Published in Agron. J. 96:1344-1348 (2004).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Paper
Application of Wood Ash to Acidic Boralf Soils and its Effect on Oilseed Quality of Canola
S. J. Pattersona,
S. N. Acharyab,
A. B. Bertschic and
J. E. Thomasa,*
a Dep. of Biol. Sci., Univ. of Lethbridge, Lethbridge, AB T1K 3M4, Canada
b Agric. and Agri-Food Canada, Lethbridge Res. Cent., P.O. Box 3000, Lethbridge, AB T1J 4B1, Canada
c Alberta-Pacific Forest Industries, Inc., Boyle, AB T0A 0M0, Canada
* Corresponding author (thomas{at}uleth.ca)
Received for publication July 21, 2003.
 |
ABSTRACT
|
|---|
Acidic Typic Cryoboralf soils amended with wood ash can raise soil pH and can supplement plant growth by adding minerals and micronutrients. However, presence of other elements in soils such as Cd, S, and Zn can affect plant growth and seed quality. In an earlier paper, we have shown that wood ash applications on Typic Cryoboralf and Typic Cryocrept soils in Alberta, Canada, increased canola (Brassica rapa L.) yield by 72%. In this study, the effect of a single application of 0, 6, 12.5, and 25 t ha–1 (dry weight) wood ash on oilseed quality, based on oil, protein, chlorophyll, and glucosinolate content, was examined over three growing seasons from 1998 to 2000. Seed oil and protein content of ash-treated plots either increased or remained the same as controls. In contrast, significant increases (p < 0.05) in tissue concentrations of S and seed oil glucosinolates were observed in ash-amended plots. While these changes remained within acceptable limits for canola, seed oil and tissue quality were lower than the average level found in Canada no. 1 grade canola. During the 3-yr period, average Zn content of the oilseed was not different from control plots (P > 0.05). Levels of B in ash-treated soils were different from each other but not from the controls (P < 0.05). Cadmium levels were below detection limits for the instrumentation used (0.08 mg kg–1). These results indicate that use of wood ash on acidic soils has the potential to increase seed oil content but may adversely affect quality of the oilseed produced.
|
INTRODUCTION
|
|---|
AGRICULTURAL LANDS developed within or abutting the boreal forest of Alberta, Canada, contain acidic Typic Cryoboralf and Typic Cryocrept soils with limited productivity. These soils have developed primarily under forest vegetation and are slightly to strongly acidic with low nutrient contents requiring additional fertilizer inputs to maintain productivity (Canadian Dep. of Agric., 1972). Of the 6 million ha of acidic soils in Western Canada with a pH of less than 6.5, 90% occur in Alberta (Lickacz, 2002). In Alberta, approximately 180000 t of wood ash is produced on an annual basis and until recently have been disposed of through landfilling (Lickacz, 2002).
Wood ash has drawn the attention of the agricultural community as a liming agent, but it also contains macronutrients, micronutrients, and trace elements, some of which are essential for plant growth but can also affect crop quality (Vance, 1996; Muse and Mitchell, 1995; Meyers and Kopecky, 1998). For example, brassicaceous crops like canola require S for amino acid and protein synthesis. Sulfur is also used for the synthesis of glucosinolates in canola, which lowers oilseed quality when present in high proportions (Rosa et al., 1997). Oil, protein, and glucosinolate content of canola can be affected by S fertilization (Haneklaus et al., 1999). Minimum levels of S are required to support N utilization and protein synthesis in oilseeds while increased S fertilization rates are known to result in higher levels of seed oil and glucosinolates (Nuttal et al., 1987). Haneklaus et al. (1999) suggested that application of 25 kg S ha–1 is adequate to keep depleted soils above the critical nutrient threshold required by oilseeds for growth and that S fertilization of 40 kg ha–1 is sufficient to satisfy demands of a high-yielding crop. Wood ash also contains trace elements like B, Cd, and Zn, which if allowed to accumulate in the soil can become phytotoxic to plants. More importantly, high levels of Cd and Zn in plants pose a health risk to both animals and humans who consume the plants or plant products (Natl. Res. Counc., 1980).
