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Published online 12 October 2005
Published in J Environ Qual 34:2045-2051 (2005)
DOI: 10.2134/jeq2005.0015
© 2005 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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TECHNICAL REPORTS

Waste Management

Nitrogen Fertilizer Recommendations for Corn Grown on Soils Amended with Oily Food Waste

M. T. Rashid* and R. P. Voroney

Land Resource Science, Univ. of Guelph, Guelph, ON, Canada N1G 2W1

* Corresponding author (trashid{at}uoguelph.ca)

Received for publication January 17, 2005.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Soil and plant indices of soil fertility status have traditionally been developed using conventional soil and crop management practices. Data on managing N fertilizer for corn (Zea mays L.) produced on soils amended with C-rich organic materials, such as oily food waste (OFW) is scarce. Identification of a reliable method for making N fertilizer recommendations under these conditions is imperative. The objective of this research was to evaluate soil NO3–N (0- to 30-cm depth) at preplant and presidedress (PSNT) times of sampling for predicting N requirements for corn grown on fields receiving OFW. Experiments were conducted at two locations in Ontario, Canada over 3 yr (1995–1997) where OFW was applied at different rates (0, 10, and 20 Mg ha–1), times (fall and spring), and slope positions (upper, mid, and lower) within the same field. Presidedress soil NO3–N contents were higher compared with preplant time of sampling under all OFW management conditions. Corn grain yields were significantly affected by OFW management and N fertilizer application rates. Maximum economic rate of N application (MERN) varied depending on OFW management conditions. Presidedress soil NO3–N contents had a higher inverse relationship with MERN (r = –0.88) compared with soil NO3–N at preplant (r = –0.74) time of sampling. A linear regression model (Y = 180.1 – 8.22 NO3–N at PSNT) is proposed for making N fertilizer recommendations to corn grown on soils amended with OFW in this geographical region.

Abbreviations: FOG, fat, oil and grease • MERN, maximum economic rate of nitrogen • OFW, oily food waste • PSNT, presidedress soil nitrate N test


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
DEVELOPING AN ABILITY to predict the N requirements for maximizing economic corn crop production has been an important issue since N fertilizers became widely available. Increased public concerns about drinking water pollution with nitrates, and of emissions of the greenhouse gases such as nitrous oxides, have made it mandatory to justify N fertilizer recommendations both in economic and environmental terms. This resulted in more emphasis on N fertilizer use efficiency in recent years. Assessment of several soil and plant test methods that could improve N management for corn has been reported in the literature (Magdoff et al., 1984; Blackmer et al., 1989; Fox et al., 1989; Binford et al., 1990; Hong et al., 1990).

Early work (Soper et al., 1971; Olson et al., 1976) showed that yield response to applied N and crop N uptake were strongly affected by soil residual NO3–N. Soil NO3 tests are an effective method for identifying optimum N rates for corn in several cropping systems (Bundy and Andraski, 1995; Andraski and Bundy, 2002). Soil test based on NO3–N concentrations in the surface 30-cm layer of soil have successfully been used for N fertilizer recommendations for corn (Magdoff et al., 1984, 1990; Blackmer et al., 1989; Fox et al., 1989; Binford et al., 1992; Meisinger et al., 1992; Morris et al., 1993; Sims et al., 1995; Schroder et al., 2000). This sampling time is late enough to reflect the effects of spring weather conditions and early enough to apply fertilizer if needed.

Soil samples for NO3–N for PSNT are taken when corn is 15 to 30 cm tall and it has a very high demand for N. The rate of N uptake by corn is relatively slow before the plant enters the period of rapid growth at about the six-leaf stage. This stage usually occurs in early June (Corn Belt in USA) to early July (Ontario, Canada). The rate of N uptake by crop plants at this stage ranged from 2.5 to 4.5 kg ha–1 d–1 (Karlen et al., 1988). The presidedress NO3–N test performed during this high N demand by the corn crop is considered to be the most reliable soil N test to make an N fertilizer recommendation for corn (Magdoff, 1991; Binford et al., 1992, Vyn et al., 1999). Furthermore, PSNT soil NO3–N content represents the net balance between production (mineralization from soil organic matter, manure, and/or fertilizers) and loss (leaching, denitrification, and immobilization) because little or no N uptake occurs before this stage (Meisinger et al., 1992).

