univ. of Illinois, DSAC, Simpson, IL and Assoc.
Prof. SIUCarbondale, Carbondale, IL.
Kovar, J. L., and S. A. Barber. 1987. Placing Phosphorus and Potassium for
Greatest Recovery. J. Fert. Issues 4:1-6.
