JEQ Grow Your Career With ASA
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Related articles in JEQ
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (6)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Rashid, M. T.
Right arrow Articles by Voroney, R. P.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Rashid, M. T.
Right arrow Articles by Voroney, R. P.
Agricola
Right arrow Articles by Rashid, M. T.
Right arrow Articles by Voroney, R. P.
Related Collections
Right arrow Nitrogen
Right arrow Nutrient Cycling
Right arrow Water Pollution
Right arrow Industrial Waste
Published in J. Environ. Qual. 32:1881-1886 (2003).
© 2003 ASA, CSSA, SSSA
677 S. Segoe Rd., Madison, WI 53711 USA

TECHNICAL REPORTS

Waste Management

Recycling Soil Nitrate Nitrogen by Amending Agricultural Lands with Oily Food Waste

M. T. Rashid*,a and R. P. Voroneyb

a Institute of Natural Resources and Environmental Sciences, NARC, Park Road 45500, Islamabad, Pakistan
b University of Guelph, ON, Canada N1G 2W1

* Corresponding author (trashid256{at}yahoo.com).

Received for publication August 30, 2002.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
With current agricultural practices the amounts of fertilizer N applied are frequently more than the amounts removed by the crop. Excessive N application may result in short-term accumulation of nitrate nitrogen (NO3–N) in soil, which can easily be leached from the root zone and into the ground water. A management practice suggested for conserving accumulated NO3–N is the application of oily food waste (FOG; fat + oil + greases) to agricultural soils. A two-year field study (1995–1996 and 1996–1997) was conducted at Elora Research Center (43°38' N, 80° W; 346 m above mean sea level), University of Guelph, Ontario, Canada to determine the effect of FOG application in fall and spring on soil NO3–N contents and apparent N immobilization–mineralization of soil N in the 0- to 60-cm soil layer. The experiment was planned under a randomized complete block design with four replications. An unamended control and a reference treatment [winter wheat (Triticum aestivum L.) cover crop] were included in the experiment to compare the effects of fall and spring treatment of oily food waste on soil NO3–N contents and apparent N immobilization–mineralization. Oily food waste application at 10 Mg ha-1 in the fall decreased soil NO3–N by immobilization and conserved 47 to 56 kg NO3–N ha-1, which would otherwise be subject to leaching. Nitrogen immobilized due to FOG application in the fall was subsequently remineralized by the time of fertilizer N sidedress, whereas no net mineralization was observed in spring-amended plots at the same time.

Abbreviations: CC, unamended control • FFOG, fall-applied oily food waste • FOG, oily food waste (fat + oil + greases) • SFOG, spring-applied oily food waste • WWC, winter wheat cover crop incorporated in spring


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
WITH CURRENT AGRICULTURAL PRACTICES the amounts of fertilizer N applied are frequently more than are removed by the crop. This excessive application of N may result in the short-term accumulation of NO3–N in soil (Roth and Fox, 1990; Vanotti and Bundy, 1994), which can easily be leached from the root zone and into the ground water (Wedland et al., 1998). Thus, management strategies have been developed to reduce NO3–N leaching losses including growing winter cover crops (Francis et al., 1998), return of on-farm organic waste materials such as cereal straw (Nicholson et al., 1997), and application of off-farm organic waste materials (Aitken et al., 1998).

One of the management practices suggested to achieve this goal is application of oily food waste (FOG). In Ontario, the amount of FOG available for land application annually is 90000 Mg. Like crop residues, FOG is a rich source of readily decomposable C and is low in N (C to N ratio = 90), and it may be used to immobilize NO3–N during periods of the year (fall and early spring) when leaching losses are the highest. Nitrogen immobilization has been reported in controlled laboratory decomposition studies of oil, fats, volatile fatty acids, and FOG (Smith, 1974; Higuchi and Kurihara, 1980; Kirchmann and Lundvall, 1993; Sorensen, 1998; Plante and Voroney, 1998). However, information regarding the effect of FOG on soil available N under field conditions is not available. The objective of the study was to determine the effect of FOG application on soil NO3–N contents in soil, and its effect on N cycling–conservation through immobilization and consequent mineralization in soil.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
The physical and chemical analyses of the soils and chemical composition of FOG are presented in Tables 1 and 2, respectively. The experiment was set out under a randomized complete block design with four replications. Oily food waste (FOG) was applied at a rate of 10 Mg ha-1 equivalent to 0.5% of solids in a 2 x 106 kg ha-1 furrow slice, in the fall (3 October) and in the spring (25 April) during both years (1995–1996 and 1996–1997). The FOG application was immediately incorporated in soil within 1 to 2 h using a moldboard plow. A separate winter wheat cover crop (WWC) treatment was included as a reference to compare the effect of time of FOG application on soil NO3–N levels. The winter wheat (cv. Harus) cover was planted on the same day that FOG was applied in the fall (3 October) and was incorporated into the soil in the spring on the same day that FOG was applied (25 April) in both years. The total quantities of WWC fresh biomass (C to N ratio = 14) incorporated in soil in 1996 and 1997 were 1.48 and 1.26 Mg ha-1 dry wt., respectively. Four samples of the cover crop (1 m2) from each replication were taken in spring before incorporation in soil and oven-dried (60°C) to determine the quantity of cover crop residue retained. Three samples of FOG were taken at the application date for analyses of oil (Greenberg et al., 1995), total C contents (Tiessen and Moir, 1993), total N contents (McGill and Figueiredo, 1993), pH (Peech, 1965), and electrical conductivity (EC) (Bower and Wilcox, 1965). A corn (cv. Pioneer 3905) crop was planted on these amended plots in the spring during both years of experimentation.


