Published in Agron J 99:1345-1351 (2007)
DOI: 10.2134/agronj2006.0350
© 2007 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Fertilizer Management
Nitrogen Management of Brown Midrib Sorghum x Sudangrass in the Northeastern USA
Quirine M. Ketteringsa,*,
Jerry H. Cherneya,
Greg Godwina,
Tom F. Kilcerb,
Peter Barneyc and
Sam Beera
a Dep. of Crop and Soil Sciences, Bradfield Hall, Cornell Univ., Ithaca, NY 14853
b Cornell Cooperative Extension of Rensselaer County, 61 State St., Troy, NY 12180
c Cornell Cooperative Extension of St. Lawrence County, 1894 State Hwy. 68, Canton, NY 13617
* Corresponding author (qmk2{at}cornell.edu)
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ABSTRACT
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Brown midrib (BMR) forage sorghum [Sorghum bicolor (L.) Moench.] x sudangrass (Sorghum sudanense Piper) hybrids (S x S) have been considered as a possible forage alternative to maize silage (Zea mays L.) where maize planting is delayed due to wet soil conditions. Our objective was to determine the most economic rate of nitrogen (MERN) for BMR S x S grown in a two-cut management system with a split application of N. Six field trials were conducted in New York in 2003 and 2004. One trial followed a grass–legume sod; a second trial had received liquid manure 19 mo before S x S planting. The remaining four followed S x S, silage maize, and/or a small grain crop. The MERN ranged from 137 to 192 kg N ha–1 cut–1 with dry matter (DM) yield ranging from 7.8 to 9.7 Mg ha–1 at the sites without additional N input. At the sites with prior N inputs, yield was higher (10.4–13.8 Mg ha–1) and MERN lower. The apparent nitrogen recovery (ANR) at the MERN was highest (61–73%) for the sites with prior N inputs. Nitrogen application rates > 145 kg N ha–1 cut–1 decreased nitrogen use efficiency (NUE) to <15 kg DM kg–1 N, while the ANR became <45%. We concluded that the MERN for BMR S x S grown in New York in a two-cut system following maize, small grains, or forage S x S is 125 to 145 kg N ha–1 cut–1. For sites that follow sod plow-down or recent manure application, N application rates should not exceed 40 to 60 kg N ha–1 cut–1.
Abbreviations: ANR, apparent nitrogen recovery • BMR, brown midrib • DM, dry matter • MERN, most economic rate of nitrogen • NUE, nitrogen use efficiency • S x S, sorghum x sudangrass hybrids
Received for publication December 11, 2006.
Nitrogen Management of Brown Midrib Sorghum x Sudangrass in the Northeastern USA
Quirine M. Ketteringsa,*,
Jerry H. Cherneya,
Greg Godwina,
Tom F. Kilcerb,
Peter Barneyc and
Sam Beera
a Dep. of Crop and Soil Sciences, Bradfield Hall, Cornell Univ., Ithaca, NY 14853
b Cornell Cooperative Extension of Rensselaer County, 61 State St., Troy, NY 12180
c Cornell Cooperative Extension of St. Lawrence County, 1894 State Hwy. 68, Canton, NY 13617
* Corresponding author (qmk2{at}cornell.edu)
Received for publication December 11, 2006.
Brown midrib (BMR) forage sorghum [Sorghum bicolor (L.) Moench.] x sudangrass (Sorghum sudanense Piper) hybrids (S x S) have been considered as a possible forage alternative to maize silage (Zea mays L.) where maize planting is delayed due to wet soil conditions. Our objective was to determine the most economic rate of nitrogen (MERN) for BMR S x S grown in a two-cut management system with a split application of N. Six field trials were conducted in New York in 2003 and 2004. One trial followed a grass–legume sod; a second trial had received liquid manure 19 mo before S x S planting. The remaining four followed S x S, silage maize, and/or a small grain crop. The MERN ranged from 137 to 192 kg N ha–1 cut–1 with dry matter (DM) yield ranging from 7.8 to 9.7 Mg ha–1 at the sites without additional N input. At the sites with prior N inputs, yield was higher (10.4–13.8 Mg ha–1) and MERN lower. The apparent nitrogen recovery (ANR) at the MERN was highest (61–73%) for the sites with prior N inputs. Nitrogen application rates > 145 kg N ha–1 cut–1 decreased nitrogen use efficiency (NUE) to <15 kg DM kg–1 N, while the ANR became <45%. We concluded that the MERN for BMR S x S grown in New York in a two-cut system following maize, small grains, or forage S x S is 125 to 145 kg N ha–1 cut–1. For sites that follow sod plow-down or recent manure application, N application rates should not exceed 40 to 60 kg N ha–1 cut–1.
