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Agronomy Journal 92:380-388 (2000)
© 2000 American Society of Agronomy

SOIL FERTILITY

Grain Yield, Early Growth, and Nutrient Uptake of No-Till Soybean as Affected by Phosphorus and Potassium Placement

Rogerio Borgesa and Antonio P. Mallarinoa

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

apmallar{at}iastate.edu


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
More information is needed about P and K placement for no-till soybean [Glycine max (L.) Merr.]. This study evaluated plant responses to P and K fertilization and placement in 10 long-term trials and 11 short-term trials in Iowa from 1994 to 1997. Treatments were various P and K rates broadcast, banded with the planter, and deep banded (at a 15- to 20-cm depth). Measurements were plant weight, P uptake, and K uptake at the V5 stage and grain yield. Phosphorus fertilization increased yield when soil-test P (STP) was less than 9 mg P kg-1 (Bray-P1) at a 0- to 15-cm depth or 12 mg P kg-1 at a 0- to 7.5-cm depth. The P placement did not influence yield. The band K placements produced slightly higher yield than the broadcast placement. Responses to K were not related to soil-test K (STK) levels, which varied from 90 to 262 mg K kg-1 (ammonium acetate), or stratification. The P or K placement had little influence on early growth but influenced early P and K uptake. Banding with the planter was more effective than broadcasting for P uptake, and the two band placements were more effective for K uptake. Only the responses of K uptake and grain yield to banded K were correlated across sites. A shallow sampling depth will improve only slightly the prediction of response to P. The observed small no-till soybean yield response to banded K would seldom offset increased application costs in similar soils.

Abbreviations: H, high • L, low • O, optimum • STK, soil-test K • STP, soil-test P • VH, very high • VL, very low


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
The area of no-till management in Iowa and many regions of the Midwest increased markedly during the late 1980s and early 1990s, but it has increased little since then (CTIC, 1997). Several reasons may explain this trend. One likely reason, although not necessarily the most important, is farmers' uncertainty about appropriate fertilization management for this system. No-till management usually leads to P and K stratification in soils. These nutrients accumulate in the soil surface as a result of minimal mixing of surface-applied fertilizers and crop residues with soil, limited vertical movement of P and K in most soils, and cycling of nutrients from deep soil layers to shallow layers through nutrient uptake by roots (Shear and Moschler, 1969; Griffith et al., 1977; Mackay et al., 1987; Karathanasis and Wells, 1990; Karlen et al., 1991). Phosphorus sorption and K retention by soil constituents is reduced in surface layers of no-till soils (Karathanasis and Wells, 1990; Guertal et al., 1991). A relative accumulation of P and K near the soil surface may decrease nutrient availability to plants in dry periods, however. High residue coverage in no-tilled soils usually increases soil moisture and reduces soil temperature at shallow depths, which can inhibit plant growth and nutrient availability early in the season but can increase root activity in drier periods (Barber, 1971; Al-Darby and Lowery, 1987; Fortin, 1993).

Several reports showed infrequent and small decreases in nutrient availability for crops due to nutrient stratification in high rainfall areas of the Corn Belt (Singh et al., 1966; Belcher and Ragland, 1972; Moschler and Martens, 1975). Other work (Eckert and Johnson, 1985; Yibirin et al., 1993; Lauson and Miller, 1997) showed, however, that shallow subsurface banding (5 cm beside and below the seeds) can significantly increase P and K fertilizer use efficiency compared with broadcast fertilization for no-till soybean and corn. This result coincides with long known effects of banding in minimizing retention of these nutrients by soil constituents and in increasing fertilizer use efficiency by crops.

