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Narrow row corn (Zea mays L.) forage producers in the northeastern USA grow corn at high plant densities and N fertility. We evaluated first year, second year, and continuous corn in field-scale studies at 30 and 15 in. row spacings at recommended final densities (~34,000 plants acre) and N fertility (~150 lbs/acre) and at 15 in. spacing at high densities (~40,000 plants acre) and N fertility (~200 lbs/acre) in 1998, 1999, and 2000 to demonstrate that narrow row corn forage does not require high densities and N fertility. The narrow row corn treatment at high densities and N fertility averaged the greatest soil NO3 -N concentrations in the upper 0.3 m depth at planting (37 ppm) and the fifth leaf stage of corn (61 ppm). Narrow row corn at high vs. recommended densities and N fertility had greater silage yield (24.1 and 23.3 tons /acre, respectively). Both treatments, however, had similar in vitro true digestibility (IVTD, 79.3 and 80.5%, respectively), neutral detergent fiber (NDF, 41.9 and 41.8 %, respectively), NDF digestibility (50.3 and 53.2 %, respectively) and whole plant N concentrations (1.06%). Furthermore, narrow row corn at high densities and N fertility averaged greater residual soil NO3-N concentrations (21 and 10 ppm, respectively). Narrow row corn forage producers must balance the benefit of greater yield with the risk of greater soil NO3-N losses when selecting plant densities and N fertility programs.
Abbreviations: DM, dry matter; GDD, growing degree days; IVTD, in vitro true digestibility; NDF, neutral detergent fiber; Vn, nth leaf stage.
Some large dairy producers in the northeastern USA adopted narrow row corn silage production in the mid-1990s. These producers, who believe that corn responds best to narrow rows under high plant densities and N, plant corn at about 50,000 plants acre and apply about 200 lbs/acre of N via animal waste application and previous legume crops in the rotation (Deibel, 1997). An additional benefit of growing narrow row corn silage under high N fertility is that these large dairy producers can dispose of additional animal waste, which is often in excess on their farms. In a recent study, however, Cox and Cherney (2001), reported no row spacing x plant density x N rate interactions for corn dry matter (DM) yield and forage quality. Consequently, they recommended the same harvest plant densities (32,000 to 34,000 plants/acre) and N fertility (150 to 160 lbs/acre) for corn silage at 15 and 30 in. row spacings in the northeastern USA. Most narrow row corn silage producers, however, have continued to plant at high plant densities and to apply high rates of animal waste.
Roth (1996) reported a 9% corn silage yield advantage at 15 vs. 30 in. row spacing in Pennsylvania. In New York, Cox et al. (1998) reported only a 4% corn silage yield advantage at 15 vs. 30 in. row spacing with no row spacing effect on IVTD, NDF, NDF digestibility and whole plant N concentrations. In the same study, the IVTD of corn in narrow rows had a negative linear response, the NDF had a positive linear response, and NDF digestibility had a negative quadratic response to plant densities. Cox and Cherney (2001) also reported that the IVTD of corn in narrow rows had a positive linear response and the NDF and NDF digestibility had negative linear-plus-plateau responses (plateau of ~100 lbs/acre) to N rates.
We evaluated first year, second year, and continuous corn forage at 15 and 30 in. row spacings at recommended harvest plant densities and N fertility and at 15 in. row spacing at high harvest plant densities (~40,000 plants/acre) and N fertility (~200 lbs/acre) on a large dairy farm in western New York. The objectives of the study were to evaluate (1) soil NO3-N and plant N concentrations at different times of the growing season, (2) DM yield, (3) forage quality, and (4) residual soil NO3-N concentrations under the different row spacings, plant densities, and N fertility. We formed a farmer-researcher partnership (Karlen et al. 1995) to conduct field-scale studies on a dairy farm with field-scale narrow row equipment and readily available dairy manure. A benefit of on-farm research is that it increases the credibility of the research among farmers, thereby improving adoption of the results (Anderson, 1992).
