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a Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
b formerly Postdoctoral Research Associate, now at the Dep. of Agronomy, Univ. of Wisconsin
* Corresponding author (apmallar{at}iastate.edu)
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: BR, band/row zone • CI, confidence interval • IBR, interband/interrow zone • STK, soil-test K • STP, soil-test P
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Researchers have studied the distribution of P and K in soil after broadcast or shallow band fertilization (usually applied with the planter) in no-till fields (Kitchen et al., 1990; Robbins and Voss, 1991; Tyler and Howard, 1991; Howard et al., 1999) and shallow or deep banding for ridge-till fields (Borges and Mallarino, 2001, 2003; Rehm and Lamb, 2004). Because of both vertical and lateral nutrient stratification, these authors concluded that the sampling method should be based on the knowledge (or lack of knowledge) of bands location. However, Tyler and Howard (1991) concluded that the nutrient status of soils with band fertilization could be evaluated effectively with random sampling. No information of this type is available for fields managed with no-till and chisel-disk tillage having deep-band P and K fertilization. Deep banding will result in systematic vertical and lateral nutrient patterns that should impact soil sampling techniques, but effects of cropping and successive band applications over several years are unknown. Therefore, the objective of this study was to evaluate lateral and vertical soil P and K stratification after deep banding fertilizers for several years for corn–soybean rotations managed with no-till and chisel-plow tillage.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The trials evaluated several fertilizer rates and placement methods for no-till and chisel-disk tillage systems. Plot length varied across sites from 16 or 18 m. Plot width was 4.5 m (6-row plots) at Sites 1 and 2, and 6.0 m (8-row plots) in other sites. A split-plot treatment structure in a randomized block design with tillage in main plots, fertilization in subplots, and three replications were used in all sites. At all sites the chisel-disk treatment involved chisel-plowing only plots with corn residue in the fall and field cultivating all plots in spring. One pass with a light disk harrow sometimes was used before field cultivating at Sites 2, 3, and 5. The tillage implements were those commonly used by Midwest farmers and were of the same type across locations, although brands sometimes differed. The chisel-plow shanks were spaced 30 cm apart and tilled soil to a depth of 15 to 20 cm. The field cultivators had staggered toolbars with shanks with overlapping 20-cm wide sweeps and one or two toolbars with thin teeth that smoothed the soil surface. The field cultivators (and disk harrows used at Sites 2, 3, and 5) tilled soil to a depth of 8 to 12 cm. All tillage operations were parallel to crop rows and fertilizer bands, although the traffic direction was switched each year.
Two fertilization treatments were sampled from each P or K trial and tillage treatment. These treatments were a control (no P or K during 4 yr) and deep-band fertilization at 28 kg P ha–1yr–1 (triple superphosphate) or 66 kg K ha–1yr–1 (KCl). Fertilizers were deep banded each year before any tillage using the same commercial deep bander in all sites. The toolbar had vertical coulters and knives that applied fertilizer into 25 mm wide slits approximately 13 to 18 cm below the soil surface and spaced 76 cm. Two small coulters behind each knife covered the knife slit with soil. In deep-band plots, rows of both crops were placed on top of the coulter-knife tracks. Soil samples were collected after the fourth soy crop harvest (soybean). Separate samples (12 cores, 2-cm diameter each) were collected from each plot at 5-cm increments to a depth of 30 cm from the BR zone (a band was present only in fertilized plots) and the IBR zone. The BR zone was defined as a 20- to 25-cm swath centered in the crop row. The IBR zone was defined as a 20 to 25 cm swath centered between rows. Soil was dried at 40°C, crushed to pass a 2-mm sieve, and analyzed in duplicate for STP by the Bray-P1 test (Frank et al., 1998) and STK by the ammonium-acetate test (Warncke and Brown, 1998).