View this table:
[in this window]
[in a new window]
  		Table 1. Selected physical and chemical properties of experimental sites (0–30 cm) at Elora Research Station in 1996 and 1997.

 

View this table:
[in this window]
[in a new window]
  		Table 2. Chemical properties of fall (FFOG)- and spring (SFOG)-applied oily food waste applied to experimental sites at Elora Research Station in 1996 and 1997.

 
Soil samples (5 cores plot-1, 4.5 x 10 m) were taken from 0 to 15, 15 to 30, and 30 to 60 cm weekly from plots not receiving N fertilizer application (0 N plots) from all treatments including unamended control (CC), winter wheat cover crop (WWC), fall-applied food waste (FFOG), and spring-applied food waste (SFOG). Soil sampling was started from the day when FFOG was applied in the fall (3 October) both during fall 1995 and 1996. Soil sampling continued until soil freeze-up and resumed in early spring (25 April) and continued to 4 July during 1996 and 1 August in 1997. Fall soil sampling was done from CC, WWC, and FFOG treatment plots. Spring–summer samplings included the CC, WWC, FFOG, and SFOG treatments in which corn plants were growing. Soil sampling from SFOG was also started on the same day when FOG was applied in the spring (25 April).

Soil samples were brought to the lab immediately and stored at -8°C. Samples were sieved moist through a 2-mm sieve and extracted with 2 M KCl to determine soil NO3–N (Keeney and Nelson, 1982). Apparent N immobilization or mineralization was calculated by subtracting the NO3–N content of CC plots (0 N) from that of the FOG-amended and WWC (0 N) plots.

Statistical analyses of soil NO3–N contents and apparent N immobilization (repeated measures analysis) data were performed by the Proc Glm procedure in SAS (SAS Institute, 1990). The analysis of variance for the change in soil NO3–N (0–60 cm) and apparent N immobilization due to FOG and WWC management treatments was performed by dividing the data into two data subsets in 1995–1996 and 1996–1997, representing fall and spring–summer sampling. Spring–summer sampling periods were further divided into two in 1996 and three sampling times in 1997, to compare the FOG management treatment means and slopes of the trend lines within a particular sampling period.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Soil Nitrate Nitrogen during Fall and Spring–Summer
Soil NO3–N contents were significantly affected by FOG management treatments. The effect of FOG management on soil NO3–N contents in fall 1995 and spring–summer 1996 is presented in Fig. 1 . Soil NO3–N contents (0- to 60-cm soil layer) decreased from 79 to 8 kg ha-1 one week after FFOG application in fall 1995. Soil NO3–N contents during 10–24 October were significantly lower in FFOG compared with WWC and CC treatment plots (Table 3); however, the soil NO3–N contents were similar (P < 0.05) in WWC and CC treatments. A significant temporal decrease in soil NO3–N was also observed in all treatments. The extent of decrease in NO3–N over time (slopes of lines were significantly different) was much higher in FOG-amended plots compared with CC and WWC. A similar (P < 0.05) trend of a temporal decrease in NO3–N content was observed in WWC and CC.



View larger version (36K):
[in this window]
[in a new window]
  		Fig. 1. Soil NO3–N contents as affected by oily food waste (FOG) management during fall 1995, spring–summer 1996, fall 1996, and spring–summer 1997.

 

View this table:
[in this window]
[in a new window]
  		Table 3. Effect of oily food waste (FOG) management on soil NO3–N contents and slope of trend lines for selected time periods{dagger} during fall 1995, spring–summer 1996, fall 1996, and spring–summer 1997.