We have shown that supplementation of Typic Cryoboralf soils with wood ash resulted in an average increase in canola yield of 72% from 1998 to 2000 (Patterson et al., 2004). However, economic benefit of this increase may be affected by oilseed quality; i.e., oil, protein, glucosinolate, and chlorophyll content of the oilseeds. The purpose of this study was to evaluate the effect of wood ash additions on canola oilseed quality, including accumulation of heavy metals in the seed.
|
MATERIALS AND METHODS
|
|---|
Study Site
The field trial site was located 200 km northeast of Edmonton, AB, at 54°55' latitude and 112°52' longitude. The Athabasca region of the boreal forest within Alberta, Canada, normally receives about 503 mm of total precipitation annually based on a 30-yr average from 1971 to 2000 (Environment Canada, 2002). Approximately 60% of the total precipitation occurs from May to August, and during the 3-yr period of this study (1998, 1999, and 2000), the amount of precipitation was 32, 15, and 24% lower than the long-term average, respectively, for this area (Environment Canada, personal communication, 2002). Temperatures during the study period were similar to the 30-yr average for the area. Annual mean temperatures were 2.6, 3.0, and 4.0°C for the region. The mean growing season temperatures from June to September were 14.5, 14.2, and 15.2°C, respectively, for 1998, 1999, and 2000 (Environment Canada, personal communication, 2002).
The study site was gently undulating with 2 to 4% slopes and consisted of clay loam soils (average bulk density of 1.2 g cm–3); selected soil properties are presented in Table 1. The site was composed of 10% Typic Cryocrept and nearly 90% Typic Cryoboralf soils (Canadian Dep. of Agric., 1972). The loam-textured soil was well drained and had developed under forest cover with a strong to slightly acidic pH of 
5 to 6.5 over alluvial lacustrine deposits (Canadian Dep. of Agric., 1972). The land was under continuous hay production prior (>4yr) to this study. Both soils are considered low in nutrient content and required additional fertilizer inputs for optimum crop production.
The land selected for the field study was divided into three replicates; one replicate was located in the northeast, one in the northwest, and one in the southeast portions of a quarter section (SE1/4 22-68-19W4) of land. Plot dimensions in the northwest and southeast replicates were 50 by 100 m long while plots in the northeast replicate were 30 by 100 m.
Wood Ash
A pulp and paper mill located near the study site produced approximately 16000 t of wood ash annually through the incineration of wood waste (wood, bark, knots, and low quality chips) also called hog fuel. This hog fuel was composed of both softwood (Picea and Pinus) and hardwood (Populus) species. Chemical properties of the ash produced were characterized by determining available nutrients, total nutrients, available metals, and total metals by EnviroTest Laboratories (Calgary, AB) using methods outlined by Carter (1993). Results of selected analyses are summarized in Table 2.
View this table:
[in this window]
[in a new window]
|
Table 2. Characteristics of wood ash used in this study and in other research involving application of wood ash to soil.
|
|
Experimental Design
Soil mixtures of 0.25, 0.50, and 1.00% wood ash in the top 0.2 m were achieved by applying wood ash on a dry weight basis at rates of 6, 12.5, and 25 t ha–1. Wood ash supplied for the study was stockpiled at the research site from March 1998 to mid-May 1998. Treatments were randomly assigned to each plot and wood ash applied in a single application starting mid-May 1998; no other supplemental ash applications were made. Wood ash was applied using a side discharge GEHL Scavenger Manure Spreader (Model 1330, GEHL Co., West Bend, WI) and was completed during the first week of June. Three passes of a breaking disc were used to incorporate the ash to a depth of 0.2 m, and then the ash was allowed to incubate for 5 d before first-year seeding. Treatments in the study were separated by a 3-m buffer zone that was roto-tilled bimonthly to a depth of 0.2 m to minimize weed growth.
