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Soil Science Society of America Journal 66:171-178 (2002)
© 2002 Soil Science Society of America

DIVISION S-4 - SOIL FERTILITY & PLANT NUTRITION

Nutrient Supply and Neutralizing Value of Alfalfa Stem Gasification Ash

Morteza Mozaffaria, Michael P. Russelleb, Carl J. Rosen*,a and Edward A. Natera

a Dep. of Soil, Water, and Climate, 439 Borlaug Hall, 1991 Upper Buford Circle, Univ. of Minnesota. St. Paul, MN 55108
b USDA–ARS U.S. Dairy Forage Research Center (Minnesota Cluster) and Dep. of Soil, Water, and Climate, 439 Borlaug Hall, Univ. of Minnesota. St. Paul, MN 55108

* Corresponding author (crosen{at}soils.umn.edu)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Energy generation from biomass is an environmentally sound alternative to other energy producing technologies. Pilot studies have indicated that alfalfa (Medicago sativa L.) is a suitable feedstock for energy generation via the gasification process. The resulting ash is a potential liming agent and a source of plant nutrients. A growth chamber study was conducted with three soils to evaluate the potential use of this ash as a soil amendment. Corn (Zea mays L.) received 13 treatments: control, K and/or P fertilizer, seven ash rates (0.6 to 14.6 g ash kg-1 soil), and one ash rate with K or P fertilizer. Soil pH increased with ash application on all soils. Ash application increased ammonium acetate-exchangeable K, Ca, and Mg, and Olsen P in soil and decreased DTPA-extractable soil Fe, Mn, Ni, and Pb. Averaged across the three soils, slopes of the cations recovered in plant and soil vs. cations applied in the ash were 0.48, 0.21, and 0.22 of total ash K, Ca, and Mg, respectively (r2 > 0.97). Ash significantly increased plant K and Mo, and decreased Mg, Mn, and Zn concentration. Tissue P concentrations were not affected by ash, but increased with P fertilizer. Phosphorus fertilizer increased plant dry mass (DM), but K fertilizer did not, thus K did not limit yield. Alfalfa stem gasification ash is a potential liming agent, a source of K, and would not lead to excessive accumulation of trace elements in soil or plants when applied at rates based on lime or K need.

Abbreviations: CCE, calcium carbonate equivalent • DM, dry matter • ICP-AES, inductively coupled plasma atomic emission spectroscopy


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
ASH HAS BEEN RECOGNIZED as an excellent soil amendment since well before Jared Eliot wrote in 1748, "Ashes is allowed on all hands to be some of the best dressing or manure for land; it enricheth much and lasts long; but the misery is we can get but little" (Eliot, 1934; Carman, 1934). Eliot was referring mainly to wood and coal ash, which are available today in large amounts from electricity generation. Effects of coal and wood ash on soil chemical properties, and on plant yield and elemental composition have been investigated, and recent reviews include Hammermeister et al. (1998) on coal ash and Mitchell and Black (1997) and Vance (1996) on wood ash.

The major effects of land application of ash are changes in soil pH and nutrient availability. Ash has been used historically and primarily as a liming agent or K source. The liming potential or calcium carbonate equivalent (CCE) of ash is dependent both on the type of ash and soil chemical properties (Clapham and Zibilske, 1992). Wood ash is generally rich in oxides, hydroxides, and carbonates of Ca, K, and Mg, and contains small quantities of micronutrients (Erich and Ohno, 1992; Mitchell and Black, 1997).

Ash application influences availabilities of plant micronutrients either directly through addition of its micronutrients constituents or indirectly through the modification of soil pH. Increased availability of B and Mo has been reported in soils amended with ash from power plants (Codling and Wright, 1998; Hammermeister et al., 1998). Clapham and Zibilske (1992) reported that wood ash application increased acid-extractable (pH 3, 1 M ammonium acetate [NH4OAc]) soil Fe, Zn, Cu, and Mn, but in another study, wood ash decreased extractable Fe and Al (Naylor and Schmidt, 1986).