Several studies (deMooy et al., 1973; Bharati et al., 1986; Rehm, 1986; Mallarino et al., 1991a and 1991b; Webb et al., 1992; Randall et al., 1997) showed that yield increases due to broadcast P or K fertilization of soybean in predominant Corn Belt soils are large and likely only in low-testing soils (less than approximately 16 to 20 mg P kg-1 by the Bray-P1 extractant or 90 to 130 mg K kg-1 by the ammonium acetate extractant applied to dry soil samples). Published research comparing deep-banding with other placements for no-till soybean is scarce and conflicting. Hairston et al. (1990) showed that deep injection (15-cm depth) of P and K fertilizer gave yield responses superior to broadcast placement on no-till soybean in some Mississippi soils testing low in P and K. Other research (Hudak et al., 1989) showed no K placement effect on yield of no-till soybean grown in a silt loam soil in Ohio. Recently published Iowa research for no-till corn (Bordoli and Mallarino, 1998; Mallarino et al., 1999) showed that P banding increased early growth and P uptake but did not increase yield. Deep-band K, however, did not increase early growth but increased K uptake and grain yield. Our objectives were to evaluate the grain yield, early dry weight, and nutrient uptake responses of no-till soybean to P and K fertilizer placements.


   Materials and methods
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
Results and discussion
 Conclusions
 REFERENCES
 
Sites, Trials, and Treatments
The study included long-term trials and short-term 1-yr trials. Five long-term trials for P and five for K were established in 1994 at Iowa State University research centers, which were in northeast, northern, northwest, southeast, and southwest regions. A corn–soybean rotation was established by planting both crops each year on adjacent sections of the fields. Data for soybean collected from 1994 to 1997 are reported here. Eleven short-term P–K response trials were established at farmers' fields from 1995 to 1997. The term site represents each site-year at long-term and farmers' fields trials. Soybean was always planted on corn residue. Summarized information about soil types and management practices is shown in Table 1 . Crop management practices (except P and K fertilization) were those normally used at each farm or research center. The soybean cultivars and planting dates used were among those recommended for each location. Soybean row spacing was 0.76 m at research farms and 0.19 m at farmers' fields. Plots measured 18 m in length and either 4.5 or 6.0 m in width. No field received deep-band P or K fertilization before 1994.


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  		Table 1 Location, soils, tillage history, cultivars, rainfall, and temperature for 31 sites

 
At the long-term trials, the treatments were six factorial combinations of two fertilization rates and three placements, and two nonfertilized controls. Fertilizer rates were 14 and 28 kg P ha-1 at P trials and 33 and 66 kg K ha-1 at K trials. The placements were bands applied with the planter, broadcast, and deep bands. The planter bands were approximately 25 mm in width and were placed 5 cm to the side of and 5 cm below the seeds. The broadcast fertilizer was spread by hand. The deep bands were approximately 25 mm in width and were placed 15 to 20 cm below the soil surface and spaced 0.76 m. The deep bander had a coulter-knife combination that tilled and brushed residues off a strip 12 to 18 cm in width. In one control the soil and residue were not disturbed and in the other (empty knife), plots received a coulter-knife pass of the deep bander but no fertilizer was applied. The treatments were applied for both crops each year. Thus, treatment effects on soybean measured in 1995, 1996, and 1997 likely were the result of the fresh fertilizer applications plus any residual effects from previous applications. The broadcast and deep-banded treatments were applied in spring 3 to 5 wk before planting for the 1994 and 1995 crops, and in the fall of the previous year for the 1996 and 1997 crops. Soybean on plots corresponding to the deep band treatment was planted on top of the coulter-knife tracks. A high K rate (280 kg K ha-1) was applied as one-third broadcast and two-thirds deep-banded treatments in spring 1994 at all P trials. A high P rate (120 kg P ha-1) was applied as one-third broadcast and two-thirds deep-banded treatments at all K trials. Completely randomized block designs with three replications were used for all trials. The treatment sums of squares of the measurements were partitioned into orthogonal comparisons of the two controls (absolute vs. empty knife) and of the mean of the controls vs. the mean of the fertilized treatments. The sums of squares of fertilized treatments were further partitioned into a factorial arrangement of placement, rate, and interaction effects.

