WASTE MANAGEMENT

Published May, 2001

WASTE MANAGEMENT Characterization and Utilization of Nitrogen Contained in Sweet Corn Silage Waste Vincent A. Fritz,* Gyles W. Randall, and Carl J. Rosen ABSTRACT

the recent past, the industry was able to sell or donate a large amount of SCSW to livestock producers for feed. However, the decreasing number of feedlots has challenged the processing industry to find alternative ways to dispose of the SCSW in an environmentally responsible manner. Most processors have adopted the practice of land application as a means of disposal. State regulatory agencies have indicated that land application of these wastes should be done in an environmentally nondegradational manner and, due to the lack of any empirical information, may assume that all N contained within SCSW is quickly mineralized. This assumption would necessitate the application of very conservative rates of SCSW. However, because SCSW contains approximately 18% dry matter (DM), 1.2% N, and 0.26% P, more liberal rates will likely be applied in the major sweet-corn processing regions of the USA to maximize production efficiency. Supplementing land that receives SCSW with conventional fertilizers without knowing the availability of nutrients contained within agricultural wastes can increase the potential for pollution of soil and water resources. Food-processing wastes from vegetables, fruits, meats, and dairy products contain high concentrations of N and account for almost 35 000 t of N annually in the USA (Smith and Peterson, 1982). Application of this amount of N either through irrigation of waste water or through the distribution of solid wastes, requires a full understanding of how quickly the organic N contained within the waste is either mineralized or immobilized. Although the challenge to responsibly dispose of foodprocessing waste, such as SCSW, is critical to the industry, it is not a widespread biosolid waste-disposal concern due to its relatively small volume (Parr and Willson, 1980). As a result, research information on these types of agricultural wastes is extremely limited. A key factor affecting N fertilization strategies with organic wastes is the conversion efficiency of organic N to available N for crop growth. Organic solid waste materials with C/N ratios ⬎25:1 result in net immobilization of N, which could have a negative effect on subsequent plant growth (Paul and Clark, 1989). King (1984) found significant immobilization of N in a wide variety of industrial, municipal, and animal wastes having C/N ratios ⬎23:1. A similar land application study involving cocomposted sewage sludge with a C/N ratio of 35:1 resulted in net immobilization of N (Sims, 1990). Mamo et al. (1998) also found that corn yield response to com-

Sweet corn (Zea mays L. var. rugosa Bonaf.) silage waste (SCSW), a byproduct of the vegetable processing industry, accounts for 61 to 73% of the initial harvest yield. Concern relating to land application of SCSW has focused on the potential environmental impact of large quantities of mineralized N from the waste. This study was conducted to quantify the rate and amount of N mineralization from varying rates of SCSW applied to a fine-textured glacial till soil and to determine if nutrient contributions from SCSW can be integrated into a nutrient management system for subsequent crop production while enhancing environmental stewardship. Sweet corn silage waste was land-applied to main plots at rates of 0, 112, 224, 336, and 448 t ha⫺1 (fresh wt.) to a harvested sweet corn field and moldboard-plowed in early fall. Urea [(NH2 )2CO] was preplant broadcast-applied and incorporated to subplots at rates of 0, 67, and 134 kg N ha⫺1 in 1993; and 0, 83, and 166 kg N ha⫺1 in 1994 and 1995. Mineralization of N in the SCSW was assessed by NO3–N analysis of in-season and postharvest soil samples and by yield and N uptake of field corn. Spring temperature and precipitation greatly influenced mineralization of SCSW. In the wet, cold year, in-season NO3–N concentrations were lower and postharvest NO3–N was not affected by SCSW rate. Grain yield and N uptake were increased with increasing SCSW rate. In the warmer and drier years, in-season and postharvest NO3–N concentrations were much greater and were significantly increased by increasing SCSW rates. Corn grain yield and N uptake were optimized by a combination of SCSW and fertilizer N when SCSW rates were ⬍224 t ha⫺1. At rates ⬎224 t ha⫺1, mineralized N from the SCSW was sufficient to maximize yields. Nitrogen availability in the first year after SCSW application averaged about 16 to 18% of the total SCSW-N applied. Averaged across the 3 yr, soil test P was increased 2.6 mg kg⫺1 with each 112 t ha⫺1 SCSW rate, whereas soil test K was increased 14.2 mg kg⫺1 by each 112 t ha⫺1 SCSW rate. Land application of up to 224 t ha⫺1 SCSW was feasible, provided it was given the appropriate N credit before supplementing with N fertilizer.

