Published online 11 April 2006
Published in Agron J 98:430-435 (2006)
DOI: 10.2134/agronj2005.0050
© 2006 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Papers
Tillage and Phosphorus Management Effects on Crop Production in Soils with Phosphorus Stratification
Gregory J. Schwaba,*,
David A. Whitneyb,
Gary L. Kilgoreb and
Daniel W. Sweeneyc
a Dep. of Agronomy, Univ. of Kentucky, N-122 Agricultural Science Bldg.-North, Lexington, KY 40546-0091
b Dep. of Agronomy, Kansas State Univ., 2004 Throckmorton Plant Sciences Center, Manhattan, KS 66506
c Southeast Agricultural Research Center, Kansas State Univ., Box 316, Parsons, KS 67357
* Corresponding author (gjschw2{at}uky.edu)
Received for publication February 13, 2005.
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ABSTRACT
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Reduced- and no-tillage seedbed preparation methods coupled with broadcast P applications lead to an accumulation of available P in the surface 0- to 5-cm soil layer and a depletion of available P deeper in the profile. A 3-yr study determined the effects of tillage and fertilizer P management on P uptake and grain yield for P-stratified soils. Tillage practices were moldboard plow (once at the start of the study followed by reduced tillage), reduced tillage (disk followed by field cultivation), and no-tillage. Four P management methods were imposed: (i) no P; (ii) 20 kg P ha–1 applied as a surface broadcast; (iii) 20 kg ha–1 applied as a banded starter, 5 cm to the side and 5 cm below the seed; or (iv) 20 kg ha–1 applied in a deep placed band, 13 to 15 cm on 0.7-m centers. The one-time moldboard plowing produced higher early season dry matter yields for corn (Zea mays L.), wheat (Triticum aestivum L.), and soybean [Glycine max (L.) Merr.] compared with the no-tillage system, but tillage effects on final grain yield were inconsistent. Subsurface placement of P generally increased P uptake and grain yield of corn and sorghum [Sorghum bicolor (L.) Moench], but had little effect on grain yield of soybean. Results indicate that subsurface applications of P fertilizers should be considered if soil test P is highly stratified within the surface 0- to 15-cm layer and the 15-cm composite is medium or below for available P.
Abbreviations: BC, broadcast • CK, check • DB, deep bands • NT, no-till • PL, plow • RT, reduced till • ST, starter • STP, soil test phosphorus • UAN, urea ammonium nitrogen
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INTRODUCTION
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IN southeast Kansas, available soil P concentration by the Bray 1-P method (STP) is frequently two to three times higher in the surface 0- to 5-cm than in the 5- to 10-cm layer, and some soils exhibit as much as 10 times more available P in the 0- to 7.5-cm compared with 7.5- to 15-cm layer (Fig. 1
). This buildup of soil test P is termed P stratification and is related to surface applications of P fertilizer in conjunction with seed bed preparation methods that do not completely invert the soil (no-till, reduced-till, and chisel/disk systems). Many studies have documented P stratification and the rate at which P stratification occurs within reduced tillage systems (Crozier et al., 1999; Blevins et al., 1983; Lataw et al., 1984). However, these studies did not assess the effects of P stratification on crop growth or yield or P management methods to reduce the impacts of P stratification.
Recent P placement studies have found some benefits to P stratification. In Indiana, Holanda et al. (1998) found early season root length density of corn and soybean in the 0- to 5-cm layer was greater for plants grown in no-tillage compared with conventional-tillage systems. The increased growth was attributed to higher P and water availability in the surface layer of the no-till cropping system. Similar results were observed on the Georgia Coastal Plains (Hargrove, 1985), where a study examined P placement effects on crop yield within conventional (moldboard plow followed by disk and field cultivation) and no-till cropping systems. Results showed no yield advantages to deeper placed P for either tillage system and found yields to be higher in the no-till system because of the increased water availability.
A study conducted at 26 locations in Iowa to determine optimum P and K placement for no-till corn found no significant yield response to starter or deep banded P regardless of the level of P stratification (Bordoli and Mallarino, 1998). Yield increases as a result of P application were only observed for sites with 11 mg P kg–1 or less in the surface layer (0–7.5 cm). In a separate study, no-till soybean yield frequently increased as a result of P fertilization when STP in the 0- to 7.5-cm layer was <13 mg P kg–1 or when the 0- to 15-cm depth was <9 mg P kg–1 (Bordoli and Mallarino, 2000). Only one out of seven P responsive sites had a significant yield increase to deeper placed P fertilizer compared with the same rate applied as a surface broadcast.
