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SOIL FERTILITY

No-Tillage Soybean Response to Banded and Broadcast and Direct and Residual Fertilizer Phosphorus and Potassium Applications

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011 USA

tpolito{at}iastate.edu

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 
Improved P and K management systems for no-tillage soybean [Glycine max (L.) Merr.] may be needed to increase yield and profits. This study evaluated the response of soybean to fertilizer P or K rates and placement as well as residual and direct fertilization from 1995 through 1996. Two K and two P experiments were established on farmers' fields with 10-yr histories of no tillage. An additional P experiment was conducted on one of Iowa State University's research farms. Treatments on farmers' fields included two rates of P (0 and 19.5 kg P ha^-1) or K (0 and 51 kg K ha^-1), placement of fertilizer (surface broadcast or a subsurface band 5 cm beside and 5 cm below the seed ) and time of fertilizer application. Treatments on the research farm were similar, except the P fertilizer rates applied were 0, 19, 39, and 78 kg ha^-1. Leaf P and K concentrations and grain yields were measured. Soil test P and K levels at the 0- to 15-cm depths ranged from low to very high across sites at the beginning of the experiment. Placement effects were variable for leaf P or K concentrations. Grain yields for broadcast P and K were as good as or better than the banded applications. However, there may be an advantage to applying P directly to the soybean crop, at least when soil test levels are optimum or lower.

Abbreviations: CR, Cedar Rapids • MK, Maquoketa • NM, New Market • NWRC, Northwest Research Center • STK, soil test K • STP, soil test P • WB, Webb

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 
NO-TILLAGE CROP PRODUCTION has been recommended as a cost-effective way of reducing soil erosion (Amemiya, 1977; Unger and McCalla, 1980). However, soils under no-tillage systems are usually cooler, wetter, and less aerated than those under conventional tillage systems. Such conditions may influence plant nutrient absorption by slowing root growth and reducing the release of N, S, and P from soil organic matter.

Surface application of P and K fertilizer and limited incorporation of crop residue into the soil in no-tillage systems lead to stratification of P and K in the upper root zone (Ketcheson, 1980; Shear and Moschler, 1969). Placement of P and K in soil zones that are susceptible to drying may limit soybean uptake of these nutrients in no-tillage systems during periods of low rainfall. This is because P and K diffusion rates decrease as soil water content decreases. Limited P and K uptake reduces soybean shoot growth and utilization of applied P and K (Kaspar et al., 1989).

Residual effects from large P applications were observed on high P-fixing soils, in which adequate P was supplied for corn 7 to 9 yr after application (Kamprath, 1967). Corn (Zea mays L.) has been found to be significantly more responsive than soybean to direct and residual fertilizer P and to direct application of K (deMooy et al., 1973).

Ham and Caldwell (1978) reported that fertilizer P increased soybean production but placement had no significant effect on yield and P uptake. The Ham and Caldwell (1978) paper did not report the tillage system used in their study, but two other papers did. Those papers reported no yield increases from different P and K fertilizer placement methods under conventional-tillage systems when soil test levels were high (Ham et al., 1973; Rehm et al., 1988). However, at low soil test P levels, the largest response was from broadcast fertilizer. Early research in Iowa indicated banding of fertilizers was equal or superior to broadcasting fertilizers if contact with the seed was avoided (Coe, 1926). Prummel (1957) found banded K fertilizer in cereals was 3.65 times more effective than broadcast, which he attributed to reduced K fixation. Furthermore, Bullen et al. (1983) reported that soybean yield increases from P applied in a band near the seed were superior to those resulting from broadcast applications. In contrast, Lutz and Jones (1974) have shown that broadcast application of P would improve soybean yields when compared with deep placement.

Fertilizer management may need to be modified to ensure that no-tillage soybean yields are not limited by P and K stratification or other changes in the soil environment. Less attention has been devoted to the evaluation of the effect of P or K placement as well as direct and residual P and K fertilization on no-tillage soybean production when soybean is grown in rotation. Our objectives were to evaluate the effects of surface broadcast and subsurface (banded at planting) placement of P or K fertilizers as well as the direct and residual responses of no-tillage soybean to P or K when grown in rotation with corn in a dryland environment.