Field-scale studies were established on first year, second year, and continuous corn in 1998, 1999, and 2000 on a 600-cow dairy farm at an elevation of 1600 ft. near Warsaw, NY (42° 68′ N, 78° 22′ W). First year corn followed 3 years of alfalfa in the rotation in each year. Each selected field in 1999 and 2000 was not in the study in the previous year, except when first-year corn in 1999 became second-year corn in 2000, to avoid confounding place in the rotation with fields. The work crew on the farm performed all field operations, including applications of dairy manure, tillage practices, planting, spraying, and harvesting. The predominant soil type in the study was a Bath silt loam (coarse-loamy, mixed, mesic Typic Fragiochrepts). Soil test values in each of the fields during the spring of each year indicated a pH range of 6.6 to 7.0 and high soil test P and K values.
Three treatments (15 and 30 in. row spacings at final plant densities of about 34,000 plants/acre and N fertility of about 150 lbs/acre and 15 in. row spacing at final plant densities of about 40,000 plants/acre and N fertility of about 200 lbs/acre) were staked out in a randomized complete block design with three replications in each field in early spring of each year. Individual plot size was 40 ft. wide and 700 to 1200 ft. long. Dairy manure was analyzed each year for N, P, and K content just before manure application in early spring. Total N of the manure ranged from 0.3 to 0.35% with the organic N fraction in the 0.13 to 0.15% range and the NH4-N fraction in the 0.15 to 0.17% range . Liquid manure applications were then injected at rates of 61,000 to 12,000 gallons/acre (except for first year corn in the recommended N fertility treatment), depending upon N content of the manure, the year of corn in the rotation, and the N treatment, to achieve N fertility status of about 150 or 200 lbs/acre. All the fields in the study were plowed, disked, and harrowed in late April of each year.
Pioneer Brand ‘3523′ was planted in each field in late April in 1998 and in early May in 1999 and 2000 with a John Deere (Moline, IL) 15-row (20 ft. wide) narrow row planter at a rate of about 37,000 plants/acre for the recommended plant density and 45,000 plants/acre for the high plant density treatments. Two planting passes were made for each treatment. Alternate rows were shut off and the planter was adjusted for plant density when planting the 30 in. row spacing treatment. Continuous corn fields received an insecticide at planting for corn rootworm (Diabrotica sp.) control. Different preemergence broadcast herbicides were used, depending upon the weed history in the field, for weed control.
Final plant densities were estimated at about the 6-leaf (V6) growth stage (Ritchie et al., 1993) by counting all the plants in the fourth and fifth rows from one of the planting passes of each treatment. Final plant densities ranged from 32,000 to 34,000 plants/acre for the recommended plant density and from 40,000 to 42,000 plants/acre for the high plant density treatment. On the same day, soil samples from the 12 in. depth were taken from between rows 4 and 5 from the same planting pass at 50 ft. intervals along the entire length of each plot. Composite soil samples from each treatment were then sealed in plastic bags, placed in a cooler in the field, and then at the end of the day placed in a forced-air oven that was set at 60°C. After drying to constant moisture, the samples were analyzed for nitrate N colorimetrically with an autoanalyzer (Apken Corp., Klackamas, OR). Whole plant samples were taken on the same day (V6 stage) from row 5 and ear-leaf samples were taken at silking from row 4 at 50 ft. intervals from the same pass of each treatment. Samples were dried at 60° C in a forced air oven, and then ground in a Wiley mill. Plant N concentrations were then determined by Kjeldahl procedures (AOAC, 1990).
The entire length of the 11 center rows (13.8 ft.) in the 15 in. treatments and the center 6 rows (15 ft.) in the 30 in. treatment in the non-sampled pass were harvested with a narrow row chopper in mid to late September when the whole plant samples averaged about 30% of DM. The chopper blew the silage into trucks, previously tared for weight, and the trucks were then weighed on platform scales on the farm. Immediately after harvest, we harvested single plants at 50 ft. intervals from an unharvested row from the harvest pass from each plot. The plants were immediately chopped in the field with a small gasoline-powered chopper, sealed in plastic bags, weighed, and dried at 60° C in a forced-air oven until constant moisture. Soil samples from the upper 12 in. depth were taken at the same 50 ft. intervals and analyzed for nitrate N, as described previously.