At the farmers' fields, five trials were conducted in 1995, five in 1996, and three in 1997. The 14 treatments were four nonfertilized controls, the four factorial combinations of two P rates and two placements, the four factorial combinations of two K rates and two placements, and a P–K mixture applied broadcast or deep-banded. Two of the controls were absolute controls and the other two received a coulter-knife pass of the deep bander but no fertilizer was applied. The fertilization rates were 14 or 56 kg P ha-1 and 33 or 132 kg K ha-1 when P or K were applied separately. The P–K mixture treatment consisted of 56 kg P ha-1 and 132 kg K ha-1. The broadcast and deep-band placements were similar to those used at the research centers and were applied in the fall. The deep-band spacing was 0.76 m, although soybean was planted in narrow rows (0.19-m spacing). Three trials conducted in 1996 (Sites 24, 25, and 26) and two in 1997 (Sites 30 and 31) evaluated residual effects of similar treatments that had been applied for the previous year's corn crop. One 1997 trial (Site 29) evaluated residual effects of similar treatments that had been applied for the 1995 soybean crop (no P and K fertilizers were applied for the 1996 or 1997 corn or soybean crops). Completely randomized block designs with three replications were used for all trials. The treatment sums of squares were partitioned into orthogonal comparisons of the two controls (absolute vs. empty knife), the mean of all controls vs. the mean of all fertilized treatments, a P rate x placement factorial (two rates, two placements, and the interaction effects), and a similar K rate x placement factorial. To better estimate separate responses to P or K, the treatment sums of squares also were partitioned into nonorthogonal comparisons that compared the mean of all controls with the mean of plots receiving only P and the mean of all controls with the mean of plots receiving only K.

Measurements
Soil samples were collected before the treatments were first applied. Composite samples (12 cores, 2-cm diameter each) were collected randomly from two depths (0–7.5 and 7.5–15 cm). In addition, the absolute control plots of long-term trials were sampled each following year. Soil was dried at 40°C and analyzed for pH, organic C, STP, and STK using procedures recommended for soils of the North Central region (Brown, 1998). Soil pH was measured potentiometrically using a 1:1 soil:water ratio, organic C with the Walkley-Black method, STP with the Bray-P1 extractant, and STK with the ammonium acetate extractant. Results for pH and organic C (0–15 cm depth) are shown in Table 1; results for STP and STK (for various depths) are shown in Table 2 . We used Iowa State University soil-test interpretations for samples collected from 0- to 15-cm depth and low subsoil P and K. Boundaries for the STP classes very low (VL), low (L), optimum (O), high (H), and very high (VH) are 0 <= VL <= 8, 8 < L <= 16, 16 < O <= 20, 20 < H <= 30, and VH > 30 mg P kg-1. Similar boundaries for STK are 0 <= VL <= 60, 60 < L <= 90, 90 < O <= 130, 130 < H <= 170, and VH > 170 mg K kg-1.


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  		Table 2 Soil-test P and K values for all sites.{dagger}

 
The aerial parts of 10 soybean plants were sampled at the V5 growth stage (Fehr et al., 1971) by cutting plants at ground level. All plots were sampled with the exception of the empty coulter-knife control at the long-term trials. No samples were collected from Site 21. Plant samples were dried in an air-forced oven at 60°C and weighed. Total P and K was measured by digesting 0.25 g of material with sulfuric acid and hydrogen peroxide (Digesdahl Analysis System, Hatch, Boulder, CO). The P in the digests was measured by colorimetry (Murphy and Riley, 1962) and K was measured by flame emission. Total plant P or K uptake was calculated from the P or K concentration and dry weights. The tissue P and K concentrations are not shown, but they can be calculated from the data presented.

At the long-term sites, grain was harvested from a central area of each plot (15-m length of three or five rows) with a plot combine. At the farmers' fields, plants from a central plot area measuring 7.6 or 9.1 m in length or 1.1 to 1.5 m in width (depending on the year) were cut and threshed using a stationary thresher. Yields were corrected to 130 g kg-1 moisture. Daily rainfall was measured at some sites (Sites 1–8 and 13–20) or were obtained from the nearest (3–25 km) weather station for other sites.