T

he vegetable processing industry in the USA annually produces more than 194 500 ha of sweet corn, resulting in an estimated 1.5 million t of sweet corn silage waste (SCSW). Between 61 and 73% of the harvested sweet corn delivered to the processing center is collected as SCSW (U.S. Dep. of Commerce, 1989). Sweet corn silage waste is comprised of husk leaves, cob, discarded kernels, and a small amount of stalk. In V.A. Fritz, Univ. of Minnesota Southern Research and Outreach Center, 35838 120th Street, Waseca, MN 56093 and Dep. of Horticultural Science, Univ. of Minnesota, St. Paul, MN 55108. G.W. Randall, Univ. of Minnesota Southern Research & Outreach Center, Waseca, MN. C.J. Rosen, Univ. of Minnesota, Dep. of Soil, Water, and Climate, St. Paul, MN 55108. Contribution of the Minnesota Agric. Exp. Stn. *Corresponding author ([email protected]).

Abbreviations: DM, dry matter; SCSW, sweet corn silage waste; STK, soil test; STP, soil test P.

Published in Agron. J. 93:627–633 (2001).

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AGRONOMY JOURNAL, VOL. 93, MAY–JUNE 2001

post and soil amendments depended on the C/N ratio of the compost. Their results indicated that a low C/N ratio (⬍20:1) compost applied at 88 t ha⫺1 may be sufficient to meet the needs of the crop in the first year after application. When compost with a C/N ratio ⬎20:1 was applied at the same rate, additional N fertilizer would be needed to maximize yield potential. Another study involving solid waste from potato (Solanum tuberosum L.) processing operations resulted in high rates of N mineralization (Smith and Hayden, 1984; Smith, 1986). Empirical data are lacking regarding the rate and amount of N mineralization from SCSW. The main objectives of our study were to: (i) quantify the rate and amount of N mineralization from varying rates of SCSW application, (ii) determine the interactive effect of N fertilizer on N mineralization from SCSW, and (iii) determine if nutrient contributions from SCSW can be integrated into a nutrient management system for subsequent crop production while enhancing environmental stewardship. All results are based on effects occurring during the first cropping season following SCSW application. MATERIALS AND METHODS The study was conducted on a Nicollet clay loam (fineloamy, mixed mesic Aquic Hapludoll) in 1993 and 1995 and on a Webster clay loam (fine-loamy, mixed superactive Typic Endoaquoll) in 1994 at the University of Minnesota Southern Research and Outreach Center, Waseca, MN. Both soils were tile-drained at a 25-m spacing. Before land application of SCSW in September, sweet corn was produced on the experimental site using standard cultural practices. After harvest, the remaining stalk stubble in the field was chopped in preparation for application of SCSW that was obtained from a local vegetable processor located approximately 9 km from the research site. The SCSW was weighed into manure spreaders for each main plot and applied at rates of 0, 112, 224, 336, and 448 t ha⫺1 (fresh wt.). Immediately after application, the plots were moldboard-plowed for effective SCSW incorporation. The following spring, each main plot was divided into three subplots, and urea was broadcast-applied at rates of 0, 67, and 134 kg N ha⫺1 in 1993 and 0, 83, and 166 kg N ha⫺1 in 1994 and 1995, respectively. Each subplot size was 3 m wide (four 76-cm rows) by 17 m long. Immediately after urea application, the entire experimental area was field-cultivated. The experimental plot design was a split plot with four replications. Corn (‘Pioneer 3578’) was planted in late April or early May in 76-cm rows perpendicular to drain tiles at a population of 80 000 plants ha⫺1 using a four-row John Deere 7100 MaxEmerge planter. Because of high soil-test values, fertilizer P and K were not applied. Insecticide was used to control soilborne insects. Herbicides were broadcast-applied pre-emergence followed by timely cultivation to maintain weed control. Corn was harvested in mid-October of each year. Grain yield was determined by combine-harvesting 27.0 m of row from the center two rows of each plot. Stover yield was obtained by hand-harvesting a 4.6-m section from one of the two center rows. Subsamples of grain and stover were each dried in a forcedair oven at 60⬚C and then ground in a Wiley mill to pass through a 1-mm sieve. Tissue samples were digested using the Kjeldahl method (Bremner and Mulvaney, 1982), and total

