Interaction between Row Spacing and Yield

Search PMN

Interaction Between Row Spacing and Yield: Why it Works

Kurt D. Thelen, Department of Crop & Soil Sciences, Michigan State University, East Lansing 48824

Abstract

Agronomic research has indicated that there is a potential for yield increases with corn grown in row widths less than 30 inches. However, results are often inconsistent and the corn grain yield response to row width seems to be dependent upon a number of environmental and management factors. Very little work has been done to determine the factors that favor a positive yield response to narrow-row corn. The objective of this paper is to define conditions that favor a positive yield response to narrow-row corn. Research conducted in Michigan has shown that in three of four site years, the yield increase from decreasing the row width from 30 to 15 inches was greater on course-textured soils compared to a clay loam. On average the yield increase for the course-textured soils was 9.1 bu/acre versus 4.5 bu/acre for the finer-textured clay loam soils when row width was narrowed from 30 to 15 inches. This may be a result of increased water use efficiency with the narrow row widths under water-limiting conditions associated with the coarse-textured soils. In the presence of a significant environmental yield-limiting factor (e.g., low soil water availability) the efficiency achieved with more equidistant plant spacing is likely to result in increased yield due to the more efficient plant accumulation of resources (e.g., soil water) restricted by that environmental yield-limiting factor. Therefore, the yield response in switching to narrow rows would be expected to be greater under more challenging growing conditions compared to the yield response achieved in switching to narrow rows under more optimal growing conditions. Under more optimum growing conditions the gain from more equidistant spacing is negligible since the potential yield-limiting factors are available in abundance ("saturation") at the wider row spacing. The same concept can be applied to radiation interception. More efficient radiation interception may be the basis for the observed positive yield response to narrow rows in northern latitudes where light is a more yield-limiting factor compared to southern latitudes.

Introduction

The debate over the optimum row spacing for maximizing corn grain yield has gone on for a long time. One of the earliest references dates back to a book published in 1866 entitled Indian Corn, (4) where nonreplicated yields of 160 bu/acre and 165 bu/acre were reported for Kentucky and Ohio, respectively, using "rows 2 ft asunder, stalks 12 inches apart." Considering the time period, these yields were probably not corrected for moisture and their accuracy may be somewhat questionable by today’s standards. Nonetheless, the early year of publication provides a reference point for how long the optimum row width debate has been ongoing. There is general agreement that the primary determinant of crop row width over time has been the width of the field equipment power source. Mid-1960 (10) extension field demonstrations by University of Illinois, Extension Specialist, J. W. Pendelton, featured a life-size replica of the rear view of a draft horse placed betwixt a 40-inch row spacing of corn to demonstrate to growers the obsolescence of the 40-inch row. The on-farm transition from animal to machine propulsion during that time period fueled a flurry of research evaluating crop row widths less than the then-current standard of 40 inches. During this time period, Denmead et al. (3), reported that equidistant plant arrangement maximizes crop yield. The basis for the maximized yield with equidistant plant spacing was proposed to be a decrease in plant to plant competition for available water, nutrients, and light, resulting in increased radiation interception (RI) and biomass production. Intuitively, this makes sense, especially from an ecological standpoint. However, if it were explicitly true, a positive yield response to more equidistant plant arrangement would always be observable. However, the scientific literature shows a whole range of yield responses to row widths less than 30 inches. More recent results range from a slight negative yield response (5), a neutral response (8), to a 7% increase in narrow-row yield over wider rows as reported by Porter et al. (11). The greatest advantage with narrow-row systems seems to be in northern locations. Paszkiewicz (9) summarized 84 university and industry studies and reported corn grown north of the I-90 corridor responded on average with an 8% increase in yield when row width was narrower than 30 inches. Furthermore, Cox et al. (2) suggested that corn grown in narrow row widths north of 44°N latitude had a yield advantage over wider rows.