A variety of nonhazardous organic wastes can be applied to agricultural soils. One of these organic wastes is OFW produced by food service and food processing industries. This material contains high concentrations of fat, oil, and grease derived from animal and vegetable sources. The application of OFW, which has a high C/N ratio (90:1) will immobilize soil N and reduce plant-available N during its decomposition (Rashid and Voroney, 2004). Observations of high rates of decomposition and regular patterns of N immobilization and mineralization are common in studies involving different oils (Smith, 1974; Higuchi and Kurihara, 1980), volatile fatty acids (Kirchman and Lundvall, 1993; Sorensen, 1998), and OFW (Plante and Voroney, 1998). Nitrogen immobilized during the decomposition of fall-applied OFW (Rashid and Voroney, 2003) was subsequently mineralized and become available to the succeeding corn crop in spring (Rashid and Voroney, 2004).

Soil indices of soil fertility status have traditionally been developed using conventional soil and crop management practices. Published research resulting in N fertilizer management recommendations for corn produced on soils amended with C-rich organic materials such as OFW is scarce. Since additions of OFW may affect the short- and long-term soil N dynamics differently than net N-supplying organic wastes, recommendations based on conventionally tested methods may not be applicable.

Available N is released as a result of organic matter decomposition including crop residues, manure, composts, cover crops (Magdoff, 1991) and OFW (Plante and Voroney, 1998). Synchrony between NO3–N release and N demand by crop is one of the most important keys to understand N management options. By applying N close to the time of the crop's greatest need and when soil moisture tends to be below field capacity and evapotranspiration exceeds precipitation, there is a little possibility for loss by denitrification or leaching (Magdoff, 1991).

The objective of this research was to (i) determine the effect of land application of OFW on soil NO3–N levels at preplant and PSNT sampling times and (ii) determine the ability of soil NO3–N test for making N recommendations to corn grown on OFW-amended soils. The experiments conducted were designed to assess the effect of (i) rate of oily food waste application (Experiment 1); (ii) timing of oily food waste (Experiment 2); and (iii) location of application; slope positions (Experiment 3) on soil N fertility, N availability, and N requirements of the crop. The information generated for soils amended with this organic waste material will be useful to expand the knowledge regarding the use of soil NO3–N tests for N fertilizer recommendations for a wide range of crop and soil management conditions.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Description of Experimental Locations
The soils at different research sites have been mapped as Elora silt loam and Guelph loam (fine-loamy, mixed, mesic Glossoboric Hapludalfs) at the Elora Research Farm locations (Experiments 1 and 2) and Hilsburg fine sandy loam (Brunisolic Gray Brown Luvisol) at the on-farm locations in Bellwood (Experiment 3). Soil organic C, total N, NO3–N, extractable P, and K content in these soils are presented in Table 1.


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  		Table 1. Chemical properties of different experimental sites at Elora Research Station and Farmer's field in Bellwood (soil samples were taken from the 0- to 30-cm soil depth).

 
Experimental Designs
Rate of Oily Food Waste Application (Experiment 1)
This experiment was conducted at Elora Research Station at the University of Guelph, ON, Canada for 2 yr (1996 and 1997) in two separate plots. The experiment was set out in a split-plot design with four replications. Oily food waste was applied at 0, 10, and 20 Mg ha–1 to main plots (22.5 by 10 m) in late April in both years. Oily food waste was kept well mixed in a liquid manure tank (12000 L) and measured quantities were applied to individual plots using a 1000-L vacuum-operated slurry spreader. The surface soil was allowed to dry (2–4 h) before the OFW was incorporated in soil by moldboard plow. Nitrogen fertilizer treatments were assigned to subplots (4.5 by 10 m) and urea fertilizer was applied at 0, 50, 100, 150, and 200 kg N ha–1 at the time of field preparation for corn seeding. Field corn; hybrid Pioneer 3905 was planted (65000 seeds ha–1) on this location in the third week of May 1996 and 1997.

