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DIVISION S-8—NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Impact of Banded Potassium on Crop Yield and Soil Potassium in Ridge-Till Planting

Dep. of Soil, Water, and Climate, 1991 Upper Buford Circle, Univ. of Minnesota, St. Paul, MN 55108

^* Corresponding author (rehmx001{at}umn.edu).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Adequate application of fertilizer K has been identified as a key management practice needed to achieve optimum production in a ridge-till planting system. However, the impact of K fertilization frequency has not been documented. Additionally, banded application of K also raises questions about the correct procedure to be followed for collection of soil samples. This study was conducted in the fields of three farmers who used the ridge-till planting system for corn (Zea mays L.) and soybean (Glycine max L.) grown in rotation. Potassium was applied in a subsurface band in the center of existing ridges in the fall of Year 1 before corn and Year 2 before soybean at rates of 0, 18.5, 37.0, 55.5, and 74.0 kg ha^–1. To measure the effect of residual K on soybean yield, the rates were doubled and applied only once (before Year 1). Grain yield of both corn and soybean at all sites was not affected by K application. Potassium uptake by young corn plants was increased by K rate, but uptake was not related to yield. Potassium use had no significant effect on K concentration in the most recently matured soybean trifoliate leaves sampled at early bloom. At two sites, banded K produced changes in soil test K to a depth of 15.0 cm at a distance to 15.0 cm from the row.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
WITH ADEQUATE SOIL moisture, K availability has been demonstrated to be beneficial for both corn and soybean production (Heckman and Kamprath, 1992; 1995). With no-till planting, fertilizer placement options for optimum K uptake are frequently restricted by the lack of soil disturbance. Therefore, response to subsurface placement of K is often greater for this tillage system compared with systems using full width tillage (Eckert and Johnson, 1985; Yibirin et al., 1993).

Application of K in a subsurface band has often been proven to be effective for increasing corn yields in no-till planting systems. Howard and Tyler (1987) reported that application of K in a subsurface band in a no-till system increased corn yields while broadcast applications had no effect on production. Bordoli and Mallarino (1998), working with no-till planting systems, reported that high rates of either broadcast or planter-banded K did not offset the effect of K in a band placed at a depth of 10 to 15 cm.

Ebelhar and Varsa (2000) working with no-till planted corn measured a positive response to K applied in a subsurface band when soil test K (0–15 cm) ranged from high to very high (210–290 mg kg^–1). Positive responses to the application of K in a subsurface band were also reported by Buah et al. (2000). In those trials, soil test K (1 M ammonium acetate extract) in a no-till planting system ranged from 106 (optimum) to 274 (very high) mg kg^–1.

The ridge-till planting system can also be used to reduce soil erosion. In contrast to no-till, crops are grown on a small broad ridge formed when corn is cultivated. Unless weed growth is a serious problem, the soybean crop is not cultivated. A positive response to the application of K in a subsurface band in this planting system has been documented by Rehm (1995). In that study, the K was applied in a band at a depth of 10 to 15 cm. This positive effect was observed when the soil test for K (0–15 cm) was defined as high (140 mg kg^–1; Rehm et al., 2001). Further documentation of the response of corn grown in a ridge-till planting system to application of K in a subsurface band, however, is limited.

These prior studies utilizing the no-till and ridge-till planting systems lead to the conclusion that application of K in a subsurface band is necessary for optimum corn yields. The necessity for this placement of fertilizer K may not be appropriate for all fields. Using a measure of K extracted by 1 M ammonium acetate, it should be possible to distinguish responsive from nonresponsive situations. A definition of soil test K values that might be classified as low (response to K fertilization expected) or high (no response expected) has not yet been developed.

Application of fertilizer K for soybean in conservation tillage production has not been fully evaluated. Hudak et al. (1989) placed K fertilizers in bands that covered 12 to 100% of the soil surface and reported highest soybean yields where K was concentrated in the smallest area. Working with soybeans in a no-till system, Borges and Mallarino (2000) reported that responses to K were not necessarily related to soil test K, which varied from 90 to 262 mg kg^–1 (medium to very high). Also working with no-till soybeans, Buah et al. (2000) concluded that soybean yield response to added P and K was seldom observed when soil test K values were optimum and high (106–274 mg kg^–1).

In the northern and western Corn Belt, crop producers prefer to apply immobile nutrients before the corn crop in the corn–soybean rotation. Frequently, the residual nutrients have a positive effect on yield. While residual effects of K fertilization have been documented where full width tillage is used, the residual effect of K applied in a subsurface band in either no-till or ridge-till systems has not been widely researched. Buah et al. (2000) evaluated the residual effect of four placements of K and concluded that response to K was negligible for situations when soil test K was high (>120 mg kg^–1). There was clearly a need for further quantification of the residual effect of K applied in a subsurface band on soybean production.