The disparity reported in the literature suggests that the yield response to narrow rows is affected by many environmental, spatial, and temporal field interactions. Therefore, an evaluation of the utility of narrow-row systems must characterize or index the conditions which favor a positive, neutral, or negative yield response to narrow rows. Early references on the utility of narrow-row systems suggest that a positive yield response will be favored when all other environmental yield-limiting factors are adequately addressed. For example, extension recommendations in the mid 1960s from Iowa State University (6) and Michigan State University (12) advise growers to "do all other practices efficiently, then narrow-row corn can boost yields 5 to 8 percent" and "narrow-row corn culture should be considered when all other corn production practices are being utilized to a maximum." However, in more modern scientific literature there is emerging support for the hypothesis that a positive yield response to narrow rows is more likely to occur in the presence of environmental yield-limiting factors. Andrade et al., (1), reported that the narrow-row yield response was inversely proportional to the radiation interception achieved with wider rows. Under very favorable growing conditions, when radiation interception for the wide rows was optimized, the yield response to narrowing the rows was minimized. Conversely, growing conditions that resulted in lower radiation interception for wide rows resulted in a positive yield response to narrowing the rows. This hypothesis can be used as the basis for the observed latitude affect described by Paszkiewicz (9). During a typical corn growing season, northern locations receive fewer growing degree units than more southern locations creating a relative yield-limiting condition in the North. If the decreased radiation interception occurs during a critical period for yield determination, the response to narrow rows in the northern areas would be expected to be greater. The longer day lengths associated with more northern latitudes, centered on the summer solstice (June 21), coincide with a critical period for corn grain yield determination. This is depicted in Figure 1, which shows the measured normalized differential vegetation index (NDVI) as affected by corn row width in a central Michigan corn field. As measured on June 21, the narrow-row corn (15-inch row width) has a significantly higher NDVI than the wide rows (30-inch row width). Later in the growing season when both row width systems achieve full canopy, the NDVI values equilibrate. However, the timing of the disparity in radiation interception coincides with a critical plant development period (V5 to V8) for corn grain yield determination. The observation that corn grown in narrow rows has greater leaf area and radiation interception during the time period associated with the longer day lengths in northern latitudes, serves as a basis for the more positive yield response to narrow rows in the northern corn belt.

Fig. 1. The northern latitude disparity in normalized differential vegetation index (NDVI) is present during the critical yield determination period in late June/early July but disappears when both row widths reach full canopy closure later in the growing season. The photographs provide a visual representation of the plots on the dates the NDVI data were taken. The data are from a 2004 replicated (n = 4) trial located in Mason, MI (latitude = 42°38"). Means followed by a different letter are significantly different at P = 0.05.

The hypothesis that a positive yield response to narrow rows is more likely to occur in the presence of environmental yield-limiting factors can be tested on diverse soil conditions as well. Areas of course-textured soil within fields often depress crop yield due to limited water availability (7). A course-textured soil with poor water holding capacity would result in an early-season crop canopy with a relatively lower radiation interception than that from a crop canopy of plants grown in a more productive soil. Therefore, the yield increase with narrow rows is expected to be greater in the poor soil even though overall yields would be greater in the more productive soil. The effect of soil type on the narrow-row yield response was evaluated at two locations (Monroe and Clinton Counties) over two years (2000-2001) in Michigan. The Monroe location had primarily a clay loam soil with a water holding capacity of 0.20 inches/inch of soil, and pockets of a loamy sand soil with a water holding capacity of 0.12 inches/inch of soil (14). The Clinton location was primarily composed of a loam soil (0.20 inches/inch) with pockets of soil classified as "sandy areas" (13). At each location, corn was grown in 30-inch rows and 15-inch rows on both soil types. In three of the four site-years, a greater positive yield response to narrow rows was observed in the course soils (Fig. 2) even though overall yields were greater in the more productive clay loam and loam soils. In these three site-years, the early-season wide-row LAI of corn on the course-textured soil was less than that of the corn grown on the fine-textured soil (Fig. 2). Conversely, adequate levels of early growing season precipitation at the Clinton location in 2001 resulted in there being no difference in the early-season LAI between the corn grown on the course or fine-textured soils. Consistent with the hypothesis, the Clinton 2001 site-year was the one site-year that there was not a greater yield response to narrow rows in the more coarse soil, due to the higher precipitation levels eliminating water availability as a yield-limiting factor. These results clearly support the hypothesis that a positive yield response to narrow rows is more likely to occur in the presence of environmental yield-limiting factors. However, if a drought stress were severe enough it may result in a negative yield response to narrow rows. The increased efficiency with which narrow-row plants accumulate water in the early development stages would result in the production of relatively more plant tissue, creating a greater potential sink in the narrow rows, and would also deplete the soil profile of water quicker than in the wide rows. If the drought stress persisted, the plant sink and water depletion in the soil profile would be increased in the narrow rows relative to the wide rows. Under these extreme conditions, a negative yield response to narrow rows would be expected.

Fig. 2. Affect of soil type on corn grain yield response to narrow rows. The numerical value above each site-year is the early-season wide-row (30 inch) LAI ratio between corn grown on the course soil versus fine soil plots.