Time of Oily Food Waste Application (Experiment 2)
Experiment 2 was also conducted at Elora Research Station in 1996 and 1997 on two separate fields. The experiment was set out in a split-plot design with four replications. Oily food waste treatments including a control, OFW in fall (fall-applied OFW), OFW in spring (spring-applied OFW), and winter wheat cover crop (WWC) were assigned to main plots (22.5 by 10 m). Oily food waste at 10 Mg ha–1 was applied in early October (in fall) and in late April (in spring). Winter wheat cover crop was also included in the experiment as reference treatment in addition to the control to compare the effect of time of OFW application on soil NO3–N levels, corn grain yield, and MERN.

The winter wheat cover (Triticum aestivum L. cv. Harus) was planted on the same day that OFW was applied in the fall (1995 and 1996) and was incorporated in the soil on the same day that OFW was applied in spring (1996 and 1997). The total quantities of WWC fresh biomass (C/N = 14; mean value) incorporated in soil were 1.48 and 1.26 Mg dry wt. ha–1 for 1996 and 1997, respectively. Four samples of the cover crop (1 m2) from each replication were taken in mid-May before its incorporation in soil, and oven-dried (60°C) to determine the quantity of cover crop residue retained. Urea fertilizer treatments (0, 50, 100, 150, and 200 kg N ha–1) were assigned to subplots (4.5 by 10 m) and were applied at the time of field preparation for corn seeding during both years. The same hybrid and seed density of field corn was planted as in Experiment 1.

Slope Positions (Experiment 3)
The experiment was conducted on a farm field near Bellwood, ON, Canada for 2 yr (1995 and 1996) in two separate fields. The experiment was set out at upper (summit), mid (back slope), and lower (foot slope) positions as randomized complete block design with four replications. Oily food waste was stored in a liquid manure tank at the farm and was well mixed by using a tractor operated mixer. A commercial liquid manure application tanker was used to apply OFW in the field. Oily food waste was applied at 10 Mg ha–1 in late April during both years. The surface soil was allowed to dry (2–4 h) before the OFW was incorporated with a moldboard plow. Urea N fertilizer was applied at the time of field preparation at 0, 50, 100, 150, and 200 kg N ha–1 to plots (4.5 by 10 m) at each slope position. Field corn (hybrid DK-306) was planted (65000 seeds ha–1) during the third week of May in both years.

Oily Food Waste
Oily food waste used in these studies was collected from grease interceptors located in commercial and institutional food services outlets in the Greater Toronto area, Ontario, Canada. The waste consists of heterogeneous mixtures of animal and vegetable fat, oil and grease, water, and food-derived solids. Without mixing, the fluid quickly separates into four distinct layers: (i) a dark oily layer, (ii) over floating solids, (iii) over yellow-tinted water, and (iv) over settled solids. Grab samples of oily food waste were taken at four different times during its application in the field each year for chemical analysis.

The nonaqueous content (oil + solid contents) of the waste were determined by freeze drying at –30°C. The nonaqueous contents are organic because no grit or other fixed solids were found after ignition at 550°C. Total C, N, and oil contents were determined on waste samples that were freeze-dried at –30°C. Determination of total C content of the waste by direct combustion was not possible as samples exploded in the analyzer when ignited. Instead, total C in the residue left from soxhlet extraction was measured by dry combustion (Tiessen and Moir, 1993), and oil-C was calculated by assuming C in oil to be 90% of the molecular weight (Plante, 1996). The C content of the residue and oil were summed for OFW waste C content.