In Kansas, the effects of fertilizer P management in stratified profiles on crop growth and grain yields have not been studied. Considering the widespread observed P stratification in southeast Kansas soils and very low levels of STP in the subsoil, combined with periods of short-term drought common to the region, it is hypothesized that plowing to redistribute P in conjunction with deeper P placement will result in increased early season crop growth and improve grain yields. The objectives of this study were to measure the effects of tillage and annual P fertilizer management on plant growth parameters: early season dry matter production, early season P uptake, and grain yield for crops grown on stratified soils. The study was conducted on cooperators' land maintaining their current crop rotations. Crops studied were corn, winter wheat, soybean, and grain sorghum.
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MATERIALS AND METHODS
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Plot Establishment and Cultural Practices
Three sites in Bourbon County Kansas were established in the spring of 1997. Sites with at least twice the available P in the surface 7.5 cm compared with the 7.5- to 15-cm depth were selected so that experimental sites would represent soil conditions commonly observed in this region. Sites were resampled at 5-cm increments before starting the study. All selected sites had been in reduced tillage (disc and field cultivation) for several years before initiation of the study. Site 1 is mapped as a Parsons silt loam (fine mixed, thermic Mollic Albaqualfs), and Sites 2 and 3 are mapped as Catoosa silt loams (fine-silty, mixed, thermic Typic Argiudolls). All sites were in soybean production in the previous year (1996). Crop rotations and other cultural practices employed during the study were determined by the cooperator and are listed in Table 1. Results from Site 1 for 1999 are not reported due to poor plant emergence.
A split plot design with four replications (48 plots) was used at all sites. Three tillage practices were the whole plots and P fertilizer management was the subplot factor. Tillage practices were no-till (NT), reduced till (RT), and plow (PL). Reduced tillage consisted of spring disking and field cultivation to a depth of about 10 cm. The PL system consisted of a one time moldboard plowing (spring 1997) to a depth of 23 cm. In subsequent years, reduced tillage was used on plowed treatments to assess the residual value of moldboard plowing. Subplots were (i) 0 kg P ha–1 (CK), (ii) 20 kg P ha–1 as ammonium polyphosphate (10–34–0) applied as a surface broadcast (BC), (iii) 20 kg P ha–1 applied as a starter (ST) 5 cm to the side and 5 cm below the seed, and (iv) 20 kg P ha–1 applied in deep bands (DB), 15 cm deep and 0.7 m apart. Broadcast applications were made before plowing and before disking in the tilled treatments.
All crops with the exception of wheat were planted using a John Deere (Moline, IL) 1750 Conservation planter capable of applying both dry and liquid fertilizer in the starter position. Plot consisted of eight rows 9.12 m in length and 0.76 m apart. For wheat, the cooperators equipment was used to plant, which did not have starter placement capabilities. For this reason, starter P was not a treatment in the wheat study.
Nitrogen (13 kg N ha–1 UAN) was applied as a starter to all check plots to balance N fertilizer with P treatments. Except when soybean was grown, additional N fertilizer (UAN) was surface broadcast to the entire study area at the rate recommended by Kansas State Soil Testing Laboratory for each crop (Whitney, 1983). Initial soil test results indicated K was optimum so no K fertilizer was applied to any of the sites in the first year. Potassium deficiency was observed in the no-till treatment early in the first growing season, so 37 kg K ha–1 (potassium chloride) was applied as a starter (5 cm to the side and 5 cm below the seed) to all plots in subsequent years. Glyphate was applied to all NT plots before planting; other herbicides applied for weed control depended on weed pressure and cooperator discretion. Excellent chemical weed control was obtained at all locations, and post-emergence cultivation for weed was not performed or necessary of any of the treatments.
Plant Analysis
Six whole plants were collected from each plot at the V6 growth stage for corn and sorghum. Whole plant samples were taken at early boot for wheat and V3 growth stage for soybean by harvesting 0.45 m of row. All plant samples were dried at 60°C and weighed to determine dry matter production. The samples were then ground and a subsample retained for nutrient analysis. Corn, soybean, and sorghum grain yield was measured by hand harvesting a center row, and wheat grain yield was determined by harvesting a 46 cm wide strip from the center of each plot. Grain subsamples for each plot were retained for moisture determination and yield was corrected to a constant moisture level. Nitrogen, P, and K concentration of all plant samples were determined using H2SO4–H2O2 digestion (Linder and Harley, 1942). The concentration of N and P in each digest was determined colorimetrically (Technicon Industrial Systems, 1976) and K concentration was determined using atomic emission spectroscopy.