	Materials and methods

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 
Field experiments were conducted in 1995 and 1996 on four private farms where no-tillage practices had been in place for at least 10 yr. The experiments studied the effects of banded or broadcast fertilizer P or K placement and direct or residual time of application on leaf P or K concentrations and grain yield of no-tillage soybean in Iowa. Phosphorus experiments were established near Cedar Rapids (CR) and New Market (NM), and K experiments were located near Maquoketa (MK) and Webb (WB). An additional P experiment was established at Iowa State University's Northwest Research Center (NWRC) near Sutherland. A corn–soybean rotation was established at each site by alternating the two crops between adjacent fields each year (this report is limited to data on soybean). Corn preceded soybean each year. Experiment sites, planting dates, soybean cultivars, and respective soil types are listed in Table 1 . The cultivars used were those recommended by the cooperator at each site.

The experimental design for each experiment was a randomized complete block with four replications. There were eight treatments at each P and K site on farmers' fields, with the treatments being factorial combinations of two fertilizer rates, two application times (annual and semiannual), and two placement methods. The fertilizer rates that follow are reported as the total amount applied in the 2-yr rotation. At the P sites, the rates were 0 and 39 kg P ha^-1 (triple superphosphate). At the K sites, the rates were 0 and 102 kg K ha^-1 (KCl). The application times included a direct treatment where half of the 2-yr rate was applied each year, half to corn and half to soybean, and a residual treatment where the entire 2-yr amount was applied to corn and nothing was applied to following year's soybean. The 1994 cropping year was a setup year for the residual treatments on farmers' fields. Appropriate fertilizer applications, either direct or residual treatments, were applied as outlined in Table 2 . The responses to direct (annual) applications of 19.5 kg P ha^-1 and 51 kg K ha^-1 and residual (semiannual) effects of 39 kg P ha^-1 and 102 kg K ha^-1 were measured on soybean in 1995 and 1996.

The experiment at the NWRC also included adjacent areas that were rotated between corn and soybeans. The treatments were factorial combinations of four P rates (0, 19, 39, and 78 kg ha^-1), two placement methods (broadcast and band), two timings of fertilizer application (direct and residual), and two row spacings (25- and 75-cm rows). This experiment was initiated in 1992, so treatment effects were measured in 1994 through 1996. As in the experiments on private farms, the P rates reported above for NWRC are the total applied in the 2-yr rotation. For example, the 19 kg ha^-1 direct rate consisted of 9.5 kg ha^-1 applied in each of 2 yr, whereas the 19 kg ha^-1 residual rate consisted of 19 kg ha^-1 applied only to the previous year's corn, with the treatment results measured in the following year's soybean crop.

Placement methods were surface broadcast applications and banded applications approximately 10 cm deep prior to planting. The broadcast fertilizer was spread uniformly over the soil surface and was incorporated only to the extent that the planter incorporated it.

Plot size varied slightly among sites. Plot width on farmers' fields was 3.0 m (four soybean rows spaced 75 cm apart). Plot width at NWRC was 6.0 m (eight soybean rows spaced 75 cm apart or 24 rows spaced 25 cm apart). Plot length varied from 14 to 17 m.

Composite soil samples were collected randomly from each plot of all the P and K experiments at all experimental sites before any fertilizer applications. Cores (2.5-cm diam.) were taken to a depth of 15 cm and divided into three depths (0–5, 5–10, and 10–15 cm), air-dried, ground, and passed through a 2-mm sieve before analyses. Soil test available P (STP) was determined by the Bray-1 method at all sites except WB, where the Olsen method was used. Exchangeable soil test K (STK) was determined by the ammonium acetate method. Soil test values were determined by standard soil testing procedures used in the North Central Region (North Dakota Agric. Exp. Stn., 1988).

In this study, Iowa State University soil test interpretations (Voss et al., 1996) for samples collected from the 0- to15-cm depth are used. Boundaries for the STP classes very low, low, optimum, high, and very high are 8, 16, 20, 30, and >30 mg kg^-1, respectively. Similar boundaries for STK are 60, 90, 130, 170, and >170 mg kg^-1, respectively.