Total Kjeldahl N, pH, and electrical conductivity of OFW were also determined by following the methods described by McGill and Figueiredo (1993), Peech (1965), and Bower and Wilcox (1965), respectively. Oil contents were determined by placing OFW samples (5 g each) in cellulose thimbles and extracting with hexane for 24 h. Pre-weighed flasks containing the extracted oil were left open overnight to allow volatilization of the remaining hexane and then re-weighed to calculate the oil contents in OFW samples (Greenberg et al., 1995). Chemical composition of OFW applied at different locations is presented in Table 2.


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  		Table 2. Chemical analysis of oily food waste applied at different locations (Elora Research Station and on-farm) during 1995, 1996, and 1997.{dagger}

 
Soil Sampling and Analytical Procedures
Soil samples were taken from all locations for soil fertility analysis (Table 1). Soil samples (0- to 30-cm soil depth) were taken at preplant time of sampling and PSNT from the 0 N plots at all locations in 1995, 1996, and 1997. Preplant samples were taken before fertilizer applications and seeding (third week of May), and PSNT samples were taken at the N fertilizer side-dressing time (first week of July). Soil samples were immediately transported to the laboratory and kept at –8°C. Soil samples (field moist) were thawed and sieved through a 2-mm sieve and were extracted with 2 M KCl (1:5 ratio) at room temperature (Keeney and Nelson, 1982), and NO3–N and NH4–N were determined using a Braun + Lubbe TRAACS 800 instrument (Tel and Heseltine, 1990).

At maturity, two central rows (1.52 by 5 m; 7.6 m2) of each plot were hand harvested at all experimental locations to determine the corn grain yields. Ten subsamples of cobs were collected and oven-dried at 65°C. Oven-dried cobs were shelled and corn grain yield was calculated (expressed on 155 g kg–1 moisture content basis). Quadratic response equations for each replication of each experiment (Table 5) were used to calculate the MERN. The maximum economic rate of N fertilizer application was calculated by the following equation (McGonigle et al., 1996):

[1]
where b and c are second and third coefficients of quadratic response equation. The ratio of the price of 1 kg of fertilizer N to the price of 1 kg of corn grain is termed as R, whose value for use in the MERN calculations was assumed to be 7.


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  		Table 5. Quadratic response curves to determine MERN for all OFW management treatments.

 
Maximum economic rates of N values were correlated with preplant and PSNT soil NO3–N contents to determine the N requirements for corn grown on fields amended with OFW. The linear relationship equations between MERN and preplant and PSNT soil NO3–N content (0- to 30-cm depth) were used for making N fertilizer recommendations to corn grown on fields amended with OFW.

Statistical Analysis
Statistical analysis of corn grain yield response to OFW and N application and MERN calculated for different experiments was performed by the PROC GLM procedure of SAS (SAS Institute, 1996). The analysis of variance for the effect of N on corn crop yields and change in MERN due to OFW application was performed by dividing the data into three data subsets, representing the rate, time, and landscape position of OFW application. The Cate and Nelson approach (Cate and Nelson, 1987) was used to analyze the corn grain yield and preplant and PSNT soil NO3–N data to determine the critical level above which N application is considered ineffective.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Soil Nitrate Nitrogen at Preplant and Presidedress Time of Sampling
Average preplant and PSNT soil NO3–N content values for all experiments are given in Table 3. Soil NO3–N values were affected by the OFW management conditions at both sampling times. Soil NO3–N values at both sampling times decreased with increasing spring-applied OFW. Soil NO3–N were lowest for spring-applied OFW compared with control and fall-applied OFW. Soil inorganic N depletion during initial stages of decomposition of edible oils, fats, volatile fatty acids, and OFW has been reported (Smith, 1974; Higuchi and Kurihara, 1980; Kirchmann and Lundvall, 1993; Sorensen, 1998; Plante and Voroney, 1998; Rashid and Voroney, 2003). Soil NO3–N values in plots that received OFW in fall were also lower after its application but increased in the following spring. Soil N immobilized during the decomposition of OFW was apparently remineralized (Plante and Voroney, 1998; Rashid and Voroney, 2003) and became available to the growing corn crop (Rashid and Voroney, 2004).