Dry matter, P uptake, tissue P concentration, yield, and nutrient concentration of the grain were statistically analyzed using the ANOVA and GLM procedures for a split plot design with four replications (SAS Institute, 1985). Means were separated with Fisher's protected LSD using a probability of 0.05.
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RESULTS AND DISCUSSION
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Initial soil test P distribution with depth for each site is listed in Table 2. Surface (0–5 cm) STP was low for Sites 1 and 3 and medium for Site 2. Subsurface (10–30 cm) Bray 1-P was very low at all sites. Considering the average 0- to 15-cm STP concentration, fertilizer recommendations are 25, 15, and 25 kg P2O5 ha–1 for Sites 1, 2, and 3, respectively (Leikam et al., 2003). At all sites, plowing effectively redistributed STP in the surface 15 cm. Figure 2
shows this effect at Site 3.
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Fig. 2. Soil test P distribution for Site 3 following the 1997 growing season for the 0 and 20 kg ha–1 broadcast treatments in the no-till (NT), reduced till (RT), and plowed tillage systems for the no P (CK), broadcast P (BC), starter P, and deep P (DP) management systems.
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Probability values of tillage, P management, and tillage x management interactional effects on early season dry matter yield, P uptake, and grain yield for all crops at all locations is given in Table 3. Generally, tillage and P management did not significantly affect grain P concentration of any crop (data not shown), and will not be discussed in further detail. Treatment effects on dry matter (V6), P uptake (V6), and final grain yield will be discussed by crop.
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Table 3. Probability values for tillage (T), P management (M), and tillage x management (T x M) effects on early season dry matter production and P uptake, and grain yield for all crops at all locations.
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Corn Response
Treatment effects on early season corn growth (V6) varied. In 1997 at Sites 1 and 2, there was a significant tillage x P management interaction for both dry matter production and P uptake (Fig. 3
and 4)
. At Site 1, starter P increased DM and P uptake for the reduced till and plowed treatment, but did not significantly affect DM and P uptake for the no-till treatment. These results contradict results obtained in Iowa that showed banded P (deep or shallow) significantly increased early season dry matter production of no-till corn (Mallarino et al., 1999). This contradiction of the Iowa data might be a result of the number of years each site had been in no-till production. These Kansas sites were in the first year of no-tillage. The redistribution of P within the profile by plowing likely caused the increased response to starter P observed in the plowed treatments (Fig. 2). The early season growth differences, however, did not carry over into yield differences. In fact, there were no significant tillage, management, or tillage x management interactions for corn grain yield in 1997, at this site.
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Fig. 3. Early season dry matter and P uptake (V6) and final grain yield for corn at Site 1, 1997 for tillage: no-till (NT), reduced till (RT), and plowed (PL) and P management: check (CK), broadcast (BC), starter (ST), and deep band (DP) effects. *Grain yield reported were adjusted to a moisture level of 155 g kg–1. Error bars are the F protected LSD (p < 0.10) for the tillage x P management interaction.
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Fig. 4. Early season dry matter and P uptake (V6) and final grain yield for corn at site 2, 1997 for tillage: no-till (NT), reduced till (RT), and plowed (PL) and P management: check (CK), broadcast (BC), starter (ST), and deep band (DP) effects. Grain yield reported were adjusted to a moisture level of 155 g kg–1. Error bars and letters are F protected LSD for the interaction and main effects, respectively.
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Early season K deficiency symptoms were observed at Site 1 (1997) even though soil test K was sufficient. Potassium deficiency symptoms ranged from nonexistent in the plowed treatment to moderately severe in the no-tilled treatment. Tissue K concentration confirmed the visual symptoms. This demonstrates a need for additional research examining the tillage effects on K requirements of corn in this region of Kansas.
At Site 2, there was a significant dry matter response to broadcast and starter P for the no-till treatment, but no dry matter response to P in the reduced till or plowed treatments (Fig. 4). There was no visual K deficiency for the tillage treatment at this location, and P uptake at this growth stage was higher in the broadcast and starter treatments than in the deep placed treatment regardless of tillage practice. In 1999 at Site 2, there was not a significant tillage x P management interaction for V6 dry matter or P uptake, but tillage and P management main effects were significant. Corn in the plowed treatment accumulated significantly more dry matter and P than no-till or reduced till treatments, and P uptake at this stage was highest for the starter placement (Table 4). Higher early season growth and P accumulation seldom translated into higher grain yield.