Stratification of immobile nutrients in a no-till planting system has been documented in various studies (Robbins and Voss, 1991; Mallarino and Ul-Haq, 1997; Holanda et al., 1998). With no soil disturbance, stratification in no till systems should not be a surprise. With the ridge-till systems, however, there is disturbance when the corn crop is cultivated. The impact of this cultivation on distribution of soil test values for K is not known. This is especially true for K placed in a subsurface band (Varsa and Ebelhar, 2000).

Recognizing the previously stated needs, this study was designed to evaluate the impact of: (i) direct application of K applied in a subsurface band on yield of corn and soybean, (ii) residual K from a subsurface band on yield of soybean, and (iii) use of K in a subsurface band on distribution of soil test K in the upper portion of the root zone.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
This study was conducted in 1996 and 1997 in fields of three cooperating farmers who had used the ridge-till planting system for eight or more years. Phosphate and potash had been applied in a subsurface band in the center of the ridge at least three times. Selected sites had soil test K values (1 M ammonium acetate extractant) of 140 mg kg^–1 or higher. Values of 140 mg kg^–1 or higher are currently considered to be in the high and very high range (Rehm et al., 2001).

Soil at the Blue Earth County site was classified as a Le Sueur clay loam (fine-loamy, mixed, superactive, mesic Aquic Argiudoll). For the Dodge County site, the soil was classified as a Kasson silt loam (fine-loamy, mixed, superactive, mesic Aquollic Hapludalf). At the Pope county site, the soil was classified as a Barnes loam (fine-loamy, mixed, superactive, frigid Calcic Hapludoll).

Each site had been planted to soybean in 1995. All sites were planted with corn in 1996 and soybean in 1997.

The study was designed to measure the effect of K applied in a subsurface band on corn production in 1996. The soybean crop was grown in 1997 to measure the effect of direct and residual K applied in the subsurface band.

For corn, K was applied in a subsurface band at rates of 0, 19, 37, and 56 kg ha^–1. The K was applied as muriate of potash (0-0-50) at a depth of 10 to 13 cm in the center of existing ridges. Application was made in November following harvest of the soybean crop in 1995.

The soybean crop that followed corn was used to evaluate the effect of direct and residual fertilizer K. To measure the residual effect of K supplied in a subsurface band, the K (supplied as 0-0-50) was applied at rates of 0, 37, 74, 111, and 148 kg ha^–1 in November of 1995 following soybean harvest. To measure the effect of direct fertilization with K on soybean production, 0-0-50 was used to supply 0, 19, 37, 56, and 74 kg K ha^–1 in a subsurface band in November of 1995 and 1996. With this treatment design, the total amounts of K applied for the soybean crop in the 2 yr of the study were equal. Yet, direct and residual effects of the subsurface band could be compared.

A coulter and knife assembly was used for the subsurface placement. The applicator was pulled through the control plots, but no fertilizer was applied.

Treatments were arranged in a randomized complete block design with four replications. Individual plots were 3 m (four 76 cm rows) wide and 15 m in length. For corn, the seeding rate was 79000 plants ha^–1. The seeding rate for the soybean crop was 444600 plants ha^–1. Corn and soybean varieties as well as programs for weed control were choices of the cooperating farmers and were not recorded.

All sites selected had a high or very high level of soil test P, so fertilizer P was not applied. For corn, all treatments received equal amounts of fertilizer N as anhydrous ammonia (82-0-0). The N rate was 135, 140, and 168 kg ha^–1 for the Blue Earth Co., Dodge Co., and Pope Co. sites, respectively.

Potassium uptake was measured during the growing season. For corn, six whole plants were collected from outside a premarked harvest area and dried at 45°C for approximately 3 d following collection. In addition, the leaf opposite and below the ear was collected at silking. With the soybean crop, the most recently matured trifoliate leaves (approximately 50 per plot) were collected at early bloom. All plant samples were analyzed for K (Fassel and Kneseley, 1974). Corn yields were measured by hand harvesting 6-m sections of the two center rows of each plot. A plot combine was used to harvest two center rows of soybean having a length of 12 m.

Grain samples were collected from each plot at harvest to adjust yields to the constant moisture content of 135 and 145 g kg^–1 for the soybean and corn crops, respectively.

Detailed soil samples were collected in the fall of 1995 before the initiation of the study and again in the fall of 1997. Soil cores (2.5 cm diameter) were taken in incremental depths of 0 to 7.5, 7.5 to 15.0, and 15.0 to 22.5 cm in a 7.5-cm spaced transect perpendicular and crossing the two center rows. With this sampling pattern, the first core was taken from the center of the ridge in Row 2. The last core was taken at a distance of 37.5 cm from Row 2 and 37.5 cm from Row 3. Three transects were taken from all plots of a selected treatment with soil cores being composited by layer and position.