No supplemental P or K fertilizer was applied to the study plots. Only N fertilizer was applied during the 3-yr period of the field study. Samples from the top 0.2 m of the field site were collected and analyzed for available soil N (Mulvaney, 1996). Urea (46–0–0) was applied to each plot at rates of 56, 103, and 108 kg ha–1 actual N in 1998, 1999, and 2000, respectively, to provide 130 kg N ha–1 (Canola Council of Canada, 2001).
Weeds in the canola plots were controlled each year using the pre-emergent granular herbicide Edge {ethalfluralin [N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine]; 1.25 kg a.i. ha–1} and by spraying Lontrel 360 [clopyralid (3,6-dichloro-2-pyridinecarboxylic acid); 100 g a.i. ha–1] with Poast Ultra (sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}; 144 g a.i. ha–1) and Merge (0.5% v/v) in early July. Due to late maturity, a preharvest application of Roundup {glyphosate [N-(phosphonomethyl)glycine]; 880 g a.i. ha–1} was used in early September 1998 to desiccate the crops.
A Polish canola cultivar, Maverick, was chosen for the study because of its early maturity. A Valmar Airflo Seeder (Model 1255, Valmar Airflo, Elie, MB, Canada) was used to seed plots perpendicular to wood ash treatments at a rate of 7.8 kg ha–1; canola seed was harvested using a Wintersteiger Nurserymaster Elite combine (Wintersteiger, Salt Lake City, UT).
Sample Analysis
Multiple seed samples (four per replication) were harvested from 9-m2 (1.5 by 6 m) plots. Seed samples were dried at 55°C for 3 d, cleaned using an Almaco Seed Cleaner (Allan Machine Co., Nevada, IA), and weighed to determine yield. Samples were analyzed by EnviroTest Laboratories (Calgary, AB) using the methods outlined by Carter (1993). Seed samples were digested using a modified USEPA 3050 consisting of a nitric and hydrochloric acid digestion to dissolve the metals (B, S, Cd, and Zn) followed by hydrogen peroxide to break down any organics. Analysis of the digest was done by inductively coupled plasma–atomic emission spectroscopy (ICP-AES). Further analysis for Cd found in oilseed samples of control (0) and 25 t ha–1 ash treatments also was done at a lower detection limit using an USEPA 3051 digestion, followed by analysis with ICP-mass spectroscopy (MS) at a detection limit of 0.08 mg kg–1. Nitrogen analysis of the samples was conducted by Kjeldahl digestion, using a Technicon Autoanalyzer (Technicon Instruments Corp., Tarrytown, NY) to provide total N within the sample (NAQUADAT no. 07021).
Oilseed quality analysis was performed by the Canadian Grain Commission's Grain Research Laboratory (Winnipeg, MB) on samples from control and ash-amended plots containing N fertilizer. Two subsamples per treatment for each of the 3 yr were analyzed for oil, chlorophyll, and glucosinolate content by near infrared spectroscopy (NIR) while protein content was determined by a Dumas (combustion) technique using a LECO FP-428 Nitrogen Determinator (Canadian Grain Commission, 2001). Results for oil, chlorophyll, and glucosinolate content were expressed on an 8.5% moisture basis.
Statistical Analysis
The experimental plots were laid out using a randomized complete block design with three replications. Each year, subsamples of seed were sent to determine oilseed quality (two subsamples per replication for oil, protein, glucosinolate, and chlorophyll) and macronutrient (one per rep for S) and micronutrient (four per rep for B and Zn) content. Results from oilseed quality and elemental analyses were subjected to an analysis of variance using SAS PROC MIXED (SAS Inst., 2001). The model used for ANOVA is presented in Table 3 where data were analyzed using year as repeated observation. When F was significant, statistical differences among the means were determined using a Fisher's Protected LSD test (
= 0.05).