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  		Table 3. Soil NO3–N at preplant and presidedress (PSNT) time of sampling for all locations (Elora Research Station and on-farm) during 1995, 1996, and 1997 (soil samples were taken from "0 N" plots and average of four replications is given).

 
Soil NO3–N contents at lower-slope positions were higher compared with upper slope and midslope positions during both years (Table 3). Higher amounts of preplant and PSNT soil NO3–N at the lower slope position might have been due to the fact that this position typically has high amounts of organic matter and total N (Gregorich and Anderson, 1985) and NO3–N (Rashid and Voroney, 2005) compared with soils in upper slope positions. The lower slope positions also receive N-rich topsoil from higher slope positions as a result of redistribution (Pennock et al., 1994).

Corn Grain Yield Response to Oily Food Waste and Nitrogen Fertilizer
Analysis of variance for the effect of OFW management treatments and N application on corn grain yield was performed by dividing the data in three subsets: (i) rate of OFW, (ii) time of OFW, and (iii) slope positions. Corn grain yields were significantly affected (P < 0.05) by OFW management and N application rate (Table 4). Corn grain yields were significantly decreased with increasing rate of OFW application. Soil NO3–N contents decreased with the increasing OFW application rate and were the lowest where OFW was applied at 20 Mg ha–1 (Table 3). When readily decomposable organic matter with a high C/N ratio is added to soil, the heterotrophic microorganisms become N-limited and soil inorganic N is immobilized during the decomposition of these materials (Jackson et al., 1989; Whitmore and Handayanto, 1997). Nitrogen immobilization during decomposition of edible oil and OFW were observed in laboratory (Plante and Voroney, 1998) and field studies (Rashid and Voroney, 2003). The extent of N immobilization also depends on the amount of OFW applied. A significantly higher net N immobilization was observed with the higher application rate of OFW compared with the low rate of OFW application (Plante and Voroney, 1998).


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  		Table 4. Effect of oily food waste and N application on corn grain yields for all experiments.

 
Corn grain yields were also affected by the time of OFW application and were significantly low in spring-applied OFW compared with fall-applied OFW. Corn grain yields under WWC treatment were significantly lower compared with control and fall-applied OFW and were significantly higher compared with spring-applied OFW. The yield difference between fall-applied OFW and spring-applied OFW could have been due to the difference in available N in soil under both treatments. The amount of available N in spring-applied OFW was low compared with fall-applied OFW (Table 3). Net immobilization was observed in plots receiving OFW in spring and net mineralization was observed in plots receiving OFW in fall (Rashid and Voroney, 2003).

Landscape positions within a field also affected the corn grain yields. Highest yields were recorded at lower slope positions followed by upper and midslope positions. Soil NO3–N at lower slope positions at preplant and PSNT were higher compared with upper and midslope positions during both years (Table 3). Lower slope positions typically have high amounts of organic matter and total N compared with soils in upper slope positions (Gregorich and Anderson, 1985) because they collect N-rich topsoil from surrounding slope positions as a result of redistribution (Pennock et al., 1994). Higher soil NO3–N contents at lower slope positions during both years might have accelerated the decomposition of applied OFW, which resulted in remineralization of immobilized N during its decomposition. Amount of soil-available N also affects the decomposition of applied waste materials, as N availability influences decomposition of organic materials (Recous et al., 1995; Mary et al., 1996). Recous et al. (1995) reported that rate of plant residue decomposition was higher where soil-available N levels were high compared with low soil-available N levels. Significantly higher corn grain yields at lower slope positions reveals that N availability and N demand of plants was well synchronized under these conditions.

Corn grain yields were also significantly affected by the rate of N application under all OFW management conditions. The average corn grain yields (average over all OFW rates and times of application) significantly increased with the application of 50, 100, and 150 kg N ha–1. However, the corn grain yields were not significantly increased when N was applied at 200 kg N ha–1. The trend of corn grain yield response to applied N at different landscape positions (Experiment 3) was different compared with Experiments 1 and 2. Corn grain yields (average over all slope positions) significantly increased with the application of 50 and 100 kg N ha–1 and leveled off beyond 100 kg N ha–1.