Corn grain yield in 1997 at both sites was much higher than typically obtained in the region because of timely summer rains. Conversely in 1999, no data was collected from Site 1 due to poor emergence, and corn yield at Site 2 was substantially lower than 1997 because of poor in-season growing conditions. There was a significant tillage x placement interaction for early season dry matter and P uptake at both corn locations in 1997 (Fig. 3 and Fig. 4). The only significant effects on grain yield, however, were observed at Site 2 in 1997 (Table 3). At this site, no-till corn yield was significantly lower than reduced till or plowed planting methods, and deep P placement produced higher yields than the no P check (Fig. 4). Overall, the results show that although deep placement usually improves early season corn growth, but P management had no effect on final grain yield. Tillage impacts on corn yield were also minimal.
Grain Sorghum Response
Site 3 was in a sorghum–soybean–sorghum rotation. Early season dry matter yield, P uptake (V6), and grain yield for sorghum in both years are in Table 5. There were no tillage x P management interactions for the measured plant parameters either year, suggesting that this level of P stratification is irrelevant for grain sorghum production. Early season dry matter and P uptake for the no-till treatment were significantly higher than in the reduced till and plowed treatments in 1997, but there was no difference between tillage treatments in 1999 (Table 5). Starter P fertilizer placement produced more dry matter and maximized P uptake at the V6 growth stage in 1997, but P management did not affect the V6 dry matter or P uptake in 1999.
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Table 5. Effects of tillage and P management on dry matter (DM) and tissue P concentration at V6 growth stage and final grain yield for sorghum at Site 3 in 1997 and 1999.
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Grain yields were not affected by tillage, but were affected by P management (Table 5). Numerically, deep-banded P produced greatest grain sorghum yield in both years, but broadcast P applications in 1997 and starter P applications in 1999 were not statistically different than the deep-placed P. These results are in agreement with results obtained by Lamond (1987), showing an increase in grain sorghum yields for knifed applications of N, P, and K. Broadcast P applications in 1997 and starter P applications in 1999 were not statistically different than the deep-placed P. Deeper placed P should be considered for sorghum grown on stratified, low available P soils, but application cost may outweigh yield benefits.
Winter Wheat Response
This study contained only one site year of winter wheat, and all treatments were no-till planted into the corn residue so that planting was completed in a timely fashion. Additional research is needed to determine if results observed for this site are reproducible under different weather and soil conditions. In 1998 at the Site 2, no-till winter wheat dry matter production at the early boot stage was higher when the previous crop was plowed compared with when the previous crop no-tilled (Table 6). A study conducted by Wilhelm et al. (1989) also found that early season growth of winter wheat was slowed with increasing amounts of crop residue. Dry matter at the early boot stage was not significantly affected by P management and P uptake was not affected by either tillage or P management. Wheat grain yields were significantly lower when the previous crop was planted using no-tillage methods compared with when the previous crop was planted following moldboard plowing. Broadcast P significantly increased grain yield compared with the deep band (Table 6).
Soybean Response
Soybean was grown at Site 1 and Site 3 in 1998. Early in the season the reduced till and plowed systems had higher dry matter and P uptake compared with the no-tilled system (data not shown), but final grain yield was not significantly affected by either tillage or P management (Table 3) and averaged 1.7 Mg ha–1.
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CONCLUSIONS
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Stratification of soil test P occurs in reduced- and no-tillage systems of southeastern Kansas. This study was designed to determine the effect of tillage, and deeper placement of P fertilizer on crop growth, P uptake, and grain yield. Results show that the effects of tillage and P management on grain yield of crops grown in soil with available P (measured by soil test) stratified in the surface 15 cm were not consistent. Corn yields were only affected by tillage at one site, which occurred during the first year of no-till management. Sorghum yields were not affected by tillage, but wheat yields were significantly increased when comparing the plowed to no-till systems.
Subsurface applications of P fertilizer had a positive affect on early season crop growth and P uptake for corn and sorghum in some years. Grain yield of sorghum was generally greater with deep-banded P application, but other crops were less responsive to deep-banded P. Some crops may be more responsive to deep-placed P than others due to differences in root architectures and ability of the root to extract P from the surface few centimeters of soil. Soybean was the least responsive to P applications (of the crops in this study) whereas sorghum was the most responsive. Producers should consider both severity of P stratification in the surface layer and the intended crop to be grown when making P and tillage management decisions.
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ACKNOWLEDGMENTS
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The authors thank grower–cooperators Charles Bruner, Gale George, Bob Martin, and Mike Wilson for plot establishment, the uses of their land, and graciously agreeing to farm around research plots. Thanks also to the staff and student employees of the Kansas State Soil Testing Laboratory, especially Kathy Lowe, Gary Griffith, and Joy Pierzynski for assistance in soil and plant analysis. This research was funded by a grant from the Kansas State Fertilizer Research Fund.
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REFERENCES
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ABSTRACT
INTRODUCTION