 
Soil NO3–N contents decreased from 43 to 9 kg ha-1 one week after SFOG application. The SFOG-amended plots had the lowest soil NO3–N and were significantly lower than those with the WWC, FFOG, and CC treatments in spring 1996 (2–30 May). A comparison of slopes of the trend lines (Table 3) shows that the temporal increase in soil NO3–N content in FFOG plots was similar to that observed for the CC treatment in spring 1996. However, the temporal increase in soil NO3–N content was significantly lower in WWC and SFOG compared with FFOG and CC plots.

Average soil NO3–N contents in FFOG-amended plots were similar to those observed in CC in summer 1996 (13 June–4 July). The average soil NO3–N contents observed in WWC and SFOG during this sampling period were significantly lower compared with those observed in FFOG and CC plots. Although the relative temporal increase in soil NO3–N in SFOG plots was similar to that observed in the FFOG plots (similar slopes of the trend lines), the average soil NO3–N contents were significantly lower compared with the FFOG plots.

The effect of FOG management on soil NO3–N contents in fall 1996 and spring–summer 1997 is presented in Fig. 1. Soil NO3–N contents (0- to 60-cm soil layer) decreased from 57 to 7 kg ha-1 one week after of FFOG application in fall 1996. Soil NO3–N contents after FFOG (10 October–7 November) were significantly lower as compared with WWC and CC plots (Table 3). A significant temporal increase in soil NO3–N content was observed during the next five weeks with the FFOG treatment; however, a temporal decrease in soil NO3–N contents was observed with the WWC and CC treatments. Although the rate of temporal decrease in soil NO3–N content was similar with the WWC and CC treatments, the average soil NO3–N contents in WWC were significantly lower compared with CC.

Soil NO3–N contents decreased from 42 to 7 kg ha-1 one week after SFOG application in spring 1997. The SFOG-amended plots had low soil NO3–N contents and were significantly lower compared with WWC, FFOG, and CC treatments during the spring (2 May–13 June). A comparison of linear line slopes (Table 3) shows that the temporal increase in soil NO3–N was similar in SFOG, WWC, and CC. However, the temporal increase in soil NO3–N in these treatments was significantly lower compared with that observed with the FFOG treatment.

Soil NO3–N contents with the FFOG treatment were similar to those observed with the CC treatment during summer 1997 (20 June–11 July) and were significantly higher compared with those observed with the WWC and SFOG treatments. Although the relative temporal increases in soil NO3–N contents in the SFOG- and FFOG-amended plots were similar (similar trend line slopes), the average soil NO3–N content with SFOG was significantly lower compared with those observed with FFOG during this sampling period.

A significant decrease in soil NO3–N content was observed in all treatments after 11 July 1997. The relative rate of decrease in soil NO3–N content was significantly lower in SFOG-amended plots compared with CC, WWC, and FFOG plots. Average soil NO3–N content was significantly lower in the WWC compared with CC and FFOG plots; however, the extent of decrease in soil NO3–N content was similar with all treatments during the 11 July to 1 August soil sampling period.

Incorporation of organic materials in soil causes a rapid increase in the soil microbial biomass (Fauci and Dick, 1994; Jensen, 1997), which acts as a sink and source for plant nutrients and is an active participant in nutrient cycling (McGill et al., 1986). Microbial C and N metabolism in soil are closely linked since, after adding C to soil, substrates generated by heterotrophic metabolism are utilized to increase the microbial biomass and hence increase the N demand of decomposer populations (Ladd and Foster, 1988). Rapid depletion of soil inorganic N during the initial stages of decomposition of FOG has previously been reported by Plante and Voroney (1998). Similar results have been reported previously during the decomposition of nonleguminous plant materials (Powlson et al., 1985; Ocio et al., 1991; Mary et al., 1996).

Soil NO3–N contents increase in spring under all management treatments and a peak was observed in May until the time of N sidedress (27 June) during both years. This trend of increasing soil NO3–N is attributed to the release of N when soil moisture and temperature promote soil microbial activity. Nitrogen mineralization is greatly influenced by soil moisture and temperature and their interactive effects (Goncalves and Carlyle, 1994; Sierra, 1997; Walse et al., 1998). Goncalves and Carlyle (1994) have shown that N mineralization was a linear function of time. The difference between the first and last samplings after the application of FFOG and SFOG showed that soil NO3–N increased under FFOG (nine- and sixfold) and SFOG-amended (three- and fourfold) plots during 1995–1996 and 1996–1997, respectively.