Leaf samples consisting of the most recently developed, fully expanded trifoliate leaf (petiole excluded) were collected at early bloom and analyzed for P or K. Procedures used for the determination of plant P and K concentrations consisted of oven drying at 60°C, grinding, and digesting the leaves in concentrated sulfuric acid and hydrogen peroxide in a Digesdahl Analysis System (Hach, Boulder, CO; Hach Co., 1991). Leaf tissues were ground in a Wiley mill (Arthur K. Thomas Co., Philadelphia) to pass a 2-mm screen. Phosphorus was measured by colorimetry (Murphy and Riley, 1962), and K was measured by flame photometry.

After soybean reached physiological maturity, grain yield was determined by harvesting the center two rows of each plot at each farmer's field with a plot combine. An area of 42 m² was harvested at NWRC for each plot each year. Grain yield was adjusted to a moisture content of 130 g kg^-1.

Data were analyzed separately for each site-year by analysis of variance procedures because different cultivars were planted each year. Mean separation was accomplished using Fisher's protected or orthogonal contrasts, where appropriate. The treatment sums of squares were partitioned into orthogonal comparisons of the controls (B0 vs. S0), the mean of the controls vs. the mean of all fertilized treatments, and the mean of direct application vs. the mean of residual application.

	Results

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 
Precipitation for the growing period (May to September) was below average at the NM and MK sites in 1995, despite above-average rainfall in May and June. In 1996, precipitation was above average at all sites.

Farmers' Fields
At the beginning of the study, the surface 5-cm soil layer of the host farms had higher soil P and K values than the subsurface (5- to 15-cm) depths (Table 3) . The initial soil P and K levels of the farmers' fields in the surface 15-cm soil depth ranged from optimum to very high across sites (Voss et al., 1996). In 1996, the mean of the control treatments at the NM site had dropped to low in STP (13 mg kg^-1). At the other sites, soil P and K levels in the surface 15-cm soil depth were still within the optimum or higher ranges by the third year of the study, even though the levels decreased in the unfertilized plots with time.

Research Farm Experiment
Average soil P and K levels of the NWRC site in the surface 15-cm soil depth in 1994 were 19 and 202 mg kg^-1, respectively. Such P and K levels are considered to be optimum and very high, respectively. The control plots averaged 14 mg kg^-1 (low), which is below the experiment average. By 1996, the average soil P level of the control plots had dropped to very low (6 mg kg^-1), but the K level was high (170 mg kg^-1).

Leaf Phosphorus Concentrations
Leaf P concentrations (Table 6) ranged from 2.4 to 4.3 g kg^-1 over the three years. Table 6 shows significant main effect differences in 1994 and 1995. However, since all the treatments were involved in significant interactions, the interactions will be described for those two years only. In 1994, significant P rate x time of fertilization x row spacing interactions were observed for leaf P concentration. The 19 and 39 kg P ha^-1 direct rates increased P concentration in the 25-cm rows (33 and 38% more), as opposed to equivalent treatments in the 75-cm rows. Additionally, the 19 and 39 kg P ha^-1 direct rates increased leaf P concentrations by 18 and 23%, respectively, in 25-cm rows when compared with residual effects of equivalent rates.

There were no significant interactions for leaf P concentrations in 1996. The 78 kg P ha^-1 rate raised leaf P concentrations significantly when compared with the 0 and 19 kg P ha^-1 treatments. In addition, the 75-cm row spacing had significantly higher leaf P concentrations than the 25-cm spacing.

Grain Yield
There were no significant interactions among the various factors for grain yield. The response to direct application of P was 0.2 and 0.1 Mg ha^-1 larger than the response to residual applications in 1994 and 1996, respectively (Table 7) . Banded P application was not better than broadcast application at NWRC. When averaged over all other treatments, soybean yield increases occurred from P applications in 1994 and 1996. The application of the 19 kg P ha^-1 raised grain yield by 0.2 Mg ha^-1 in 1994. In 1996, the 39 kg P ha^-1 also resulted in a 0.2 Mg ha^-1 increase as compared with the control plots. Row spacing had a significant effect on grain yield in 1994 and 1996. On average, the 25-cm rows gave 0.4 and 0.2 Mg ha^-1 yield advantages over the 75-cm rows in 1994 and 1996, respectively. However, the lack of significant interactions involving row spacing indicated that the impact of fertilizer placement and the impact of direct or residual applications are the same regardless of row spacing.