View this table:
[in this window]
[in a new window]
|
Table 3. Significant F values for ‘Maverick’ canola seed oil, protein, glucosinolate, chlorophyll, S, B, and Zn as determined by ANOVA of samples collected in 1998, 1999, and 2000 from plots treated with a one-time application of 0, 6, 12.5, and 25 t ha–1 wood ash, plus an annual N supplement.
|
|
|
RESULTS AND DISCUSSION
|
|---|
Oil, protein, glucosinolate, chlorophyll, S, B, and Zn content within oilseeds were affected by year while addition of wood ash to the soil affected glucosinolate, S, and B content of the oilseed (Table 3). Throughout the study, oil and protein contents of the Polish canola Maverick grown on wood-ash–supplemented soils were higher than mean values published for the western Canada harvest survey for Canada no. 1 canola (Table 4). Our study shows that addition of 6 to 25 t ha–1 of wood ash to the test plots resulted in an average increase in seed oil content of 5.4% in the first year. This corroborates earlier observations made by Ahmad and Abdin (2000), who used different combinations of S and N to promote growth of another canola variety, Brassica compestris L. Wood ash used in this study contained 1.7% SO4 (Table 2) and increased S content in the soil by 25 to 90 mg kg–1 (Table 1) when 6 to 25 t ha–1 of wood ash was added to the soil. In 1998, oil content was significantly higher than that seen in other years (Table 4), and the samples collected from wood-ash–amended plots had a higher oil content than samples grown in the absence of ash. In 1999 and in 2000, little or no difference in oil content of seeds was observed between ash-supplemented and untreated plots even though the total yield of oilseed produced was higher than controls in all treatments (Patterson et al., 2004).
View this table:
[in this window]
[in a new window]
|
Table 4. Average oil, protein, glucosinolate, chlorophyll, and S content of ‘Maverick’ canola samples collected from plots treated with a one-time application of 0, 6, 12.5, and 25 t ha–1 wood ash, plus an annual N supplement in 1998, 1999, and 2000.
|
|
Protein and glucosinolate content of the seed oil was significantly higher in 1999 than in either 1998 or 2000. Glucosinolates are secondary metabolites that accumulate within oilseeds and at high concentrations can restrict use of the seed for animal feed (meal) after oil extraction even if the seeds contain high levels of protein (Iqbal et al., 1995; McClellan et al., 1993). In our study, elevated levels of S were found in the canola seed as well as an increase in glucosinolate content (Table 4). Although levels of glucosinolate in wood-ash–treated oilseed exceeded the levels for Canada no. 1 seed throughout the study, glucosinolate contents for all of the analyzed samples were below the allowable limit of 30 µmol g–1 of aliphatic glucosinolates (McCurdy, 1990) defined under Canadian regulations for canola. Glucosinolate levels for control oilseed produced in the absence of wood ash also were greater than average Canada survey values for Canada no. 1 grade canola in 2 out of 3 yr during the study (Table 4).
In 1998, chlorophyll levels were significantly lower than the other 2 yr, and the samples from both control and ash-treated plots were below the average level found in Canada no. 1 canola in the Canada harvest survey (Table 4). Due to late maturity, a preharvest application of Roundup was used in early September 1998 to desiccate the crop; use of desiccants to increase levels of mature seed at harvest is a normal practice in areas with short growing season. In 1999 and 2000, chlorophyll levels for most ash-treated oilseed exceeded the average level found in Canada no. 1 canola in the Canada harvest survey. A significantly higher chlorophyll content was observed in the last 2 yr of the study compared with the first year. Increases in seed oil chlorophyll content likely resulted from a high proportion of immature (green) seeds at the time of harvest (Canadian Grain Commission, 2001). The limited growing season of central Alberta and no application of desiccant before combining the seed during the last years may have been responsible for such an increase in chlorophyll content.