The hypothesis that a positive yield response to narrow rows is more likely to occur in the presence of environmental yield-limiting factors was further tested by evaluating the results of a comprehensive narrow-row corn study published by Widdicombe and Thelen (15). This study conducted over multiple locations across Michigan from 1999 to 2001 resulted in 840 comparisons between 15-inch row and 30-inch row plots. Figure 3 shows a regression of the 15-inch row yields against the corresponding yield in 30-inch rows. The resulting linear regression, significant at the 0.001 level of probability, has a negative slope function, indicating that as the yield in the 30-inch row plot increases, the corresponding yield response to narrowing the rows decreases. In other words, when growing conditions were such that yields obtained in wide rows were favorable, the resulting yields obtained by narrowing the rows were relatively low. Conversely, when growing conditions were such that wide row yields were relatively low for the study, the corresponding yield response to narrowing the rows was relatively high.

Fig. 3. Affect of wide-row (30-inch) corn grain yield on the yield response to narrow rows.

Conclusions

Equidistant plant distribution decreases plant to plant competition for available water, nutrients, and light. In the presence of a significant environmental yield-limiting factor, the efficiency achieved with more equidistant plant spacing is likely to result in increased yield due to the more efficient plant accumulation of that rate-limiting factor. Therefore, the yield response to narrow rows would be expected to be greater under more challenging growing conditions. Conversely, under more optimum growing conditions the gain from more equidistant spacing is negligible since the potential yield-limiting factors are available in abundance ("saturation") at the wider row spacing. The timing and severity of temporally variable yield-limiting factors also interact with the yield response to narrow rows. The gained efficiency in nutrient, light, and water accumulation with narrow rows, as measured by vegetation indices, peaks prior to canopy closure. This coincides with the critical yield determining plant development stage of kernel row determination. More efficient radiation interception in northern latitudes during this critical yield determining stage may be the basis for the observed positive yield response to narrow rows in northern latitudes where light is a relatively more yield-limiting factor than in southern latitudes. Conversely, if a stress occurs later in the growing season following canopy closure and root development across the row for both row widths, or if the stress is catastrophically severe, the gain in efficiency with narrow rows is neutralized and the stress would have less of an affect on the yield response to narrow rows.

Literature Cited

1. Andrade, F. H., Calvino, P., Cirilo, A., and Barbieri, P. 2002 Yield response to narrow rows depend on increased radiation interception. Agron J. 94:975-980.

2. Cox, W. J., Cherney, D. R., and Hanchar, J. J. 1998. Row width, hybrid, and plant density effects on corn silage yield and quality. J. Prod. Agric. 11:128-134.

3. Denmead, O. T., Fritschen, L. J., and Shaw, R. H. 1962. Spatial distribution of net radiation in a corn field. Agron J 54:505-510.

4. Enfield, E. 1866. Indian Corn: Its Value, Culture, and Uses. D. Appleton and Company, New York.

5. Farnham, D. E. 2001. Row spacing, plant density, and hybrid effects on corn grain yield and moisture. Agron. J. 93:1049-1053.

6. Iowa State University Cooperative Extension Service, 1968. Profitable Corn Production. Pm-409. January 1968.

7. Jiang, P., and Thelen, K. D. 2004. Variability of soil and landscape properties and their relationship to crop yield in a north central corn soybean cropping system. Agron. J. 96:252-258.

8. Johnson, G. A., Hoverstad, T. R., and Greenwald, R. E. 1998. Integrated weed management using narrow corn row width, herbicides, and cultivation. Agron. J. 90:40-46.

9. Paszkiewicz, S. 1997. Narrow row width influence on corn yield. In: Proc. 51st Annu. Corn and Sorghum Res. Conf., Chicago, IL. Am. Seed Trade Assoc., Washington DC.

10. Pendelton, J. W. 1965. Turn old Dan around. Pages 16-17 in: Better Crops with Plant Food. Amer. Potash Inst., Inc. Washington D.C.

11. Porter, P. M., Hicks, D. R., Lueschen, W. E., Ford, J. H., Warnes, D. D., and Hoverstad, T. R. 1997. Corn response to row width and plant density in the northern corn belt. J. Prod. Agric. 10:293-300.

12. Rossman, E. C. 1965. Mich. State Univ., Dept. of Crop Scie. file no. 22.12.

13. USDA Soil Survey of Clinton County, Michigan 1978.

14. USDA Soil Survey of Monroe County, Michigan, 1981.

15. Widdicombe, W. D., and Thelen, K. D. 2002. Row width and plant density effects on corn grain production in the Northern Corn Belt. Agron. J. 94:1020-1023.