The plant samples were ground sequentially through hammer and Wiley mills. Samples were then passed through a splitter, reduced to 50 g, and further ground through a cyclone mill (Udy Corp., Ft. Collins, CO, USA), fitted with a 1-mm screen. Samples (0.5 g) were analyzed by wet chemistry for whole plant NDF, according to procedures by Van Soest et al. (1991), and Kjeldahl N (AOAC, 1990). Samples (0.25 g) were also analyzed for IVTD, according to stage 1 of the procedure described by Marten and Barnes (1980). Samples were incubated for 48 h at 39° C in 5 ml of buffered rumen fluid containing 20 ml of the Kansas State buffer supplemented with 0.5 g urea/L. Following fermentation, residues were analyzed for NDF to determine NDF digestibility. The NDF digestibility was calculated as ([1-NDF residue at 48 h/initial residue] x 100).
Years were considered random and sites (first year, second year, and continuous corn) were considered fixed in the analysis of variance (ANOVA) model. A mixed model was used to analyze the data with General Linear Model (GLM) procedures using the SAS statistical software package (1992). Means among sites and among treatments for all measurements were separated by Fisher’s protected LSD (P=0.05).
Weather conditions differed markedly across growing seasons (Table 1). The 1998 growing season can be characterized as warm and wet, especially during the spring and early summer, with a total of 21 in. of precipitation and 2428 growing degree days (GDD) from May through September. The 1999 growing season can be characterized as warm and dry, especially during the spring and early summer, with a total of 16 in. of precipitation and 2432 GDD from May through September. The 2000 growing season can be characterized as wet and cool, especially during late spring and early summer, with a total of 25 in. of precipitation and 2100 GDD from May through September. Consequently, years had large MSE values in the ANOVA model (data not shown), and site x year interactions existed for most measurements. Surprisingly, site x treatment, treatment x year, and site x treatment x year interactions did not exist for any measurements.
When averaged across sites and years, the 15 in. row spacing treatment at high vs. recommended plant densities and N fertility averaged greater soil NO3-N concentrations in the upper 12 in. soil depth at planting and at the V6 stage (Table 2). Soil NO3-N concentrations at the V6 stage for all treatments, however, averaged about 50 ppm or greater, more than twice the critical concentration for optimum corn yields in the northeastern USA (Magdoff, 1991). Ma et al. (1999) reported that in Eastern Canada low mineral N losses occur from the rooting zone during the growing season in soils that receive repeated applications of dairy manure. The soils in this study have received dairy manure applications for decades so apparently low mineral N losses occurred on these soils during the growing season, even in the wet springs of 1998 and 2000.
When averaged across sites and years, corn at 30 in. row spacing had greater whole plant N concentrations at the V6 stage compared with corn at 15 in. row spacing and high plant densities and N fertility (Table 3). Corn at 15 in. row spacing and high plant densities and N fertility had the greatest DM accumulation at the V6 stage (data not shown), which probably diluted or lessened its whole plant N concentration. Whole plant N concentrations at the V6 stage for all treatments, however, averaged more than 4.1%, well-above the 3.5% critical concentration for optimum corn yield (Jones and Eck, 1973).
Likewise, ear-leaf N concentrations at silking, which did not differ among treatments, averaged about 2.6% (Table 3), above the critical concentration of 2.5% for optimum corn yields under high-yielding conditions (Dara et al., 1992). Ear-leaf N concentrations, however, averaged less than 2.4% in 2000, despite abundant soil NO3-N concentrations and soil water. Apparently, the very cool conditions in July of 2000 limited N uptake, which resulted in low ear-leaf N concentrations.
When averaged across sites and years, whole plant N concentrations at harvest did not differ among treatments (Table 3). The similar whole plant N concentrations at harvest for corn at 30 and 15 in. row spacings under recommended plant densities and N fertility agree with previous research by Cox et al. (1998). The similar whole plant N concentrations at harvest for corn at 15 in. row spacing under recommended or high plant densities and N fertility, however, disagree with previous research by Cox et al. (1993), who reported greater whole plant N concentrations at harvest for corn as N fertility increased from 140 to 225 lbs/acre. Cox et al. (1998), however, reported that whole plant N concentrations at harvest decreased in corn at 15 in. row spacing as plant densities increased from 33,000 to 42,000 plants/acre. Conceivably, a positive response of whole plant N concentrations at harvest to increased N fertility may have been offset by a negative response to increased plant densities, which would result in similar whole plant N concentrations at harvest between the 15 in. treatments.