Maximum Economic Rates of Nitrogen
Quadratic response equations for all experiments used to calculate the MERN are presented in Table 5. Maximum economic rates of N application were calculated for each replication for all experiments for statistical analysis of the data. Maximum economic rates of N application were different for each OFW rate, time, and location of application and ranged between 0 to 182 kg ha–1 (Table 6). Analysis of variance for MERN for OFW rate, time, and location of application was performed separately. Maximum economic rate of N application values were significantly (P < 0.05) increased with the increasing rate of OFW application. Maximum economic rate of N application values were also significantly higher where OFW was applied in spring compared with fall-applied OFW, the control, and WWC. Supplemental fertilizer N (60 kg N ha–1) was required for plots receiving OFW in spring to maintain corn crop yields (Rashid and Voroney, 2004). Lower slope position had significantly lower MERN values compared with midslope and upper slope positions. No additional fertilizer N was required for corn production at the lower slope position where OFW was applied in spring (Rashid and Voroney, 2005). The variability in MERN can be attributed to the effect of OFW management conditions (rate, time, and field slope positions) on soil NO3–N content. The MERN values varied inversely with the amount of NO3–N in soil.


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  		Table 6. Maximum economic rate of N application (MERN) for all experimental locations during 1995, 1996, and 1997.

 
Correlations of Soil Nitrate-Nitrogen with Yield and Maximum Economic Rate of Nitrogen
The relationship between relative yield and soil NO3–N at preplant time of sampling and PSNT at the 0- to 30-cm depth is presented in Fig. 1 . The variability in relative yield was better explained by PSNT soil NO3–N content (R2 = 0.74) compared with preplant soil NO3–N contents (R2 = 0.55). The critical points at the 95% relative yield level for preplant and PSNT soil NO3–N contents were 18 and 21 mg kg–1, respectively. The critical value of 21 mg NO3–N kg–1 falls in the range of 20 to 30 mg NO3–N kg–1 soil reported for corn grown in different regions of North America (Blackmer et al., 1989; Fox et al., 1989; Magdoff, 1991; Binford et al., 1992; Roth et al., 1992; Klausner et al., 1993; Sims et al., 1995; Vyn et al., 1999).



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  		Fig. 1. Relationship between relative yield and (a) preplant and (b) PSNT soil NO3–N at the 0- to 30-cm depth (Cate and Nelson approach).

 
The relationship between MERN and preplant and PSNT soil NO3–N contents at the 0- to 30-cm depth is illustrated in Fig. 2 . The variability in MERN was better explained by PSNT soil NO3–N content (r2 = 0.88) compared with preplant soil NO3–N contents (r2 = 0.74). Nitrogen fertilizer recommendations can be made based on the linear relationship between MERN and PSNT soil NO3–N levels. Based on the regression model in Fig. 2b, N fertilizer recommendations for corn grown on fields amended with OFW in southern Ontario can be calculated by using the following equation:

[2]
where Y = N fertilizer kg ha–1, and x = PSNT soil NO3–N (0- to 30-cm depth).



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  		Fig. 2. Linear correlation between MERN and (a) preplant and (b) PSNT soil NO3–N at the 0- to 30-cm depth.

 

   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Soil NO3–N (0- to 30-cm depth) at preplant and PSNT were affected by the application of OFW and varied with the OFW management conditions. Soil NO3–N contents at PSNT were higher compared with samples taken at preplant soil sampling time under all OFW management conditions. Corn grain yields were also affected by OFW management conditions. Corn yield response to applied N fertilizer varied under different OFW management conditions. Maximum economic rate of N application varied depending on OFW management conditions. Soil NO3–N at PSNT had the higher correlation with MERN compared with soil NO3–N at preplant time of sampling. Post OFW application soil testing for NO3–N at PSNT is more appropriate for making N fertilizer recommendations for corn grown on soil amended with OFW in this geographical region.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 


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