N was determined using the diffusion conductivity method (Carlson, 1978). Soil samples consisting of five cores each were collected monthly (Apr.–July) to a depth of 90 cm from the 0, 224, and 448 kg ha⫺1 SCSW plots to follow changes in NO3–N content. All soil samples were forced-air dried at 50⬚C and crushed to pass through a 1-mm sieve. Nitrate-N was determined following extraction of soil samples with 2M KCl using the diffusion conductivity method (Carlson et al., 1990). Soil samples from the 0- to 1.5-m depth were collected in 30-cm increments from each plot after corn harvest using a Giddings probe to determine residual soil NO3–N. Daily air temperature and precipitation data were recorded from April through September at a site located about 1 km from the experimental locations. Data were statistically analyzed using ANOVA for a split-plot design (SAS Inst., 1988).

RESULTS AND DISCUSSION Dry matter, nutrient content, and C/N ratio analyses of SCSW for the 3-yr period are summarized in Table 1. The C/N ratio ranged from 36.1 to 37.1, which supports the anticipated immobilization of N from soil or fertilizer N. In addition, total Kjeldahl N, P, and K contents were relatively consistent across years, and nutrient loading rates from land application of SCSW were calculated for each year (Table 2). Temperature and precipitation information depicts the departures from a 30-yr normal (Table 3). In 1993, weather conditions were unusually cold and wet throughout the season. In contrast, the 1994 and 1995 growing seasons were warmer and drier, which was more conducive for crop growth and nutrient utilization.

In-Season Soil Nitrate-Nitrogen The unusually cool and wet weather in 1993 had a profound effect on in-season soil NO3–N accumulation in the 0- to 0.9-m profile that was not seen in 1994 or 1995. Soil NO3–N increased slightly with increasing rate of SCSW in April but decreased continually from May through July when fertilizer N was not added (Fig. 1). In addition, the decrease tended to be greatest for the highest SCSW rate. This decrease in NO3–N suggests that immobilization may have been occurring in combination with greater denitrification at the higher SCSW rates. Because monthly rainfall exceeded normal amounts by 66 to 97% in April through August, leaching losses of NO3–N were also likely. Crop uptake in late June and July also would have accounted for lower soil NO3–N concentrations. Adding 134 kg N ha⫺1 to the plots in early May resulted in a substantial increase in soil NO3–N for the 0 t ha⫺1 SCSW rate and much smaller Table 1. Dry matter (DM), nutrient analyses on DM basis, and C/N ratio of sweet corn silage waste (SCSW) used each year. Year†

DM

Total C

TKN‡

P

K

C/N

2.3 2.6 2.9

7.9 10.0 10.5

36.9 36.1 37.1

kg⫺1

1993 1994 1995

198 159 170

424 462 456

g 11.5 12.8 12.3

† SCSW applied fall of previous year. ‡ TKN, total Kjeldahl N.

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FRITZ ET AL.: NITROGEN CONTAINED IN SWEET CORN SILAGE WASTE

Table 2. Loading rates of N, P, and K in sweet corn silage waste (SCSW) applied each year. Year†

SCSW rate t

1993

1994

1995

N

ha⫺1 112 224 336 448 112 224 336 448 112 224 336 448

P kg

255 510 765 1010 228 456 684 912 234 468 702 936

K

ha⫺1 51 102 153 204 46 92 138 184 55 110 165 220

Table 3. Growing season temperature and precipitation departures from normal at Waseca, MN in 1993, 1994, and 1995. Departures from normal Month

175 350 525 700 178 356 534 712 200 400 600 800

† SCSW applied fall of previous year.