Tillage, fertilization, and sampling position differences for each site, nutrient, and sampling depth were assessed by a preliminary analysis of variance (ANOVA) for a randomized, split-split plot block design with three replication using the MIXED procedure of SAS (SAS Institute, 2000). The field design had tillage in main plots and fertilization in subplots, and for this study we assumed sampling position in sub-subplots. Soil-test values and variability always were much higher in fertilized plots (mainly in the 0- to 20-cm layer) because of the 4-yr fertilization histories. Therefore, to avoid statistical testing problems due to heterogeneity of variance and to simplify presentation of results, statistics presented are from ANOVA for each fertilizer rate and sampling depth.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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0.1) for STP (nine instances) or STK (10 instances) were small and inconsistent across 120 possible combinations of sites, tillage treatments, soil sampling depths, and row sampling positions for each nutrient. Therefore, only means across sites are shown for these nonfertilized plots in Fig. 1
. Figure 1A shows that STP tended to be lower for BR of no-till plots compared with other treatments for most sampling depths, but the difference was significant (P 0.1) only for two depths and was very small (3 mg P kg–1). Data for STK in Fig. 1B show the opposite trend, with higher STK for BR of no-till plots for most sampling depths, although the apparent large difference (at least 27 mg K kg–1 higher) for the shallowest depth (0–5 cm) was not significant. The STK differences for deeper depths were very small (11 mg K kg–1) and inconsistent.
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Tables 1 and 2 show effects of tillage and row sampling position on STP and STK of plots that received deep-band fertilization for each site and sampling depth. Numerically large and frequent soil-test differences between tillage and sampling positions for the three shallowest soil depths (<15 cm), but especially for the 5- to 15-cm depth, were confirmed by statistical analyses in few instances because of high variability. High soil-test variation in fields receiving band fertilization is well known. Statistical differences (P 0.1) always indicated higher STP and STK for BR compared with IBR with few exceptions (at Site 4 with chisel-disk tillage). This effect was almost always numerically larger for no-till than for chisel-disk tillage, and the tillage by sampling position interaction confirmed this result in a few instances. Soil-test P in the three deepest sampling depths (15–30 cm) was not affected by tillage and sampling position or differences were very small (Table 1). Significant STP differences (P 0.1) were observed only at Sites 4 and 5 for the 15- to 20-cm and 20- to 25-cm depths. At Site 4, STP was higher for BR than for IBR only with no-till whereas at Site 5 STP was higher for BR than for IBR with both tillage systems (but only in the 20- to 25-cm depth and by 1 mg P kg–1). Soil-test K differences between BR and IBR at the three deeper depths (Table 2) were slightly more frequent across sites and larger than for STP. Soil-test K was higher for BR than for IBR in the three depths at Site 1, in the 20- to 25-cm depth at Site 2, and in the 15- to 20-cm and 20- to 25-cm depths at Sites 4 and 5. These differences ranked similarly for both tillage systems.
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Analyses of soil-test means across sites provide a more general and more useful perspective because of the larger number of observations for a treatment or sampling position. Data for STP in Fig. 2A
show three obvious results. One result was that STP decreased with increasing sampling depth for both tillage systems, a trend that was also observed in nonfertilized plots. A second result was that STP in the shallowest soil depth (0–5 cm) was higher for BR with no-till (P 0.1) than for BR with chisel-disk tillage or IBR with either tillage systems (which did not differ). A third clear result was that STP was higher for BR than for IBR with either tillage system in sampling depths ranging from 5 to 15 cm and only with no-till for depths ranging from 20 to 30 cm.
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The most obvious dissimilarity between nutrients was that stratification was larger for STP than for STK. Concerning vertical stratification, calculations from data in Fig. 1A and 2A indicate that STP was four- to five-fold higher in the shallowest sampling depth than in the deepest depth while calculations from STK data in Fig. 1B and 2B indicate that STK was less than two-fold higher for similar depths. Concerning lateral stratification, average soil-test values across both tillage systems in the 5- to 10-cm depth, for example, were higher for BR than for IBR but were 100% higher for STP and only 35% higher for STK. Differences in vertical stratification between nutrients could be explained by differences in natural nutrient content and differences in crop nutrient uptake, recycling to the soil, and mobility in the soil. However, differences in lateral stratification between P and K ought to be explained only by differences in crop nutrient uptake and recycling to the soil. We speculate that a much higher crop uptake and recycling of K than P (Hanway et al., 1962) could partially explain the difference between nutrients. Borges and Mallarino (2001, 2003) observed similar differences in STP and STK lateral stratification for Iowa soils managed with ridge tillage and corn-soybean rotations.