	Discussion

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

Small and Ohlrogge (1973) determined that plant sufficiency ranges for P and K were 2.6 to 5.0 and 17.1 to 25.0 g kg^-1, respectively. Thus, at early bloom, leaf P and K concentrations in this study were mostly within the sufficiency range, although K concentrations of the control plots at the WB site in 1996 were generally below the listed sufficiency range.

Fertilizer placement on farmers' fields did not affect the concentration of the fertilizer nutrient in the leaf at early bloom. Banding and direct application of increasing P rates generally increased leaf P concentrations at NWRC. Increases in K concentrations occurred with K fertilization only in two site-years (MK-1995 and WB-1996).

Soybean yields for the control treatments were not significantly different from those of the fertilized treatments in 9 of 11 site-years. On farmers' fields, little or no response to added P and K fertilizers occurred when the soil test levels were optimum or higher.

The results suggest that the P and K levels on farmers' fields, although stratified, were sufficient to meet the nutritional requirements of soybean. The lack of significant positive grain yield responses to P and K fertilization may be attributed in part to the high levels of P and K availability at the nonresponsive sites. A similar lack of response to P or K on soils with high P and K fertility has been reported (Bharati et al., 1986; Mallarino et al., 1991; Rehm, 1986). Added P fertilizer increased soybean yields in two of seven site-years on soils with low and very low STP. These responses were expected, because most studies indicate that soybean responds well to P fertilizer when the soil is low in P. The results validate the categories of soil P and K availability presently used for making P and K fertilizer recommendations for no-tillage systems in Iowa.

Soybean responded to P fertilizer in the year of application more frequently than to residual P fertilizer applications. These observations indicate that application of a given quantity of P in smaller annual P applications may be more effective than larger semiannual applications for increasing soybean yields, especially when soil test levels are below optimum. Residual and direct K fertilization resulted in similar grain yields at both K sites. This corroborates the work of deMooy et al. (1973) in conventional tillage.

The results obtained from the P sites did not agree with those of Bullen et al. (1983), who concluded that soybean yield increases were higher with banded fertilizer P when compared with broadcast applications. Broadcast K increased yields in only one of four site-years in these studies. No yield response to banded P or K fertilizers occurred in any site-year. Therefore, it is evident from these studies that surface-broadcast P or K fertilizers are equal or superior to subsurface band placement in no-tillage soybean production systems in Iowa. This equal response holds true whether soybeans are planted in 25- or 75-cm rows.

	Conclusions

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 
Results of this study suggest that soybean yield responses to added P and K were seldom observed when STP and STK values were optimum or above. While the stratification of P and K levels was consistent, it did not seem to influence soybean yields on these soils that tested predominantly optimum or higher. Soybean responded to broadcast P or K applications as well as or better than to band applications, despite the stratification of nutrients. Thus, there is probably no yield advantage in banding P or K for no-tillage soybean when soil tests are in the optimum, high, or very high ranges.

Because the response to residual and direct fertilizers was negligible for soybean grown on high-testing soils, P and K fertilizer application to corn in a 2-yr cropping sequence on such soils seems to be adequate. However, direct fertilizer applications in the year soybean was grown proved beneficial on soils testing low and very low in these experiments. Recommended soil test P and K interpretations for soybean based on conventional tillage also may be appropriate for these no-tillage systems. Furthermore, P and K stratification and placement methods for these nutrients may not be major issues for no-tillage soybean production in Iowa.Hach 1991; Hall 1905

	NOTES

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 
Journal Paper no. J-18375 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA, Project no. 3066, and supported by the Hatch Act and the State of Iowa.

¹ Mention of trade or commercial names is made for information only and does not imply an endorsement, recommendation, or exclusion by Iowa State University.

Received for publication May 3, 1999.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 

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• Hach Co. Instructional manual, Digesdahl digestion apparatus model 23130-20. Boulder, CO: Hach Co, 1991.
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