   Results and discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
Conclusions
 REFERENCES
 
Study of yield responses showed that P and K increased soybean yields at several sites, but there were no significant differences (P <= 0.1) between the two P or K fertilization rates and no significant interactions between fertilization rates and placements for either nutrient at any site. Furthermore, comparisons of yields with a P–K mixture and with similar but separate P or K rates at the short-term trials indicated no significant P x K interaction at any site. Because of these results, only the means of the two fertilization rates for each nutrient are reported. Also, the means of the absolute control and coulter-knife control are shown because these treatments did not influence early growth or grain yield at any site.

Grain Yield Response to Phosphorus Fertilization and Placement
At long-term trials (Table 3) , P fertilization increased yield (P <= 0.1) at seven sites (Sites 5, 7, 8, 9, 10, 11, and 12). The statistical analysis would suggest that P also influenced yield at Site 3, but this is not the most appropriate conclusion. The yield of the control was intermediate between the broadcast and band placements, and nonorthogonal comparisons showed no difference between each fertilized mean and the control. The responsive sites had less than 9 mg P kg-1 at a 0- to 15-cm depth or 12 mg P kg-1 at a 0- to 7.5-cm depth, although responses did not occur in all low-testing soils. At Site 9, the broadcast placement was better than the band placements. At Site 11, the two band placements produced the highest yields. The positive response to P banding at this site (same location as Site 9, but 2 yr later) could be attributed to a combination of very low STP and little rainfall recorded in May 1996. Although other sites had low or very low STP and received little rain early in the season, Site 11 presents one of the worst combinations of STP and rainfall. An analysis across all long-term sites showed a significant response to P fertilization but not to P placement. The interaction rates x site was significant (P <= 0.1, not shown), which confirms the different responses observed at some sites.


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  		Table 3 Yield of soybean as affected by P fertilization and placement

 
At the short-term trials (Table 3), statistical analyses by site show P placement differences only at Sites 26 and 28. These responses are difficult to interpret. Both sites high in STP, the yield of the control was intermediate between the yields of the deep-band and broadcast placements, but nonorthogonal comparisons showed that neither fertilized mean differed from the control. Analyses of variance by site showed no significant response at other sites, although most tested low. An analysis across all sites showed a small positive effect of P fertilization and no placement difference. This small but significant response across sites could be explained by small responsive trends at various sites.

The lack of grain yield response at sites with STP optimum or above coincides with published results (Mallarino et al., 1991a; Webb et al., 1992) for soybean managed with chisel-plow tillage and broadcast P. The previous research showed an almost nil probability of response in the optimum interpretation class (less than 16 mg P kg-1, 0–15 cm depth) or higher classes. The lack of large yield responses at several low-testing soils (0–15 cm sampling depth) in this study raises questions about the applicability of soil-test P interpretations from chisel-plow to no-till soybean. Contrasting results for no-till corn were reported by Bordoli and Mallarino (1998) because corn responded to P in most low-testing soils, and the sampling depth did not influence the prediction of responses. We postulate two possible reasons for the lack of soybean response to P at several low-testing soils. One is that no-till soybean may require a different STP calibration from that of tilled soybean or no-till corn. In average, soils had 65% more STP in the 0- to 7.5-cm depth than in the 7.5- to 15-cm depth (Table 2) and the range across sites was 8 to 283%. This cannot be proved conclusively with our data because the correlation between relative yield response to P (which can be calculated from the data presented in Table 3) across sites and STP was only slightly better for the 0- to 7.5-cm depth (r = -0.46, P <= 0.01) than for the 0- to 15-cm depth (r = -0.41, P <= 0.02). Also, use of the shallow depth and current soil test interpretations would have improved little the prediction of responsive and unresponsive sites. When a 0- to 15-cm depth was used, 16 sites tested less than 16 mg P kg-1 (below optimum), seven sites were responsive, and nine sites were unresponsive. When a 0- to 7.5-cm depth was used, only 15 sites tested below optimum, the same seven sites were responsive, but only eight were unresponsive.