increases for the 224 and 448 t ha⫺1 rates later in May. The June sampling showed about a 50% reduction in NO3–N for the 0 t ha⫺1 rate compared with May, and there was little difference between the May and June samplings for the 224 and 448 t ha⫺1 rates. These data again suggest denitrification and leaching losses of the fertilizer N applied to the control plots; however, it is surprising that NO3–N reductions also did not occur for the higher SCSW rates. In 1994, soil NO3–N levels in the top 90 cm in April were much greater than in 1993 (note scale in Fig. 1 vs. Fig. 2) and did not consistently differ across SCSW application rates (Fig. 2). Soil temperatures may have been too cool for significant mineralization of the SCSW to occur. However, in May, soil NO3–N increased when 448 t ha⫺1 SCSW was applied. By June, soil NO3–N levels had decreased to between 42 and 63 kg ha⫺1. There was no difference in soil NO3–N levels between SCSW treatments when 166 kg N ha⫺1 as urea was applied just before planting. This is in contrast to 1993 when urea alone resulted in significantly greater NO3–N concentrations compared with treatments that received SCSW. The difference in NO3–N between the years was likely due to a warmer spring in 1994 and markedly drier conditions, especially in May and June (Table 3).

Apr. May June July Aug. Sept. Avg.

Apr. May June July Aug. Sept. Total

30-yr normal†

6.2 14.3 19.5 21.8 20.2 15.5 16.3

75 93 104 107 107 90 576

1993

⫺0.4 ⫺0.6 ⫺1.2 ⫺0.7 0.9 ⫺2.6 ⫺0.8

55 64 69 75 104 ⫺7 360

1994 Temperature ⴗC 1.1 1.5 1.7 ⫺1.7 ⫺1.0 2.3 0.7 Precipitation mm 66 ⫺50 ⫺20 18 20 20 54

1995

⫺1.3 ⫺0.9 2.1 0.2 2.9 ⫺0.4 0.4

19 ⫺7 ⫺23 27 9 13 38

† 1961–1990 normal period.

These data suggest an additive effect on soil NO3–N when applying fertilizer N to these SCSW rates without immobilization by the SCSW and that denitrification and leaching losses did not occur. In 1995, soil NO3–N levels in the top 90 cm in May were not affected by SCSW rates (Fig. 3). However, by June, mineralization of the SCSW resulted in an increase in NO3–N levels from about 75 kg ha⫺1 for the 0 t ha⫺1 SCSW rate to 125 kg ha⫺1 for the 448 t ha⫺1 rate. Soil NO3–N was reduced about 40% by July, likely due to crop uptake. When 166 kg ha⫺1 fertilizer N was added to the SCSW rates, soil NO3–N levels were increased by a factor of 2 in both June and July compared with the treatments where fertilizer N was not applied. Similar to previous years, applying supplemental N showed an additive effect with each increasing rate of SCSW. The addition of 166 kg N ha⫺1 to the 448 t ha⫺1 SCSW rate resulted in almost 250 kg ha⫺1 NO3–N in June, and soil NO3–N still remained above 180 kg ha⫺1

Fig. 1. Soil NO3–N in the 0- to 0.9-m profile as influenced by rate of sweet corn silage waste (SCSW) (0, 224, and 448 t ha⫺1 ) and fertilizer N (134 kg ha⫺1 ) in 1993. Vertical lines indicate the standard errors of the means.

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in July. These high levels of soil NO3–N are considered to be in excess of plant needs and are potentially susceptible to loss through leaching from the soil profile.

Corn Yields and Nitrogen Uptake In 1993, an increase in corn grain yield was observed with increasing SCSW rate when averaged across fertilizer application rates, especially for the 336 and 448 t ha⫺1 treatments (Table 4). Total DM increased about 25% with increasing SCSW rate when averaged across fertilizer application rates. Total DM and N removal were significantly greater in plots receiving 336 and 448 t ha⫺1 SCSW compared with the lower rates. The role of additional N fertilizer was very obvious when the responses to fertilizer rate were averaged across SCSW treatments (Table 4). Corn grain yield, total DM, and N uptake increased with increasing rate of fertilizer N.