The results of this study have important implications for soil sampling. Results for tilled or no tilled soil that received no deep-band fertilization for 4 yr and broadcast fertilization in the past agree with results from other Iowa corn and soybean fields reported by Robbins and Voss (1991) and from cotton fields reported by Howard et al. (1999) in that lateral STP stratification is of no practical concern. We observed similar results for STK, however, which do not agree with larger lateral STK stratification reported by Howard et al. (1999) for cotton fields. In our study, differences observed for both nutrients in these conditions represented a very small fraction of current Iowa soil-test interpretation classes (Sawyer et al., 2002) and sampling BR or IBR zones would seldom result in a different interpretation. The difference for STK between results from Iowa and those reported by Howard et al. (1999) may be explained by undetermined differences in soils and (or) crop species.
Results from plots that received deep-band P or K fertilization indicate that both vertical and lateral nutrient stratification should be of concern when sampling fields managed with no-till and chisel-disk tillage. This result is important because fertilization guidelines often recommend deep banding for no-till production (e.g., Hoeft and Peck, 2002; Sawyer et al., 2002) but no specific soil sampling method is recommended. Previous studies have addressed the problem of sampling stratified and highly variable no-till fields receiving broadcast or shallow planter-band fertilization and there are no straightforward solutions (Kitchen et al., 1990; Robbins and Voss, 1991; Tyler and Howard, 1991; Mallarino, 1996; Howard et al., 1999). An obvious result from this study is that a shallow soil sampling depth (i.e., 5–7 cm) sometimes recommended for vertically stratified no-till fields would not appropriately evaluate increased nutrient concentration down to a 15- to 20-cm depth due to deep banding. Therefore, the usual 15- to 20-cm sampling depth recommended for tilled soils would be applicable for fields managed with no-till or chisel-disk tillage and deep-band fertilization. The lateral stratification observed with no-till and deep-banding often encompassed two or three soil-test interpretation classes used in Iowa and other states. Some research has suggested collecting soil cores from the fertilizer band area of no-till or ridge-till systems when there is controlled traffic and the band location is approximately known (Kitchen et al., 1990; Borges and Mallarino, 2001, 2003). However, the bands location is uncertain when fertilizer bands are not parallel to and at a constant distance from crop rows or when banding was not used for the last crop. Previous research and our results suggest that in these conditions a random sampling pattern with more cores per composite sample than for fields receiving broadcast fertilization probably should be used.
We can only speculate about how the lateral stratification for the chisel-disk system would be if the tillage is done diagonally to deep bands and crop rows (for practical reasons producers do not till perpendicularly to crop rows). Our experience of many years suggests that diagonal tillage could probably result in more effective mixing of soil and disturbance of the deep bands depending on equipment type and operating depth but will not completely eliminate lateral stratification differences observed in this study.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Overall, this study indicated that vertical and lateral stratification due to deep-band fertilization should be of concern when planning soil sampling methods for for both no-till and chisel-disk management. A shallow soil sampling depth (i.e., 5–7 cm) sometimes recommended for no-tilled fields will not appropriately evaluate increased nutrient concentration at deeper depths due to deep banding. The usually recommended 15 to 20 cm soil sampling depth for tilled soils would be applicable for fields managed with no-till or chisel-disk tillage and deep-band fertilization. Previous research addressing sampling needs in fields with shallow bands and ridge-till fields with deep bands has suggested collecting soil cores from the band area when there is controlled traffic and the lateral band location is approximately known. The lateral stratification revealed in our study for fields managed with no-till or chisel-disk tillage and deep-band fertilization suggests that this recommendation probably also applies to these conditions. When the lateral bands location is uncertain or unknown, a random sampling pattern with more cores per composite sample than those recommended for fields receiving broadcast fertilization probably should be used.
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Received for publication April 21, 2005.
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REFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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This article has been cited by other articles:
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  A. P. Mallarino, S. R. Barcos, J. R. Prater, and D. J. Wittry Timing of Broadcast Phosphorus Fertilization for No-Till Corn and Soybean Soil Sci. Soc. Am. J., October 21, 2009; 73(6): 2143 - 2150. [Abstract] [Full Text] [PDF]
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 C. A. Jackson, J. M. Windes, P. Bregitzer, D. Obert, W. Price, and B. Brown Phosphorus Fertility Effects on the Expression of the Low Phytic Acid Barley Phenotype Crop Sci., August 7, 2009; 49(5): 1800 - 1806. [Abstract] [Full Text] [PDF]
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