The second possible explanation relates to rainfall in late spring and early summer and to soybean growth patterns. Rainfall during June and July was frequent and high (and probably excessive) in many locations (Table 1), and grain yield across sites was negatively correlated (P <= 0.1) with rainfall in each of those months. The high amount and frequency of rainfall may have allowed for higher root activity near the soil surface and may partly explain the small or lack of yield response to P at several low-testing sites. This effect could have been even more probable at the farmers' fields because they had longer no-till histories and soybean was planted in narrow rows. It is possible that a more uniform distribution of plants (and roots) and prolonged no-till management results in a more efficient utilization of P from shallow soil layers.

Grain Yield Response to Potassium Fertilization and Placement
In long-term trials, K fertilization increased (P <= 0.1) grain yields at five sites and the K placements differed at only two sites (Table 4) . At Site 7 the two band placements produced statistically similar yields, which were higher than for the broadcast placement. At Site 4, only the broadcast placement increased yield. An analysis across all long-term sites showed a higher yield response to deep-band K. At short-term trials, analyses by site showed that K fertilization influenced yields significantly only at Sites 21 and 31. At Site 21, the two placements did not differ. At Site 31, the yield of the control was intermediate between the broadcast and deep-band placements, which is difficult to interpret. A yield reduction by the deep K placement seems unlikely because this site evaluated the residual effect of treatments applied for the previous corn crop. An analysis across all short-term trials showed a small, significant response to K fertilization but not to placement, although the mean for the deep-band placement was the highest. The small additional soybean response to deep-band K observed in this study is in contrast with responses of no-till corn reported by Bordoli and Mallarino (1998) for similar soils. No-till corn showed a more frequent and large yield response to deep-band K, and in corn the planter-band and broadcast K placements did not differ.


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  		Table 4 Yield of soybean as affected by K fertilization and placement

 
The yield response to K fertilization or placement across sites was not correlated with STK at any depth. The STK stratification in these soils was less than for P; on average the soils had 37% higher STK in the 0- to 7.5-cm depth than in the 7.5- to 15-cm depth, and the range was 1 to 108%. All soils had STK levels (0–15 cm depth) optimum or higher according to current interpretations. Our results cannot be directly compared with previous Iowa research (Mallarino et al., 1991a and 1991b) for tilled soybean and broadcast K because those studies applied the ammonium acetate K test to field-moist samples. This test extracts less K from field-moist soil than from air- or oven-dried soil (Luebs et al., 1956). The yield response to K placement was not related to deficient rainfall during spring or summer, as was shown for no-till corn by Bordoli and Mallarino (1998). The lack of a statistical K placement difference in the short-term trials is in contrast with the advantage for the deep-band placement observed in the long-term trials. This difference could be related to the fact that soybean was planted in wide rows in the long-term trials and in narrow rows at the short-term trials. When a wide row spacing was used, the rows were placed on top of the knife tracks and plants along a row were closer to each other. Analyses of plants from deep-band and inter-band areas of Sites 22, 23, 27, and 28 (not shown) at the V5 growth stage showed that K uptake was 20% higher in the deep-band areas.

Early Growth Response to Fertilization and Placement
At long-term trials, P fertilization increased (P <= 0.1) early growth at Sites 11 and 16 (Table 5) . At Site 11, only the two band placements increased growth. At Site 16, all placements increased plant dry weight, and the increase was higher for the two band placements. An analysis across all long-term sites shows a significant response to P fertilizer and a lack of placement effects, although means for both band placements were higher. At short-term trials, P fertilization increased early growth at two sites. At Site 25, the broadcast placement increased yields more than the deep placement did. At Site 27, the two placements did not differ. The statistical analysis across all short-term trials confirms a response of early growth to P, which was higher for deep placement (P <= 0.08). Small and frequent responses to the P undetected by the analyses of variance by site explain the overall response.