Abbreviations: ANR, apparent nitrogen recovery • BMR, brown midrib • DM, dry matter • MERN, most economic rate of nitrogen • NUE, nitrogen use efficiency • S x S, sorghum x sudangrass hybrids
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INTRODUCTION
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ENVIRONMENTAL MANAGEMENT OF NUTRIENTS on dairy farms is essential for the long-term sustainability of the dairy industry. On productive agricultural land under good growing conditions, it is difficult to exceed the DM yields of maize for forage. However, delay in maize planting due to wet springs and drought during the growing season can result in substantially lower yields. Sorghum x sudangrass hybrids grow optimally when the temperature is between 25 and 30°C (Fribourg, 1995) and are better adapted to drought. The introduction of the BMR gene increased silage quality (higher protein content and digestibility) making BMR S x S a potential high quality alternative to maize in situations where maize production is compromised due to poor soil resources and/or extreme weather (Kilcer et al., 2005; Beyaert and Roy, 2005).
McLaughlin et al. (2004) and Sleugh et al. (2006) concluded S x S can produce high quality forage and be a good option for nutrient management (nutrient removal) in the southeastern USA. When grown as an annual forage crop in a two-cut system in rotation with winter rye (Secale cereale L.) and triticale (xTriticosecale Wittmack), S x S hybrids have the added environmental benefit of reduced erosion as compared with a maize crop (USDA NRCS, 1995). Furthermore, on dairy farms in the humid Northeastern USA, manure can be applied just before planting in June or following first cutting in July or August, when field conditions are less conducive to runoff and/or leaching than during maize planting time at the end of April or early May.
Since BMR S x S shows promise as an alternative to maize, agronomic best management practices for this crop for a wide variety of soil and climatic conditions need to be developed. In recent studies in New York, stand height management (Kilcer et al., 2005), nutrient removal (Ketterings et al., 2004, 2006), and K management (Ketterings et al., 2005) were evaluated. Preliminary studies in New York (Kilcer et al., 2002) and Eastern Canada (Beyaert and Roy, 2005) focused on N management for BMR S x S and showed that (i) N is often limiting DM production; and (ii) split-application of N increases NUE.
Beyaert and Roy (2005) concluded optimum yield and NUE occurred when 100 kg N ha–1 was applied split over two side-dress applications in a two-cut BMR S x S system and that the ANR and NUE decreased with increasing N rate ranging from 36 to 11 kg DM kg–1 N and 90 to 24%, respectively. In comparison, NUE and ANR for three perennial cool-season grasses grown in a three-cut system in Wisconsin were 9 to 28 kg DM kg–1 N and 17 to 50%, respectively (Zemenchick and Albrecht, 2002). No prior studies have been conducted to determine the MERN for BMR S x S in New York.
Our objective was to determine the MERN for forage BMR S x S grown in a two-cut management system in New York, based on data from five sites and 2 yr.
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MATERIALS AND METHODS
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Locations and Experimental Design
Six field trials were conducted in five counties in New York in 2003 (two trials) and 2004 (four trials). In 2003, an N x K field trial was established on a Volusia silt loam (fine loamy, mixed, active, mesic Aeric Fragiaquepts) at the Mt. Pleasant Research Farm in Tompkins County, New York, USA (Table 1). The site had medium P status (Table 2), and 50 kg P2O5 ha–1 was broadcast on all plots at planting. A split-plot design with four replicates was used with N application rate (0, 56, 112, 168, 224, and 280 kg N ha–1 per cut) as the main treatment in a randomized complete block design, and K application (0, 112, and 224 kg K2O ha–1 per cut) as subplots. Potassium application did not affect DM yield (Ketterings et al., 2005) so only the main effects of the N treatments will be discussed in this paper. Nitrogen was broadcast as (NH4)2SO4 at planting and after the first cutting. Plots were 1.8 x 4.5 m with a sampling and harvest area of 0.9 x 4.0 m. The trial followed a previous crop of BMR S x S in 2002 and wheat (Triticum aestivum L.) in 2001.