When averaged across sites and years, corn at 15 in. row spacing and high plant densities and N fertility produced the greatest yield at 24.1 tons/acre (Table 4). Also, corn at 15 in. row spacing vs. 30 in. row spacing at recommended plant densities and N fertility had a significant 4% yield advantage, which is consistent with the results of a previous small plot study reported by Cox et al. (1998). Cox and Cherney (2001), however, reported that row spacing x plant density x N rate interactions did not exist for yield. The 3.3% yield advantage for narrow row corn at high vs. recommended plant densities and N fertility indicates that dairy producers could benefit from growing narrow row corn at high plant densities and N fertility, provided that forage quality and environmental quality are not negatively affected.
When averaged across sites and years, treatments did not affect IVTD, NDF, and NDF digestibility (Table 5). The similar concentrations of IVTD, NDF, and NDF digestibility of corn at 30 vs. 15 in. row spacings at similar plant densities and N fertility are consistent with previous research by Cox et al. (1998). Cox and Cherney (2001), however, reported that IVTD concentrations of corn at 15 in. row spacing showed a positive linear response and NDF showed a negative linear-plus-plateau response to increased N fertility. In contrast to N fertility, IVTD concentrations of corn at 15 in. row spacing showed a negative linear response and NDF showed a positive linear response to increased plant densities (Cox et al., 1998). As with whole-plant N concentrations at harvest, the tendency for offsetting responses of IVTD and NDF to increased N fertility and plant densities may have resulted in similar forage quality characteristics between the 15 in. treatments.
When averaged across sites and years, 15 in. row spacing at high plant densities and N fertility had the greatest soil NO3-N concentrations after harvest (Table 2). As expected, the 30 and 15 in. row spacings at recommended plant densities and N fertility had similar soil NO3-N concentrations after harvest. Ma et al. (1999) reported that in Eastern Canada large amounts of mineral N are lost to the environment over the winter when high rates of dairy manure are applied. Undoubtedly, most of the 21 ppm of soil NO3-N in the 15 in. row spacing treatment at high plant densities and N fertility can potentially be lost to the environment in the northeastern USA, which has similar climatic conditions as Eastern Canada.
Impacts of Results/Outcomes
Dairy farmers in the Northeastern USA, who have adopted narrow row technology, can potentially increase yields by 3.3% with no effect on forage quality by increasing final plant densities from about 34,000 to 100,000 plants/acre and N fertility from about 150 to 200 lbs N/acre. Unfortunately, soil NO3-N concentrations after harvest can potentially double with an increase in N fertility from 150 to 200 lbs N/acre. When selecting plant densities and N fertility programs, narrow row corn silage producers must balance the potential benefit of greater DM yield with the potential risk of greater loss of soil NO3-N to the environment. If narrow row corn silage producers increase N fertility to 200 lbs N/acre, they should adopt management practices, such as the planting of a cover crop immediately after harvest, to minimize soil NO3-N loss to the environment. Another strategy to minimize NO3-N loss to the environment is to increase N rates from 150 to about 170 lbs N/acre because narrow row corn at high plant densities and N fertility vs. recommended plant densities and N fertility did take up more N (198 and 214 lbs N/acre, respectively) in a previous small-plot study (Cox and Cherney, 2001). The application of an additional 20 instead of 50 lbs N/acre to narrow row corn may provide most of the yield benefit and reduce the risk of soil NO3-N loss to the environment.
Areas needing additional study
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Jones, J.B., and H.V. Eck. 1973. Plant analysis as an aid in fertilizing corn and grain sorghum. In L.M. Walsh and J.D. Beaton (ed.) Soil testing and plant analysis. SSSA, Madison, WI.
Karlen, K.D., M.D. Duffy, and T.S. Colvin. 1995. Nutrient, labor, energy, and economic evaluations of two farming systems in Iowa. J. Prod. Agric. 8:540-546.
Ma, B.L., L.M. Dwyer, and E.G. Gregorich. 1999. Soil nitrogen amendment effects on seasonal nitrogen mineralization and nitrogen cycling in maize production. Agron. J. 91:1003-1009.
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