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  		Table 5 Early growth of soybean as affected by P fertilization and placement

 
Potassium fertilization increased soybean early growth at five long-term sites (Sites 3, 8, 9, 10, and 14) (Table 6) . All placements decreased early growth at Site 1, a result that cannot be explained because even the low rate decreased growth (not shown). Among the sites with positive responses, the placements differed only at Site 3 and 8, where the two band placements increased yield over the control. An overall analysis of variance detected no response across sites, probably due to the negative response in Site 1. An analysis without Site 1 revealed a positive response to fertilization and to both band placements (P <= 0.1, not shown). At the short-term trials, K fertilization increased early growth only at Site 25, but small, nonsignificant effects at other sites probably explain a small significant response to K across all trials. The placements did not differ at any site or across all sites.


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  		Table 6 Early growth of soybean as affected by K fertilization and placement

 
The responses of early growth and grain yield were not related. Only one P site (Site 11) and one K site (Site 10) showed responses of both early growth and grain yield to fertilization. Moreover, the correlation across sites between relative yield and early growth responses was not significant (P <= 0.1) for either nutrient or placement. Thus, increased early growth was of no benefit for yield production in these sites. Environmental growing conditions later in the season may have precluded any influence of increased early growth on grain yield. A lack of relationship between increased early growth (mostly due to P banding) and grain yield was also observed for no-till corn in Iowa (Mallarino et al., 1999).

Effects of Fertilizer Placement on Early Plant Nutrient Uptake
Phosphorus fertilization increased (P <= 0.1) P uptake at six long-term sites (Table 7) . The placements did not differ at Sites 8 and 12, the two band placements increased P uptake more than the broadcast placement at Sites 10 and 11, and only the planter-band P increased P uptake at Sites 13 and 16. An analysis across all sites revealed a significant response to P fertilization and to the planter-band placement. At the short-term trials, P fertilization influenced soybean P uptake at five sites. The placements did not differ at Sites 22, 24, and 27, and the deep placement was better at Site 25. A statistically significant placement effect at Site 30 is difficult to explain because the control is intermediate between the broadcast and deep-band placements. In contrast to results for yield and early growth, the high P rate increased P uptake over the low rate at three sites (not shown). Although P uptake was not increased at all sites, the influence of P fertilization and placement on early P uptake was more frequent and more marked than on grain yield or early growth. Correlations between relative increases in yield, early growth, and P uptake across sites were not significant (P <= 0.1).


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  		Table 7 Early P uptake by soybean as affected by P fertilization and placement

 
Potassium fertilization and placement influenced early plant K uptake frequently. At the long-term trials (Table 8) , K fertilization increased K uptake at 10 sites, and the placements differed at seven sites. The band placements were statistically similar and better than the broadcast placement at six sites (Sites 3, 7, 8, 10, 12, and 13), whereas the deep-band placement was the best at Site 15. An analysis across all long-term sites showed that only the two band placements increase K uptake. At the short-term trials, K fertilization increased K uptake at six sites and the placements differed only at Site 26, where the deep band was better. An analysis across all short-term trials shows a significant response to K fertilization but no placement difference. In contrast with results for grain yield and early growth, the high K rate increased K uptake over the low rate at five sites and in the analysis across all long-term sites (not shown). The K fertilization and placement influence on K uptake was not obviously related to STK or stratification, which is consistent with luxury uptake of K. The deep-band K had small effects on plant growth but increased K uptake markedly. The frequent and marked response of K uptake to the banded K was in agreement with small (although often not confirmed by statistical analyses by site) yield response to banded K. Moreover, the correlation across sites between relative increases in yield and K uptake due to banded fertilization was positive and significant (r = 0.46, P <= 0.01).