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Table 1. Soil series, cropping history and planting and harvest dates of six brown midrib sorghum x sudangrass trials in New York.
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Table 2. Initial soil fertility status (0–20 cm depth) and phosphorus and potassium fertilizer additions for six brown midrib sorghum x sudangrass trials conducted in 2003 and 2003 in New York.
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Another N rate trial was conducted in 2003 on an outwash derived Hoosic gravelly loam (sandy-skeletal, mixed, mesic Typic Dystrudepths) at the Valatie Research Farm in Columbia County, New York (Table 1), with five rates of N for each cut: 0, 56, 112, 168, 224 kg N ha–1 applied as urea. The equivalent of 29 kg P2O5 ha–1 was applied before planting (Table 2) to ensure sufficient P even though the site was classified as high in P. This trial also followed a previous crop of BMR S x S.
This was the only site with a dairy manure history; 26,500 L ha–1 of liquid manure were surface applied in November of 2001, 19 mo before S x S planting in the summer of 2002. This resulted in an application of about 345 kg ha–1 total N, 118 kg ha–1 P2O5, and a little over 300 kg ha–1 K2O that year. No additional manure application took place in 2003. Of the total amount of N applied with the manure in 2001, 51% was organic N of which 12% (21 kg ha–1) were expected to be available for plant uptake during the 2003 growing season (Ketterings et al., 2003). The trial was a randomized complete block design with four replicates. Plot size was 1.8 x 3.0 m with a harvest area of 0.9 x 1.5 m.
In 2004, four N rate studies were conducted in northern (St. Lawrence and Essex Counties) and central (Cayuga and Tompkins Counties) New York. Soils ranged from loamy fine sand in Essex County to silt loam in St. Lawrence County (Table 1). Each trial was set up as a randomized complete block design with four replicates and six N rates (0, 56, 112, 168, 224, and 280 kg N ha–1 per cut) applied as (NH4)2SO4. All sites were high in available P, but to assure sufficient P these sites received 22 to 50 kg P2O5 ha–1 (Table 2) at planting. The Essex site was low in K at the onset of the trial. This site received 90 kg K2O at planting while the other three sites were fertilized with 22 to 67 kg K2O ha–1 (Table 2). The plots were 1.8 x 8–9 m with a sampling and harvest area of 0.9 m x 7–8 m. Of the four 2006 trials, S x S at the St. Lawrence County site followed BMR S x S, similar to the 2003 sites. At the Cayuga site, S x S followed wheat in 2003 and barley (Hordeum vulgare L.) in 2002. At the Tompkins County site, S x S followed maize for silage in 2003 and barley in 2002, respectively. The site in Essex County was expected to have residual N credits as S x S followed spring plow down of a long-term grass–legume stand. None of the other 2004 sites had received N inputs beyond the N treatments imposed for the S x S study.
All trials were planted in the first 2 wk of June (Table 1) using a seeding rate of 77 kg seed ha–1. Precipitation and temperature during the growing seasons are shown in Table 3.
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Table 3. Monthly precipitation and temperature for six sites where brown midrib sorghum x sudangrass trials were conducted in New York in 2003 and 2004. Data were obtained from on site weather stations within 3.2 km (2 miles) of the plots (Northeast Regional Climate Center, 2006). The average monthly temperature is derived from calculated daily averages [(maximum – minimum)/2].
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Harvest
The BMR S x S was harvested at the end of July or early August and at the end of September (Table 1). Harvest was initiated when the plots that had received 168 kg N ha–1 had reached a stand height (measured as the distance between the surface of the soil and the horizontal curve of the tallest emerged leaf) of 0.90–1.10 m to optimize forage quality (Kilcer et al., 2005). Cutting height was 75–90 mm. Fresh wt. was determined and a subsample was taken to determine moisture content and N concentration. Samples were dried for 3 d at 65°C and ground using a cyclone sample mill (Model 3010–030, UDY Corporation, Fort Collins, CO) with a 1-mm screen.