In 1994, corn grain yield increased steadily with increasing SCSW application rates from 0 to 336 t ha⫺1 in the absence of any additional N fertilizer (Table 4). Additionally, yield, total DM, and N uptake increased as N fertilizer rate increased at SCSW application rates from 0 to 224 t ha⫺1. However, once SCSW rate reached 336 t ha⫺1, additional SCSW or N fertilizer had no effect on grain or DM yield and N uptake. Maximum corn grain yield, total DM, and N uptake were obtained at the 336 t ha⫺1 SCSW rate without additional N fertilizer. In 1995, grain yield, total DM yield, and N uptake were significantly affected by an interaction between SCSW and N rate. Grain yield increased by as much as 2.8 t ha⫺1 as SCSW rate increased from 0 to 448 kg ha⫺1 in the absence of any additional N fertilizer (Table 4). The grain yield increase was only 0.6 t ha⫺1 when 83 kg N ha⫺1 as urea was added with essentially no yield benefit to SCSW when 166 kg N ha⫺1 was added. Maximum total DM yield and N uptake were obtained at the 336 t


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Table 4. Grain and total dry matter (DM) yields and N uptake by corn as affected by rates of SCSW and fertilizer N. Grain yield

SCSW rate ha⫺1

t 0 0 0 112 112 112 224 224 224 336 336 336 448 448 448 Main effects SCSW rate, t ha⫺1 0 112 224 336 448 P⬎F LSD(0.05) Fertilizer N rate, kg ha⫺1† 0 83 166 P⬎F LSD(0.05) SCSW rate ⫻ N rate interaction P⬎F CV, %

Fertilizer† N rate kg

Total DM Yield

1993

1994

1995

ha⫺1

0 83 166 0 83 166 0 83 166 0 83 166 0 83 166

1993 t

1994

N uptake 1995

1993

ha⫺1

1994

1995

ha⫺1

3.4 4.2 5.8 3.7 4.6 5.7 4.4 5.2 5.7 5.9 5.5 6.7 5.9 6.0 6.8

8.5 10.7 11.6 9.7 11.0 11.9 10.5 11.5 12.0 11.5 11.1 11.8 11.3 11.2 11.3

5.1 8.0 8.2 6.8 7.6 8.3 7.2 8.2 8.4 7.8 8.3 8.3 7.9 8.6 8.0

6.3 7.8 10.0 6.4 8.3 9.9 7.3 8.4 9.6 9.5 9.9 11.3 9.3 10.4 10.5

13.7 17.0 18.2 15.3 17.3 19.2 16.1 17.7 18.1 17.9 17.7 18.4 17.8 18.0 18.0

10.0 14.0 14.4 12.4 14.0 14.7 13.0 14.7 14.5 14.9 14.5 14.7 13.3 14.8 14.2

56 69 91 63 80 93 78 88 97 101 103 120 101 110 117

kg 103 151 170 129 153 192 141 174 192 179 174 190 168 185 193

74 119 140 107 135 149 113 148 154 137 149 152 128 152 149

4.5 4.7 5.1 6.0 6.2 0.000 0.8

10.2 10.9 11.3 11.5 11.3 0.018 0.7

7.1 7.6 7.9 8.1 8.2 0.007 0.6

8.0 8.2 8.4 10.2 10.1 0.000 1.2

16.3 17.3 17.3 18.0 17.9 0.040 1.2

12.8 13.7 14.1 14.7 14.1 0.003 0.7

72 79 88 108 109 0.000 12

141 158 169 181 182 0.000 11

111 130 139 145 143 0.000 10

4.6 5.2 6.2 0.000 0.4

8.5 10.8 11.7 0.000 0.4

7.0 8.2 8.3 0.000 0.5

7.8 8.9 10.2 0.000 0.5

13.7 17.0 18.2 0.000 0.5

12.7 14.4 14.5 0.000 0.6

80 90 103 0.000 7

103 151 170 0.000 7

111 141 149 0.000 7

0.001 5.8

0.012 9.6

NS 9.5

0.010 4.5

0.002 6.7

NS 11.4

0.000 6.7

0.009 8.5

NS 12.0

† Rates used in 1993 were 0, 67, and 134 kg N ha⫺1.

ha⫺1 SCSW rate without additional N fertilizer, which was very similar to observations made in 1994.