Modification of soil chemical properties by ash application has resulted in altered elemental composition of plants. Wood ash increased the K concentration in corn and winter wheat (Triticum aestivum L.) in greenhouse studies (Erich, 1991; Etiegni et al., 1991a) and alfalfa in field studies (Meyers and Kopecky, 1998). Wood ash at rates below 20 g kg-1 increased P concentration in wheat (Etiegni et al., 1991a). Other studies have shown that P availability can increase or decrease in ash-amended soils (Erich, 1991; Voundinkana et al., 1998; Moliner and Street, 1982; Elseewi et al., 1980). Application of either coal fly ash or wood ash decreased tissue Zn, Fe, and Mn, and increased B and Mo (Elseewi et al., 1980; Francis et al., 1985; Naylor and Schmidt, 1989). Application of wood-fired boiler ash decreased the concentrations of Mn and Cu in bean (Phaseolus vulgaris L.) plants (Krejsl and Scanlon, 1996). These effects on plant micronutrient concentration may have implications for human or animal health.

Plant DM production has increased, decreased, or remained unchanged after coal or wood ash application, depending on factors such as type and rate of ash application, plant species, and soil properties. Oat (Avena sativa L.) grown in soil amended with 30 Mg ha-1 of wood-fired boiler ash produced significantly higher DM than plants grown in nonamended soil, but DM declined at 50 Mg ha-1 ash (Krejsl and Scanlon, 1996). Wood ash application had no effect on production of spinach (Spinacia oleracea L.) in a greenhouse study (Clapham and Zibliskie, 1992) nor on wheat yield in a field study (Huang et al., 1992).

In recent years, utilization of herbaceous species as biomass fuel for electricity generation has been viewed as an environmentally viable option. Preliminary studies have indicated that alfalfa stems are suitable feedstock for energy generation via the gasification process (Wilbur et al., 1998). If the ash from alfalfa gasification can be utilized as a soil amendment, then economic viability and public acceptance of this alternative energy source may increase. Chemical characterization has indicated that alfalfa ash is a potential liming agent, its macronutrient content is equivalent to a 1-1-10 fertilizer, and it also contains other soluble elements (Mozaffari et al., 2000a). A greenhouse experiment with corn indicated that alfalfa ash might be a source of K and a good liming material for acid soils (Mozaffari et al., 2000b). The objective of this research was to further evaluate these potential benefits and the potential deleterious effects of alfalfa stem gasification ash on soil chemical properties and on early corn growth and shoot composition.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Soils and Ash
The experiment was conducted with three representative agricultural soils of Minnesota: a Hubbard sand (sandy, mixed, frigid Entic Hapludolls), a Waukegan silt loam (fine silty over sandy or sandyskeletal, mixed, mesic Typic Hapludolls), and a Wykeham sandy loam (fine-loamy, mixed, superactive, frigid Aquic Hapludalfs). A bulk sample of 20 cm of each soil was collected from the surface and was air dried. Selected chemical and physical characteristics of the three soils are listed in Table 1. All sites were chosen based on our expectation that a crop K response would be likely. The Hubbard is an acid, very high P, and medium K soil; Waukegan is a slightly acid, high P, and medium K soil; and Wykeham is a neutral pH, low P, medium K soil.


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  		Table 1. Selected physical and chemical properties of the Hubbard, Waukegan, and Wykeham soils used in the growth chamber experiment.

 
The alfalfa stem ash used in this study was the byproduct of a gasification test that utilized alfalfa grown in Minnesota as feedstock. The fly ash had a pH of 11.8 (1:1 w/w H2O), CCE of 400 g kg-1 (Johnson, 1990a), 9 g P kg-1, and 100 g K kg-1 in the ammonium citrate extract (Johnson, 1990b), and 13 g kg-1 total N. The saturated paste extract had an electrical conductivity (EC) of 130 dS m-1 and contained 78 g K L-1, 147 mg P L-1, 4.5 mg B L-1, and 20 g Cl L-1. Comprehensive chemical characterization of the ash was reported by Mozaffari et al. (2000a).