Years had a significant effect on oil, protein, glucosinolate, chlorophyll, and S contents of the oilseed samples, indicating that the environment was as important as wood ash treatment in determining seed and oil quality (Table 3). Grant and Bailey (1993) have shown that low soil moisture can result in low seed oil content and that low temperatures can result in delayed plant maturity, high oil content, and low protein. In contrast, high temperatures hasten onset of seed maturity and increase protein content of the seed while lowering oil content. Chlorophyll content in canola also can be affected by environmental stresses caused by extremes in air temperature and moisture conditions. Climate data from the study area, obtained from Environment Canada, indicated that temperature was above the 30-yr average for 1998 and 1999 but below average in 2000. The total precipitation during this time period was less than the 30-yr average for all 3 yr. Fluctuating weather conditions observed during the 3-yr study period may explain the yearly variation in canola quality observed during this study. However, continuous rotation of canola onto the same plots over the 3-yr study period also may have affected oilseed quality and yield.
Effect of Wood Ash on Oilseed Mineral Content
Wood ash treatment, year, and treatment x year interactions had a significant effect on S content of the oilseed while only wood ash treatment had a significant effect on B content of the oilseed (Table 3). Wood ash used in our study contained 1.7% SO4 (Table 2); this represents addition of 102, 213, and 426 kg S ha–1 when applying 6, 12.5, and 25 t ha–1 of wood ash, respectively, to the field plots. All wood ash applications resulted in a significant increase in S content of canola samples during the last 2 yr of the study (Table 4). In the first year (1998) of the study, only the S content for oilseed samples from the 6 and 25 t ha–1 ash applications were significantly greater than control values (Table 4).
Chlorophyll content in plants can be influenced by an increase in supply of B and/or Zn (Grewal et al., 1998). High levels of these micronutrients can negatively affect seed oil quality, leading to green or brown coloration and spoiling and causing difficulty in the hydrogenation process (Canadian Grain Commission, 2001). Zinc is important in the formation of chlorophyll and other plant enzymes (Salisbury and Ross, 1992). While increased supplementation of fields with wood ash resulted in a marginal nonsignificant increase (P > 0.05) in Zn concentrations in oilseeds (Table 5), changes in chlorophyll content did not appear to be related to Zn concentrations. During seed maturation, chlorophyll is metabolized so that fully ripe seeds contain little chlorophyll (Canadian Grain Commission, 2001). Thus, maturity of the oilseed at time of harvest likely contributed to the variation in chlorophyll content observed during the 3 yr of our study. Boron content of the oilseed was significantly higher in oilseed samples collected from 25 t ha–1 than those collected from 6 or 12.5 t ha–1 treatments (Table 5). However, the 25 t ha–1 treatment was not significantly different from the control.
View this table:
[in this window]
[in a new window]
|
Table 5. Average concentration of B and Zn in ‘Maverick’ canola oilseed (1998–2000) from plots supplemented with a one-time application of 0, 6, 12.5, and 25 t ha–1 wood ash, plus an annual N supplement.
|
|
Cadmium is a heavy metal that is naturally present in soils (Grant et al., 1998). Cadmium is not required for growth, but it can accumulate in plants, causing adverse effects on growth and, if consumed by animals, can bioaccumulate to toxic levels. Oilseed limits for Cd of 0.1 mg kg–1 have been suggested by the World Health Organization (WHO) for trade on international markets (Grant et al., 1998). In the present study, Cd levels in oilseed samples were below 0.08 mg kg–1 for control (no ash treatment) and 25 t ha–1 wood-ash–supplemented plots. These values were below levels of detection for the instrumentation used and so did not warrant further analysis.