Residual (Postharvest) Soil Nitrate-Nitrogen The interaction between SCSW rate and fertilizer N rate was not significant in any of the years (Table 5). Residual soil NO3–N following corn harvest was not affected by SCSW rate or fertilizer N rate in 1993. These results are most likely due to the extreme wet and cold season that led to very low rates of mineralization and high levels of immobilization and denitrification. In 1994, residual soil NO3–N was greater than observed in 1993 (Table 5). At SCSW rates ⱖ336 t ha⫺1, residual soil NO3–N was significantly greater than it was for the 0 or 112 t ha⫺1 rates when averaged across fertilizer N rates. Applying 166 kg N ha⫺1 resulted in significantly greater residual soil NO3–N compared with the 0 and 83 kg N ha⫺1 SCSW rates. Residual soil NO3–N in 1995 followed a positive linear trend with increasing rates of SCSW and N fertilizer (Table 5). This additional evidence again shows that applying SCSW contributes significantly to soil N and is available for plant uptake in the following crop season.

Soil Test Phosphorus and Potassium Soil test P (STP) and K (STK) increased significantly with the one-time application of SCSW. Averaged

across the 3 yr, STP increased 2.6 mg kg⫺1 with each 112 t ha⫺1 SCSW rate, whereas STK increased 14.2 mg kg⫺1 with each 112 t ha⫺1 SCSW rate (Fig. 4 and 5). When applying SCSW at the 448 t ha⫺1 rate (203 and 737 kg ha⫺1 P and K averaged across the 3 yr.), STP and STK increased 10.3 and 56.9 mg kg⫺1 over the control rate (0 t ha⫺1 SCSW), respectively. These data clearly show the influence of increasing rates of SCSW on STP and STK and the potential for annual applications of high rates of SCSW to raise STP and STK to very high levels.

Nitrogen Availability from Sweet Corn Silage Waste Nitrogen availability from the SCSW was determined and expressed as apparent recovery of SCSW-N in plant and soil from plots that did not receive any supplemental fertilizer N (Table 6). The apparent recovery of N in plant and soil from the 112 to 336 t ha⫺1 rates generally ranged between 13 and 22% and averaged 16.4% for 1994 and 1995. Nitrogen recovery increased markedly when a fertilizer N rate of 67 or 83 kg ha⫺1 was applied, especially at the 112 and 224 t ha⫺1 SCSW rates, again demonstrating the interaction between the SCSW rate and fertilizer N shown in Table 4. To assess N availability from SCSW in another way, total N uptake from SCSW at rates of 112, 224, and 336 t ha⫺1 without addi-

632


Table 5. Residual soil NO3–N in the 0- to 1.5-m profile as affected by rates of sweet corn silage waste (SCSW) and fertilizer N. Fertilizer N rate†

SCSW rate t ha⫺1 0 0 0 112 112 112 224 224 224 336 336 336 448 448 448 Main effects SCSW rate, t ha⫺1 0 112 224 336 448 P⬎F LSD(0.05) Fertilizer N rate, kg ha⫺1 0 83 166 P⬎F LSD(0.05) SCSW rate ⫻ N rate interaction P⬎F CV, %

0 83 166 0 83 166 0 83 166 0 83 166 0 83 166

Soil NO3–N 1993

1994

kg ha⫺1 103 108 99 134 108 158 87 100 85 123 90 175 87 163 91 164 99 190 94 182 91 178 101 222 121 188 115 186 125 244

Table 6. Apparent recovery of sweet corn silage waste (SCSW)-N and fertilizer N in the mature corn plant and 0- to 1.5-m soil profile after harvest as affected by rate of SCSW and fertilizer N application.