Soil and Forage Analyses
Individual plots were sampled (0–20 cm) before planting. Samples were dried at 65°C, ground and passed through a 2-mm sieve before analyses at the Cornell Nutrient Analysis Laboratory, Ithaca, NY. Soil organic matter was determined by loss on ignition on exposure to 500°C (Storer, 1984). Soil pH was measured in a 1:1 (w/v) water extract. All plots were analyzed for available P, K, Ca, and Mg by shaking dried samples in a 1:5 (v/v) ratio for 15 min in Morgan solution (1 M sodium acetate buffered at pH 4.8) and filtering the extract through a Whatman No. 2 equivalent filter paper (Morgan, 1941). The extracts were analyzed using an Inductively Coupled Plasma Atomic Emission Spectrometer (JY70 Type II, Jobin Yvon, Edison, NJ).
The N concentration of the forage samples was determined by dry combustion according to Greweling (1976) using a Leco FP-528 C/N analyzer (Leco Instruments, Inc., St. Joseph, MI) at the Dairy One Forage Testing Laboratory, Ithaca, NY.
Statistical Analyses
Trials were analyzed individually using PROC MIXED of SAS (SAS Institute, 1999) with block effects as random effects and N rate as a fixed effect. Mean differences were considered significant if P 
0.05.
The MERN was defined as the N rate at which the highest DM returns to N fertilizer were obtained assuming a quadratic-plus-plateau model (PROC SREG, SAS Institute, 1999) given the N rate treatment effect was significant (P 0.05) and the R2 of the quadratic model was 0.50 or greater. This applied to five of the six sites. For the site with an R2 value < 0.50 the MERN was defined as equal to or less than the lowest N rate in the highest t-grouping for yield (P 0.05). A forage value of (USD) $110.25 Mg–1 DM and a fertilizer cost of $0.70 per kg N were assumed. All values are calculated and reported in U.S. dollars. Fixed costs were estimated at $440 ha–1. For each N application rate, NUE was determined as the increase in DM yield per kg N added (Eq. [1]) while the ANR was calculated as the N removal in harvest per kg N applied (Eq. [2]):
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RESULTS AND DISCUSSION
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Yield and Most Economic Rate of Nitrogen
In 2003, the MERN was 140 kg ha–1 cut–1 in Tompkins County for a yield of 8.3 Mg DM ha–1 (Table 4). For Columbia County, the MERN was 120 kg ha–1 cut–1 resulting in a yield of 13.8 Mg DM ha–1. The lower yields at the Tompkins County site most likely reflected lower temperatures caused by the high elevation (1650 m above sea level) of the site, and lack of rain in August that resulted in a low second cut DM yield (results not shown).
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Table 4. Most economic rate of fertilizer nitrogen (MERN), yield, nitrogen use efficiency (NUE), apparent nitrogen recovery (ANR), and return ha–1 at the MERN for brown midrib sorghum x sudangrass grown on six New York farm sites in 2003 and 2004. Optimum N rates were defined as the N rate with the highest return to N assuming a quadratic-plus-plateau yield model, fixed costs of (USD) $440 ha–1, a forage value of $110.20 Mg–1 dry matter (DM), and fertilizer cost of $0.70 kg–1 N. See Tables 1 and 2 for a description of the sites.
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In 2004, the MERN in Essex County (first year crop following grass–alfalfa plow down) was <56 kg N ha–1. This rate could not be determined more accurately due to a lack of treatments with N rates < 56 kg N ha–1. It was, however, obvious from these results that the long-term sod that was plowed down in the spring before planting of the BMR S x S supplied a large amount of the N required for optimum economic yield by the S x S. The average DM yield was 10.4 Mg ha–1 for N applications 
56 kg N ha–1.
For the other 2004 trials the MERN varied from 137 kg N ha–1 cut–1 in Cayuga County to 192 kg N ha–1 cut–1 in Tompkins County with DM yield at MERN ranging from 7.8 Mg DM ha–1 for the site in St. Lawrence County to 9.7 Mg DM ha–1 in Tompkins County (Table 4). These yields were consistent with those obtained in 2003 and in previous BMR S x S studies in New York (Ketterings et al., 2004, Kilcer et al., 2005).
The four sites without organic N history showed very similar responses to N addition; across all four sites, DM yield (Mg ha–1) showed a quadratic relationship with N application rate (N-rate in kg ha–1 cut–1):
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Sites varied greatly in economic return. In 2003, the return ($ ha–1) at the Columbia County site was more than three times greater than the return at the Tompkins County site, due to both lower yields and a higher MERN at the Tompkins County site. In 2004, return per hectare at the MERN ranged from $202 ha–1 in St. Lawrence County to >$640 ha–1 for the site with sod history in Essex County. The DM yields for the two sites with an organic history (Essex and Columbia County) were numerically higher than for the other sites at low to moderate N rates (Fig. 1
), and the return per ha at the MERN was considerably higher for both sites as well (Table 4), consistent with greater yields at equal N rates. These results support the observation that BMR S x S is highly responsive to organic inputs (both manure and sods).