|
CONCLUSIONS
|
|---|
Wood ash is an important by-product of the pulp and paper industry and has potential as a valuable soil supplement. However, quality of some crops, such as canola, may be influenced by its use. The present study shows that seed oil and protein content of ash-treated plots either increased or remained the same as controls over the 3 yr. In contrast, significant increases in tissue concentrations of S and seed oil glucosinolates were observed in ash-amended plots over all 3 yr. While these changes remained within acceptable limits for canola, the tissue quality was lower than the average level found in Canada no. 1 canola in the Canada harvest survey. Supplementation of acidic soils with wood ash can increase oilseed productivity but may decrease quality of the seed produced. This may be of concern to some producers growing this crop, in particular for those wishing to access export markets or using the oilseed meal for animal feed. However, before any substantial conclusions can be drawn, further studies should be conducted with different oilseed crops and cultivars to address the impacts of wood ash on oilseed quality.
|
ACKNOWLEDGMENTS
|
|---|
This research project was funded by Alberta–Pacific Forest Industries, Inc., and through NSERC in the form of an Industrial Postgraduate Scholarship awarded to the first author. We would also like to thank Alberta Environment, EnviroTest Laboratories, and Gateway Research Organization for their contributions to the study; the team members at Alberta–Pacific and numerous others who contributed throughout the study period; and Dr. R. Weselake for reading and commenting on the manuscript.
|
REFERENCES
|
|---|
- Ahmad, A., and M.Z. Abdin. 2000. Interactive effect of sulphur and nitrogen on the oil and protein contents and on the fatty acid profiles of oil in the seeds of rapeseed (Brassica campestris L.) and mustard (Brassica juncea L. Czern. and Coss). J. Agron. Crop Sci. 185:49–54.
- Canadian Department of Agriculture. 1972. Soil survey of the Tawatinaw map sheet (83-I): Report no. 29—Alberta soil survey. Canadian Dep. of Agric., Soil Res. Inst., Univ. of Alberta, Edmonton, AB, Canada.
- Canadian Grain Commission. 2001. Quality monitoring of Canadian oilseed crops: Oilseed quality tests [Online]. Available at www.grainscanada.gc.ca/Grl/oilseeds/oilseeds-e.htm#oilseedtests (verified 17 May 2004). Canadian Grain Commission, Winnipeg, MB.
- Canola Council of Canada. 2001. The growers manual [Online]. Available at http://www.canola-council.org/production/effect_n.html (verified 17 May 2004). Canola Council of Canada, Winnipeg, MB, Canada.
- Carter, M.R. 1993. Soil sampling and methods of analyses. Can. Soc. of Soil Sci., Pinawa, MB, and Lewis Publ., Boca Raton, FL.
- DeClercq, D.R., and J.K. Daun. 1998. Quality of western Canadian canola: 1998. Canadian Grain Commission, Winnipeg, MB, Canada.
- DeClercq, D.R., and J.K. Daun. 1999. Quality of western Canadian canola: 1999. Canadian Grain Commission, Winnipeg, MB, Canada.
- DeClercq, D.R., and J.K. Daun. 2000. Quality of western Canadian canola: 2000. Canadian Grain Commission, Winnipeg, MB, Canada.
- Etiegni, L., A.G. Campbell, and R.L. Mahler. 1991. Evaluation of wood ash disposal on agricultural land: I. Potential as a soil additive and liming agent. Commun. Soil Sci. Plant Anal. 22:243–256.
- Environment Canada. 2002. Canadian climate normals 1971–2000: Athabasca Alberta. [Online]. Available at www.climate.weatheroffice.ec.gc.ca/climate_normals/stnselect_e.html (modified 24 July 2003; verified 17 May 2004). The Green Lane Environment Canada, Ottawa, ON.
- Grant, C.A., and L.D. Bailey. 1993. Fertility management in canola production. Can. J. Plant Sci. 73:651–670.
- Grant, C.A., W.T. Buckey, L.D. Bailey, and F. Selles. 1998. Cadmium accumulation in crops. Can. J. Plant Sci. 78:1–17.
- Grewal, H.S., R.D. Graham, and J. Stangoulis. 1998. Zinc–boron interaction effects in oilseed rape. J. Plant Nutr. 21:2231–2243.