Soil samples were collected before the application of K in a subsurface band (initial) and again following soybean harvest in Year 2 of the study. Three treatments (control, two direct applications of 74 kg K ha^–1, residual effect of 148 kg K ha^–1) were sampled. The inverse distance procedure (Kecklin, 1997) was used to describe the distribution of soil test K in the volume of soil sampled. Samples were air-dried and exchangeable K was determined using neutral 1.0 M ammonium acetate (Warncke and Brown, 1998).

All data were analyzed with analysis of variance (ANOVA) and regression statistical procedures (SAS Institute, 1988). Regression procedures were used to quantify the effect of rate of K applied. Analysis of variance was used to quantify the effect of frequency of application and the possible interaction between rate and frequency of application.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Corn Production
Corn yield at all locations in Year 1 was not significantly affected by rate of K applied in a subsurface band (Table 1). Weather extremes or crop pests did not adversely affect yields. The CV for each site was <10%, indicating that experimental variability was not a major concern.

During the early adoption of no-till and ridge-till planting systems, Macray et al. (1987) suggested that placement of immobile nutrients in subsurface bands may be desirable after several years of continuous use of those planting systems. In agreement with the results from Iowa (Mallarino et al., 1999) and South Dakota (Reidell et al., 2000) results from this study suggest that placement of K in subsurface bands is not necessary for all fields planted with no-till or ridge-till systems. Consistent with results from those studies; K in subsurface bands did not improve corn yields if soil test K measurements were greater than approximately 150 mg kg^–1.

Response to K in a subsurface band may or may not be observed when soil test K values are approximately 140 mg kg^–1. In this study, no response was measured when soil test K was 142 mg kg^–1 (Dodge County). Yet, in previous research in Minnesota (Rehm, 1995) there was a yield response to K in a subsurface band when the soil test K (0–20 cm) was 140 mg kg^–1. The data collected do not provide an exact explanation for the discrepancy. Previous research (Rehm, 1995), however, showed that corn hybrids responded differently to the subsurface application of K. Hybrids used in the previous research were different from the one used at the Dodge County site. Even though values for soil test K were nearly the same, a difference in corn hybrids may be the best explanation for the disparity in response.

Results from this study, however, are not in agreement with those reported from Illinois by Ebelhar and Varsa (2000) where responses to K were measured when soil test K was in the range of 210 to 280 mg kg^–1. The difference noted might best be explained by difference in the chemistry by K associated with the clay minerals that are dominant in soils in each region.

Corn plants were collected from each plot at 4 to 5 wk after emergence. Potassium uptake by the young plants was computed from dry weight and K concentration data. Potassium uptake increased curvilinearly with rate of applied K at two of the three sites (Fig. 1) . Measured uptake was different among sites, which may be due to differences in stage of growth when samples were collected. Samples were collected at the V3 growth stage at the Dodge County site (Hanway, 1971). For the Blue Earth and Pope County sites, corn was at the V4 to V5 growth stage. Potassium uptake by young corn plants was not correlated to corn yield (r = 0.332, 0.426, –0.249 for the Blue Earth, Dodge, and Pope county sites, respectively).

View larger version (24K): [in this window] [in a new window]   Fig. 1. Relationship between K uptake by young corn (Zea mays L.) plants and rate of K applied in a subsurface band.

In this study, the absence of a response to K in a subsurface band indicates that soil at all sites was capable of supplying K for optimum yield of the soybean crop. As with corn, soil test K values in excess of 140 mg kg^–1 would indicate that fertilizer K is not needed for soybean production. These results are consistent with current University of Minnesota fertilizer recommendations (Rehm et al., 2001).

Adequacy of soil supplied K for optimum soybean yield in these production environments was confirmed by K concentrations in the most recently matured trifoliates at early bloom (Tables 5 and 6). For all treatments at all sites, K concentrations were above the adequate levels reported by Karlen et al. (1982) and Hanway and Weber (1971).

Results from the detailed sampling procedure used at the sites in Blue Earth, Dodge, and Pope Counties are shown in Fig. 2, 3, and 4 , respectively. The statistical summary for a comparison of direct and residual applications of K is provided in Table 7.

View larger version (15K): [in this window] [in a new window]   Fig. 2. Soil test K in the upper 22.5 cm of the root zone at the (A) Blue Earth County site measured in the fall of 1995 and in the fall of 1997 for three selected treatments ([B] control, [C] two annual applications of 74 kg K ha–1 in the fall of both 1995 and 1996, [D] a single application of 148 kg K ha–1 in the fall of 1995). Lines drawn represent equal values of soil test K expressed as mg kg–1.

View larger version (16K): [in this window] [in a new window]   Fig. 3. Soil test K in the upper 22.5 cm of the root zone at the (A) Dodge County site measured in the fall of 1997 for these selected treatments ([B] control, [C] two annual applications of 74 kg K ha–1 in the fall of both 1995 and 1996, [D] a single application of 148 kg K ha–1 in the fall of 1995). Lines drawn represent equal values of soil test K expressed as mg kg–1.