1995 31 39 62 46 70 82 55 93 121 72 109 139 105 117 165

103 87 92 95 120 NS –

136 45 136 67 176 92 198 109 210 131 0.041 0.000 57 24

100 98 106 NS –

151 63 160 87 202 116 0.000 0.000 16 9

Avg. rate of N application in 3-yr period SCSW†

Fert.‡ kg

0 0 0 239 239 239 478 478 478 717 717 717 953 953 953

Apparent recovery of N in plant and soil

Total

1993

1994

1995

0 78 156 239 317 395 478 556 634 717 795 873 953 1031 1109

– 13.4 29.8 ⫺3.5 1.9 6.2 1.1 3.5 5.7 4.7 4.2 6.9 6.2 6.1 7.2

% – 89.2 70.5 7.9 20.9 39.6 20.4 23.6 27.5 21.9 18.4 23.6 15.9 16.2 21.0

– 63.8 58.4 20.5 31.5 31.5 13.5 24.7 26.8 14.2 19.5 21.4 13.7 16.1 19.0

ha⫺1 0 78 156 0 78 156 0 78 156 0 78 156 0 78 156

† Actual rate of SCSW-N application for each year is shown in Table 2. ‡ Fertilizer N rates used were 0, 67, and 134 kg ha⫺1 in 1993 and 0, 83, and 166 kg ha⫺1 in 1994 and 1995.

In 1993, grain yield and N uptake were significantly affected by SCSW application rates when averaged over

fertilizer N rates or when fertilizer N was applied in the absence of SCSW. Because 1994 and 1995 were warmer and drier than 1993, grain yield and N uptake were affected by an interaction between SCSW rate and fertilizer N. Once SCSW was applied at levels of ⱖ224 t ha⫺1, additional fertilizer N had no consistent effect on grain yield and N uptake, which is most likely due to weather conditions that promote mineralization and minimize denitrification and loss through leaching. In contrast to 1993, soil NO3–N increased slightly in May and June (1994 and 1995, respectively) after applying 166 kg N ha⫺1 as urea just before planting when SCSW had been applied compared with the plots receiving urea alone. The difference in NO3–N between 1993 vs. 1994 and 1995 was likely due to warmer springs in both 1994 and 1995 and markedly drier conditions, especially in May and June (Table 3). These data suggest an additive effect on soil NO3–N when applying fertilizer N in addition to these SCSW rates without immobiliza-

Fig. 4. Impact of sweet corn silage waste (SCSW) rate on Bray P1 soil test P (STP).

Fig. 5. Impact of sweet corn silage waste (SCSW) rate on soil test K (STK).

NS 11.7

NS 14.8

NS 16.4

† Rates used in 1993 were 0, 67, and 134 kg N ha⫺1.

tional fertilizer N was plotted against N uptake from fertilizer N. In 1994, average available N from SCSW at rates of 112 and 224 t ha⫺1 was 16.5%. In 1995, the average available N from SCSW at the 112, 224, and 336 t ha⫺1 rates was 19.7% (Fig. 6).

SUMMARY


633

within SCSW can result in reduced fertilizer inputs and reduced risk of ground water and surface water pollution. In addition, one should not overlook the P and K loading that also results from land application of SCSW. Soil test P and STK were increased significantly by the one-time application of SCSW. Averaged across the 3 yr, STP was increased 2.6 mg kg⫺1 with each 112 t ha⫺1 SCSW rate, whereas STK was increased 14.2 mg kg⫺1 with each 112 t ha⫺1 SCSW rate. These data clearly show the influence of increasing rates of SCSW on STP and STK and the potential for annual applications of high rates of SCSW to raise STP and STK to very high levels. REFERENCES Fig. 6. Using the fertilizer N curve to determine N availability from sweet corn silage waste (SCSW) in the following crop growing season (1995).

tion by the SCSW and that denitrification and leaching losses did not occur. Residual soil NO3–N following corn harvest was not affected by SCSW rate or fertilizer N rate in 1993. These results are most likely due to the extreme wet and cold season that led to very low rates of mineralization and high levels of immobilization and denitrification. In 1994, residual soil NO3–N was significantly greater for SCSW rates ⱖ336 t ha⫺1 than for the 0 or 112 t ha⫺1 rates when averaged across fertilizer N rates. In 1995, additional evidence showed that SCSW is a significant contributor of soil N that is available for plant uptake in the following crop season. In both 1994 and 1995, approximately 16 to 18% of the total N contained within SCSW was available the following year. Nitrogen mineralization from SCSW can be beneficial if appropriate credits are integrated into the management of the total N fertility requirements for the subsequent crop. From this study, it appears that land application of up to 224 t ha⫺1 SCSW would be feasible, provided it was given the appropriate N credit and supplemented with fertilizer. Sweet corn silage waste rates ⬎224 t ha⫺1 could result in N mineralization in excess of crop needs (field corn) if supplemented with additional N fertilizer. Effective management of N contained

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