- Haneklaus, S., H.M. Paulsen, A.K. Gupta, E. Bloem, and E. Schnug. 1999. Influence of sulphur fertilization on yield and quality of oilseed rape and mustard. In New horizons for an old crop. Proc. Int. Rapeseed Congr., 10th, Canberra, ACT, Australia [Online]. Available at www.regional.org.au/au/gcirc/2/13.htm (verified 28 May 2004). The Regional Inst. Ltd. Online Community Publ., Gosford, NSW, Australia.
- Huang, H., A.G. Campbell, R. Folk, and R.L. Mahler. 1993. Wood ash as a liming agent and soil additive for wheat: Field studies. Commun. Soil Sci. Plant Anal. 23(1/2):25–33.
- Iqbal, M.C.M., G. Robbelen, and C. Mollers. 1995. Biosynthesis of glucosinolates by microspore derived embryoids and plantlets in vitro of Brassica napus L. Plant Sci. 112:107–115.
- Krejsl, J.A., and T.M. Scanlon. 1996. Evaluation of beneficial use of wood-fired boiler ash on oat and bean growth. J. Environ. Qual. 25:950–954.[Abstract/Free Full Text]
- Lickacz, G. 2002. Wood ash—an alternative liming material for agricultural soils. Agdex 534–2: Publ. Branch. Agric., Food, and Rural Dev., Edmonton, AB, Canada.
- McClellan, D., L. Kott, W. Beversdorf, and B.E. Ellis. 1993. Glucosinolate metabolism in zygotic and microspore-derived embryos of Brassica napus L. J. Plant Physiol. 141:153–159.
- McCurdy, S.M. 1990. Effects of processing on the functional properties of canola/rapeseed protein. J. Am. Oil Chem. Soc. 67:281–284.
- Meyers, N.L., and M.J. Kopecky. 1998. Industrial wood ash as a soil amendment for crop production. Tappi J. 81:123–130.
- Mulvaney, R.L. 1996. Nitrogen—inorganic forms. p. 1155–1157. In D.L. Sparks et al. (ed.) Methods of soil analysis. Chemical methods. SSSA Book Ser. 5. SSSA and ASA, Madison, WI.
- Muse, J.K., and C.C. Mitchell. 1995. Paper mill boiler ash and lime by-products as soil liming materials. Agron. J. 87:432–438.[Abstract/Free Full Text]
- National Research Council Subcommitte on Mineral Toxicity in Animals. 1980. Mineral tolerance of domestic animals. The National Academies Press, Washington, DC.
- Naylor, L.M., and E. Schmidt. 1986. Agricultural use of wood ash as a fertilizer and liming material. Tappi J. 69:114–119.
- Naylor, L.M., and E. Schmidt. 1989. Paper mill wood ash as a fertilizer and liming material: Field trials. Tappi J. 72:199–203.
- Nuttal, W.F., H. Ukrainetz, J.W.B. Stewart, and D.T. Spurr. 1987. The effect of nitrogen, sulphur, and boron on yield and quality of rapeseed (Brassica napus L. and B. campestris L.). Can. J. Soil Sci. 67:545–559.
- Patterson, S.J., S.N. Acharya, J.E. Thomas, A.B. Bertschi, and R.L. Rothwell. 2004. Effect of land application of wood ash on total biomass and grain yield of barley and canola. Agron. J. 96(4): (in press).
- Rosa, E., R.K. Heaney, R. Fenwick, and C.A.M. Portas. 1997. Glucosinolates in crop plants. Hortic. Rev. 19:99–215.
- Salisbury, F.B., and C.W. Ross. 1992. Plant physiology. 4th ed. Wadsworth Publ. Co., Belmont, CA.
- SAS Institute. 2001. SAS/STAT user's guide. Version 8.2. SAS Inst., Cary, NC.
- Vance, E.D. 1996. Land application of wood-fired and combination boiler ashes: An overview. J. Environ. Qual. 25:937–944.[Abstract/Free Full Text]
TOP
ABSTRACT
INTRODUCTION