View larger version (18K): [in this window] [in a new window]   Fig. 4. Soil test K in the upper 22.5 cm of the root zone at the (A) Pope County site measured in the fall of 1995 and in the fall of 1997 for three selected treatments ([B] control, [C] two annual applications of 74 kg K ha–1 in the fall of both 1995 and 1996, [D] a single application of 148 kg K ha–1 in the fall of 1995). Lines drawn represent equal values of soil test K expressed as mg kg–1.

At the Dodge County site, soil test K at all depth increments below the row was significantly affected by the frequency of application (Fig 3., Table 7). In all cases, higher values were measured when two direct applications of 74 kg ha^–1 were used. Differences at depths of 0 to 7.5 and 7.5 to 15.0 cm would be expected from a subsurface band application of fertilizer K. The subsurface band was placed at a depth of 10 to 12 cm. Higher values at the 15.0 to 22.5 cm depth at this position relative to the row would indicate downward movement of the K from the fertilizer band.

Except for distances of 7.5 and 37.5 cm from the row, soil test K for all segments at the Pope County site was higher when two direct applications (74 kg K ha^–1 each) were compared with the residual effect of a single application of 148 kg K ha^–1 (Fig. 4, Table 7). This is a substantial contrast to the results from the Blue Earth and Dodge County sites. The cooperating farmer in Pope County believed in using two aggressive cultivations to build a high ridge. Each cultivation mixed and moved a substantial amount of soil and this soil movement is the most reasonable explanation for changes in soil test K at a distance of 30 cm from the row.

The spatial pattern of the distribution of soil test K values at the end of the second crop year was not consistent for all sites. When compared with the control, placement of K in a subsurface band directly beneath the row produced an increase in soil test values for K at all sites (Fig. 2, 3, and 4). Two direct applications produced higher values than a single application, which supplied the same rate of K as two direct applications at the Dodge and Pope County sites (Fig. 3 and 4).

Although there were some minor differences, which can probably be attributed to the use of the inverse distance procedure, K in a subsurface band produced small changes in the distribution of soil test K at the Blue Earth County site (Fig. 2). When compared with the control, a single application of 148 kg K ha^–1 before the crop in Year 1 had a minor effect on soil test K at the Dodge County site (Fig. 3). However, two direct applications in the subsurface band increased soil test K at a depth of 7.5 to 15.0 cm.

Higher soil test values directly beneath the row or at a distance of 15.0 cm from the row might be expected. Except for soil movement during cultivation, there is no apparent explanation for higher soil test K values at this depth at a distance of 30.0 to 37.5 cm from the row.

At the Pope County site, soil test K values resulting from a single K application of 148 kg ha^–1 prior the crop in Year 1 were low (Fig. 4). At this time, there is no apparent explanation for this observation. Compared with the control, two direct applications of 74 kg K ha^–1 increased soil test K values at a depth of 0 to 7.5 cm. The cooperating farmer cultivated the crop each year and this observation might be expected.

In general, the portions of the root zone where use of K in a subsurface band increased soil test values correspond to the same segments where increased root growth in a ridge-till system has been measured (Oldham, 1997). Since large changes in soil test K were not measured at distances >15.0 cm from the row or depths >15.0 cm, it seems that collection of soil samples to a depth of 15.0 cm in a ridge-till planting system would be appropriate.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The results of this study provide a basis for improved management of K in ridge-till planting systems. Earlier research had demonstrated the importance of subsurface banding of K for this planting system. The yield data from this study, however, show that the subsurface application is not a universal requirement for all fields where ridge-till planting is practiced. At three sites, there was no increase in either corn or soybean production if the soil test value for K (0–15 cm) is 140 mg kg^–1 or higher.

The repeated banded application of immobile nutrients raises concerns for procedures used in the collection of soil samples. A detailed soil sampling procedure followed by analysis of soil samples for K showed limited movement of K from the placement of the band. There was little, if any, movement of K. The results of this detailed sampling support current suggestions that soil cores should be collected from a depth of 15 to 20 cm from the soil surface. These results also support current University of Minnesota suggestions for collection of soil samples from either ridge-till or closely related conservation tillage systems.

	ACKNOWLEDGMENTS

 
The authors gratefully acknowledge the financial support for this study provided by the Potash Corporation of Saskatchewan.

Received for publication July 24, 2002.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Rehm, G. W. Articles by Lamb, J. A. Search for Related Content PubMed Articles by Rehm, G. W. Articles by Lamb, J. A. Agricola Articles by Rehm, G. W. Articles by Lamb, J. A. Related Collections Soil Conservation Soil Fertility and Productivity Tillage