The NO3–N contents under WWC during spring 1996 were lower compared with spring 1997. The low amount of NO3–N in this treatment during spring 1996 was not expected, as an addition of low C to N ratio (14) crop residues generally does not cause soil N to be immobilized. However, this reduction in soil NO3–N content may be attributed to denitrification as total rainfall received in spring 1996 (April, May, and June) was higher (293 mm) compared with that in spring 1997 (169 mm) for the same period. High soil water content in the presence of readily degradable C substrate and NO3–N provide conditions favorable for denitrification (Tiedje, 1988). An increase in denitrification due to an increase in soil water content has been reported previously (Aulakh et al., 1991; Weier et al., 1993; Tenuta and Beauchamp, 1995).

Apparent Nitrogen Immobilization during Fall and Spring–Summer
Apparent N immobilization was significantly affected by FOG management treatments. The effects of FOG management on apparent N immobilization during fall 1995 and spring–summer 1996 are presented in Fig. 2 . One week after FFOG application (10 October), 56 kg NO3–N ha-1 was immobilized whereas the average amounts of immobilized N by the FFOG during the next three weeks (10–24 October) was 49 kg NO3–N ha-1 (Table 4).



View larger version (32K):
[in this window]
[in a new window]
  		Fig. 2. Apparent N immobilization due to oily food waste (FOG) management during fall 1995, spring–summer 1996, fall 1996, and spring–summer 1997.

 

View this table:
[in this window]
[in a new window]
  		Table 4. Effect of oily food waste (FOG) management on apparent N immobilization and slope of trend lines for selected time periods{dagger} during fall 1995, spring–summer 1996, fall 1996, and spring–summer 1997.

 
The SFOG application immobilized significantly higher amounts of soil N (44 kg NO3–N ha-1) compared with the FFOG and WWC treatments (21 and 28 kg NO3–N ha-1, respectively) during spring 1996 (2–30 May). A temporal increase in apparent N immobilization was observed in the SFOG and WWC plots; however, a decreasing trend in N immobilization was observed in the FFOG plots. A higher temporal decrease in apparent N immobilization was observed in FFOG plots compared with WWC and SFOG during summer 1996 (13 June–4 July). At the time of N fertilizer sidedress (27 June) apparent net mineralization was observed in the FFOG plots, whereas N immobilization was still occurring in the WWC and SFOG plots.

Apparent N immobilization was also significantly affected by FOG management treatments during fall 1996 and spring–summer 1997 (Fig. 2). One week after FFOG application (10 October), 47 kg NO3–N ha-1 was immobilized and a temporal decrease in apparent N immobilization was observed in FFOG-amended plots during the next five weeks (10 October–7 November). The average amount of immobilized N by FFOG during this sampling period was 36 NO3–N ha-1 (Table 4).

The SFOG application immobilized significantly higher amounts of soil N (33 kg NO3–N ha-1) compared with FFOG and WWC (9 and 3 kg NO3–N ha-1, respectively) during spring 1997 (2 May–13 June). A temporal decrease in apparent N immobilization was observed in all treatments during this sampling period. A higher temporal decrease in apparent N immobilization was observed in the FFOG and SFOG plots compared with WWC treatment during summer 1997 (20 June–1 August). Apparent net mineralization was observed in the FFOG plots at the time of N fertilizer sidedress (27 June), whereas in the WWC and SFOG plots N immobilization still prevailed.

According to the mineralization and immobilization turnover (MIT) hypothesis of N in soil, the microbial biomass obtains some of the N needed for synthetic reactions associated with growth and metabolism from the soil inorganic N pool (Jansson and Persson, 1982). The rapid decrease in soil NO3–N observed after the FFOG application is due to N immobilization by soil microorganisms during decomposition of FOG. Maximum N immobilization was evident in the first week after FFOG application. Plante and Voroney (1998) have shown in a laboratory study that the peak level of immobilization coincided with the peak in microbial biomass. A temporal decrease in N immobilization was observed and N mineralization occurred in FFOG-treated plots at the time of N fertilizer sidedress (27 June) during both years.

The pattern of N immobilization followed by mineralization observed in the field is consistent with that reported in laboratory studies involving cooking oils (Smith, 1974), oils and fats of plant and animal origin (Higuchi and Kurihara, 1980), volatile fatty acids (Kirchmann and Lundvall, 1993; Sorensen, 1998), and FOG (Plante and Voroney, 1998). Dominance of N immobilization after FFOG application during fall and winter 1995 and 1996 and spring 1996 and 1997 provided an opportunity for reducing the potential for NO3–N leaching during periods of high leaching potential. These results suggest that 36 to 49 kg NO3–N ha-1 was conserved due to application of FFOG. Prevalence of apparent N mineralization at the time of N fertilizer sidedress (27 June) indicated that FOG decomposition was essentially complete. If soil FOG had remained in spring (as a result of a late fall application of FOG), immobilization would have occurred that might have adversely affected the following crop.