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Fig. 1. Effect of N application (split equally between planting and the second regrowth period) on dry matter yield of brown midrib sorghum x sudangrass grown in a two-cut forage management system at six New York sites. See Tables 1 and 2 for a description of the sites.
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Yield and MERN at all sites in this study were considerably higher than the 5.9 Mg DM ha–1 yield at 100 kg N ha–1 MERN reported in Ontario (Beyaert and Roy, 2005). Temperatures during the growing seasons in New York and Ontario were similar (compare Table 3 with Table 2 in Beyaert and Roy, 2005). However, July, August, and September rainfall was considerably higher at New York sites than in two of the 3 yr of the study in Ontario (compare Table 3 with Table 1 in Beyaert and Roy, 2005), possibly explaining at least part of the yield and MERN differential. The higher MERN in the New York studies might also in part have reflected differences in N application methods; in the Ontario study, N was split between the six-leaf stage and following the first cut and knifed-in whereas in the New York studies, N was broadcast at planting and after first cutting.
The recommended N rate for topdressing of intensively managed (3–4 cuts) grass in New York varies from 224 to 252 kg N ha–1, whereas N rates for continuous maize grown on the six different soil types represented in the six BMR S x S trials vary from 96 to 149 kg N ha–1 depending on yield potential, soil N mineralization, and N uptake efficiency of the different soil types (Ketterings et al., 2003). Thus, based on DM yields, BMR S x S grown without additional sod or manure N inputs requires N rates more commonly applied to intensively managed perennial grass, twice the rate commonly applied to a maize crop.
Nitrogen Use Efficiency
Fertilizer NUE decreased with N application rate (Fig. 2
) for both cuttings and overall harvest although means were not significantly different among N rates for first cuttings in Columbia, St. Lawrence, and Essex Counties. The Tompkins County sites (both years) showed higher NUE for the first cutting at N rates lower than the MERN, possibly due to the higher elevation of these locations. Across all sites, the NUE of the first cutting decreased from 17.9 kg DM kg–1 N with addition of 56 kg N ha–1 to 6.7 kg DM kg–1 N with 280 kg N ha–1 cut–1 (Fig. 2). This decline in NUE was consistent with the decline from 16.2 kg DM kg–1 N with the addition of 25 kg N ha–1 to 2.7 kg DM kg–1 N at the rate of 82 kg N ha–1 in the studies by Beyaert and Roy (2005).
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Fig. 2. Nitrogen use efficiency as impacted by N application rate (split equally between planting and the second regrowth period) for brown midrib sorghum x sudangrass grown in a two-cut forage management system at six New York sites. See Tables 1 and 2 for a description of the sites.
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For the second cutting, our New York trials showed a maximum NUE of 37.4 kg DM kg–1 N at 56 kg N ha–1, similar to the 32.9 kg DM kg–1 N with 50 kg ha–1 N addition obtained by Beyaert and Roy (2005) in 1998 but higher than the maximum NUE of 7.8 and 20.9 kg DM kg–1 N in the same Canadian study in 1999 and 2000. Beyaert and Roy (2005) attributed the lower maximum NUE in 1999 and 2000 to hot and dry weather in 1999 and cooler and wetter conditions in 2000.
Averaged over both harvests and all sites, NUE decreased from 27.6 kg DM kg–1 N at 56 kg N ha–1 to 8.4 kg DM kg–1 N at 280 kg N ha–1 following a quadratic model (Fig. 2), very similar to the overall (3-yr) decrease from 36.7 kg DM kg–1 N at 50 kg N ha–1 to 11.4 kg DM kg–1 N at 221 kg N ha–1 in the study by Beyaert and Roy (2005). Yet, MERN and DM yield were at least twice those reported for the Canadian trial suggesting greater overall yield potential at the New York sites under the 2003 and 2004 growing conditions.