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  		Table 8 Early K uptake by soybean as affected by K fertilization and placement

 
Although we found no advantage for deep banding of P, its potential benefit in reducing P contamination of surface water supplies should be considered. As expected, analyses of soil samples collected after the last harvest showed that only the deep-band placement reduced STP stratification markedly. The mean STP in the 0- to 7.5-cm soil layer for the 28-kg rate across all long-term trials was similar for the broadcast and planter-band placements (42 mg P kg-1 for the broadcast and 43 mg P kg-1 for the planter-band) and was higher (P <= 0.05) than for the deep-band placement (28 mg P kg-1). When compared with STP in the 7.5- to 15-cm soil layer, these concentrations were 207% higher for the broadcast placement, 112% higher for the planter-band placement, and not different (only 4% higher) for the deep-band placement. Thus, the deep placement markedly reduced P accumulation near the soil surface, which is likely to reduce soluble P losses with water runoff.


   Conclusions
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
REFERENCES
 
Phosphorus fertilization increased yield only in several low-testing soils. There was no large or consistent yield or early growth response to P placement, although both band placements increased plant P uptake more than the broadcast placement did. Measuring soil P in the shallower layer sampled (0–7.5 cm) improved only slightly the prediction of responsive and unresponsive soils compared with a 0- to 15-cm sampling depth. Soybean showed small yield responses to K fertilization in several sites, even though soil K was optimum or higher according to current interpretations for tilled soils. The yield response to K was not correlated with the soil K level or stratification. The two band K placements often produced slightly higher yields than the broadcast placement, and increased K uptake markedly. The slightly higher response of soybean to the deep-band K placement observed in this study together with previously reported larger responses of no-till corn to deep-band K suggests that this placement is the most efficient for corn–soybean rotations managed with no-tillage.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
Iowa Agric. Home Econ. Exp. Stn. Journal Paper No. J-18314. Project 3233. This work was supported in part by the Iowa Soybean Promotion Board.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 




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Response of Soybean Grain Oil and Protein Concentrations to Foliar and Soil Fertilization
Agron. J., May 13, 2005; 97(3): 910 - 918.
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J. W. Singer, K. A. Kohler, M. Liebman, T. L. Richard, C. A. Cambardella, and D. D. Buhler
Tillage and Compost Affect Yield of Corn, Soybean, and Wheat and Soil Fertility
Agron. J., March 1, 2004; 96(2): 531 - 537.
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G. W. Rehm and J. A. Lamb
Impact of Banded Potassium on Crop Yield and Soil Potassium in Ridge-Till Planting
Soil Sci. Soc. Am. J., March 1, 2004; 68(2): 629 - 636.
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D. J. Wittry and A. P. Mallarino
Comparison of Uniform- and Variable-Rate Phosphorus Fertilization for Corn-Soybean Rotations
Agron. J., January 1, 2004; 96(1): 26 - 33.
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R. Borges and A. P. Mallarino
Broadcast and Deep-Band Placement of Phosphorus and Potassium for Soybean Managed with Ridge Tillage
Soil Sci. Soc. Am. J., November 1, 2003; 67(6): 1920 - 1927.
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X. Yin and T. J. Vyn
Potassium Placement Effects on Yield and Seed Composition of No-Till Soybean Seeded in Alternate Row Widths
Agron. J., January 1, 2003; 95(1): 126 - 132.
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X. Yin and T. J. Vyn
Soybean Responses to Potassium Placement and Tillage Alternatives following No-Till
Agron. J., November 1, 2002; 94(6): 1367 - 1374.
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X. Yin and T. J. Vyn
Residual Effects of Potassium Placement and Tillage Systems for Corn on Subsequent No-Till Soybean
Agron. J., September 1, 2002; 94(5): 1112 - 1119.
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The SCI Journals Crop Science Vadose Zone Journal
Journal of Natural Resources
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Environmental Quality		 The Plant Genome