Application of FOG in spring immobilized 44 and 33 kg NO3–N ha-1 after one week. Although apparent N immobilization decreased over time, it remained higher in the SFOG compared with the WWC and FFOG treatments throughout the spring–summer sampling period during both years. However, the effect of this trend of apparent N immobilization due to SFOG application was observed in terms of higher maximum economic rate of nitrogen application (MERN) and lower maximum economic yield (MEY) values in SFOG-amended plots both in 1996 and 1997 compared with FFOG plots. Supplemental N was required to maintain corn grain yields in SFOG-amended plots (results presented in a separate paper).

Maximum Apparent Nitrogen Immobilization
The maximum amounts of N immobilized by FFOG and SFOG treatments are presented in Table 5. Statistical analysis of the data showed that higher amounts of N were immobilized by both FOG management treatments during 1996 compared with 1997. The average amount of immobilized N due to FFOG (51 kg NO3–N ha-1) was significantly higher (P < 0.05) compared with SFOG (42 kg NO3–N ha-1). The maximum amounts of N immobilization due to FFOG and SFOG (6.4 and 5.3 kg N Mg-1 FOG C, that is, 51 and 42 kg N ha-1) in 1996 and 1997 are lower compared with those reported for wheat straw, 10 kg N Mg-1 (Addiscott and Dexter, 1994) and those reported for maize, 11 kg N Mg-1 maize residue (Green and Blackmer, 1995). The N present in FOG may be supplying some of the N requirements for its decomposition.


View this table:
[in this window]
[in a new window]
  		Table 5. Maximum amount of N immobilized due to application of fall (FFOG)- and spring (SFOG)-applied oily food waste in 1995–1996 and 1996–1997.

 

   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
In this study oily food waste application at 10 Mg ha-1 in the fall decreased soil NO3–N by immobilization and conserved 47 to 56 kg NO3–N ha-1, which would otherwise be subject to leaching. Nitrogen immobilized was subsequently remineralized. This mineralized N in spring was available for crop plant growth by the time of fertilizer N sidedress, whereas no net mineralization was observed in SFOG-amended plots at the same time. It is recommended that FOG should be applied annually in early fall to provide sufficient time for its decomposition in soil at a rate of 6 kg NO3–N immobilized Mg-1 FOG C to immobilize all residual soil NO3–N, and to avoid the deleterious effects of N immobilization on crop growth in spring. There is a need for research on the long-term effects of FOG amendment on the soil as there is potential for increased NO3–N leaching over the following winter, which must be managed.


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


Related articles in JEQ:

This Issue in Journal of Environmental Quality

JEQ 2003 32: 1577-1582. [Full Text]  



This article has been cited by other articles:


Home page
 J. Environ. Qual.Home page
M. T. Rashid and R. P. Voroney
Nitrogen Fertilizer Recommendations for Corn Grown on Soils Amended with Oily Food Waste
J. Environ. Qual., October 12, 2005; 34(6): 2045 - 2051.
[Abstract] [Full Text] [PDF]

Home page
 Soil Sci.Home page
M. T. Rashid and R. P. Voroney
Predicting Nitrogen Requirements for Corn Grown on Soils Amended with Oily Food Waste
Soil Sci. Soc. Am. J., June 28, 2005; 69(4): 1256 - 1265.
[Abstract] [Full Text] [PDF]

Home page
 J. Environ. Qual.Home page
M. T. Rashid and R. P. Voroney
Field-Scale Application of Oily Food Waste and Nitrogen Fertilizer Requirements of Corn at Different Landscape Positions
J. Environ. Qual., April 20, 2005; 34(3): 963 - 969.
[Abstract] [Full Text] [PDF]

Home page
 Agron. J.Home page
M. T. Rashid and R. P. Voroney
Land Application of Oily Food Waste and Corn Production on Amended Soils
Agron. J., July 1, 2004; 96(4): 997 - 1004.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Related articles in JEQ
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (6)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Rashid, M. T.
Right arrow Articles by Voroney, R. P.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Rashid, M. T.
Right arrow Articles by Voroney, R. P.
Agricola
Right arrow Articles by Rashid, M. T.
Right arrow Articles by Voroney, R. P.
Related Collections
Right arrow Nitrogen
Right arrow Nutrient Cycling
Right arrow Water Pollution
Right arrow Industrial Waste

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Agronomy Journal Crop Science
Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
Soil Science Society of America Journal Journal of Plant Registrations The Plant Genome