Zemenchick and Albrecht (2002) reported NUE values from 11 to 28 kg DM kg–1 N for three grasses grown in a three-cut system over two seasons at two Wisconsin locations. These results are very consistent with the 12 to 33 kg of DM kg–1 N at the MERN for BRM S x S in our studies, most likely because S x S continues to accumulate biomass under dry late summer conditions while grasses showed greatly reduced third-harvest yields (Zemenchick and Albrecht, 2002).
Nitrogen Concentrations and Uptake
Low N concentration (<10 g N kg–1 DM) was measured for first cutting when no additional N was added in Essex County only (Table 5), most likely a dilution effect due to the high DM yields for the first cutting at that site (data not shown). The N concentration of first cutting without N addition ranged from 9.8 to 16.3 g N kg–1, substantially lower than the 20.8 to 24.7 g N kg–1 for first cutting reported by Beyaert and Roy (2005). Nitrogen application increased N concentrations for all sites, but the extent of this increase varied from location to location (Table 5). Nitrogen removal ranged from 40 kg N ha–1 without N addition in Tompkins County in 2004 to 377 kg N ha–1 with 224 kg ha–1 N addition in the Columbia County site, consistent with the 251 to 393 kg of N ha–1 uptake reported for forage S x S by McLaughlin et al. (2004).
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Table 5. Nitrogen concentration and removal as impacted by N fertilization rate in six brown midrib sorghum x sudangrass studies in New York. See Tables 1 and 2 for a description of the sites.
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The MERN calculations did not take into account the higher N concentration with increasing N application. If this increase in forage value could be taken into account, the increase in N concentration beyond MERN for DM production could result in a slightly higher MERN.
Apparent Nitrogen Recovery
For the second cutting, all but one site (Tompkins County 2003 trial) showed a higher initial ANR and a sharper decline with N application for second cutting as compared with the first cutting (Fig. 3
). Where no N was added, the Columbia (manure history) and Essex County (sod history) sites showed the largest ANR. Furthermore, the ANR at the MERN for these two sites with prior organic N input was 1.5 to 2 times the ANR of the other four sites (61–73% vs. 29–43%, Table 4), once again suggesting great responsiveness of the crop to organic nutrient history. Beyaert and Roy (2005) concluded that S x S has a great capacity to utilize N at low N rates but a small capacity to utilize N at the higher N rates. Our results seem consistent with this observation.
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Fig. 3. Apparent N recovery as impacted by N application rate (split equally between planting and the second regrowth period) for brown midrib sorghum x sudangrass grown in a two-cut forage management system at six New York sites. See Tables 1 and 2 for a description of the sites.
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The ANRs of the four trials that did not have a manure or sod history (29–43%) were similar to the 17–50% obtained for three grasses in a study in Wisconsin (Zemenchick and Albrecht, 2002), slightly lower than the 49% for a three-cut system, and 59% for four-cut management of three cool-season grasses in Pennsylvania (Hall et al., 2003), and substantially lower than the 68% reported in the Ontario S x S study (Beyaert and Roy, 2005). These differences might be due to site differences in yield potential (higher in New York than in Ontario), harvest intensity (two-, three-, or four-cut systems), and application method differences (in the S x S studies, N was broadcast at planting and after first cutting in New York and knifed into the soil at the six-leaf stage and following first cutting in Ontario). However, additional research is needed to determine the impact of different N application methods on NUE of BMR S x S grown under similar conditions.
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CONCLUSIONS
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Our study suggests optimum N rates of 125 to 145 kg N ha–1 cut–1 for BMR S x S grown without further N (manure, sod plow-down) inputs beyond N released from soil organic matter. Averaged over four sites with no manure or sod history, N application rates > 145 kg N ha–1 resulted in NUEs of 15 kg DM kg–1 N or less, and ANRs < 45%. For sites that follow sod plow-down or recent manure application, N application rates should not exceed 40 to 60 kg N ha–1 cut–1.
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ACKNOWLEDGMENTS
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We thank Leon Hatch, Kelly Reardon, and Andy Durow for assistance with harvesting and soil and plant sample processing, and Francoise Vermeylen for help with the statistical analyses. This research was funded with grants from the Northern New York Agricultural Development Program (NNYADP), the Northeast Region Potash and Phosphate Institute, and Garrison and Townsend, Inc. Ammonium sulfate was donated by Honeywell, Inc., and seed was supplied by Agriculver Seeds.
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REFERENCES
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ABSTRACT
INTRODUCTION