Experimental Treatments
The 13 treatments included a control, seven fly ash rates ranging from 0.61 to 14.6 g ash kg-1 soil (equivalent to 0.9 to 21.6 Mg ha-1), K fertilizer, P fertilizer, K + P fertilizer, ash + K fertilizer, and ash + P fertilizer. Reagent grade KCl and secondary dibasic CaHPO4 were used as sources of K and P fertilizer, respectively. Detailed information on fertilizer and ash rates and the amount of K and P supplied by each treatment is provided in Table 2. The fertilizer treatments were included to assess whether corn responded to K or P in these soils. Soil and amendments for all four replications of each treatment were mixed thoroughly in one batch to reduce variability among replications. Ammonium nitrate was added to all treatments at the rate of 0.18 g kg-1 at planting and top-dressed at the same rate 10 and 20 d after seedling emergence (total of 0.54 g N kg-1 NH4NO3). After mixing, three replications of each treatment were prepared by placing 1.4 kg of amended soil in a 15-cm diam. 2.1-L plastic pot placed on a 20-cm diam. saucer. Six corn seeds (Pioneer Hi-Bred 37301) were planted in each pot. Treatments were randomly arranged by soil within three growth chambers, with each replication assigned to a separate growth chamber. A 14-h photoperiod at about 400 µmol m-2 s-1 of photosynthetic photon flux was provided by fluorescent lights and temperature was maintained at 30°C during the light and 15°C during the dark. Seedlings were thinned to one per pot 1 wk after emergence. Daily watering maintained soil moisture at approximately field capacity. Leaching loss of soluble elements was minimized by returning any water leached into the saucers to the soil. Corn shoots were harvested 39 d after plant emergence. Plants were dried in a forced air oven at 65°C and their dry weights were measured. Dried plants were ground and a subsample was used for chemical analysis. After plant harvest, composite soil samples of five 2.5-cm diam. cores were collected from each pot.


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  		Table 2. Fertilizer and ash treatments used in the growth chamber study and the amount of K and/or P supplied by each treatment.

 
Chemical Analysis of Soil and Plant Samples
Soil samples were extracted for exchangeable K, Na, Ca, and, Mg by 1 M NH4OAc (Sumner and Miller, 1996) and for Cu, Zn, Fe, Mn, Cr, Cd, Ni, and Pb by 0.005 M DTPA (adjusted to pH 7.3) extraction (Reed and Martens, 1996). Concentrations of the elements in all extracts were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) (Dahlquist and Knoll, 1978). Soil P was extracted by Olsen method (Kuo, 1996) and determined by ICP-AES. Soil pH and EC in 1:1 soil/water (w/w) suspension was measured as described by Watson and Brown (1998) and Whitney (1998), respectively.

Plant samples were digested in HNO3 in a microwave by the wet ashing procedure (Miller, 1998) and concentrations of P, K, Ca, Mg, Na, Al, Fe, Mn, Zn, Cu, B, Pb, Ni, Cr, Cd, and Mo were measured by ICP-AES.

Statistical Treatment of Data
The SAS software package was used for statistical analysis of the data (SAS, 1996). Analysis of variance (ANOVA) was used to discern significant treatment effects on soil chemical properties, and on corn yield or elemental concentration. Experimental design was a split plot (soil as the main plot) randomized complete block. Only significant effects (P < 0.05) are presented. When the ANOVA indicated a significant soil by treatment effect for soil or plant responses, the response variables for each soil were analyzed and are presented separately. Regression was used to generalize soil or plant response to ash application (Barrow and Mendoza, 1990; SAS, 1996), when warranted by linear, quadratic, or residual terms of orthogonal contrasts for ash rate. The inorganic fertilizer treatments and fertilizer plus ash treatments were not included in regression equations.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSION
 REFERENCES
 
Soil Chemical Properties
Soil pH and Electrical Conductivity
Unlike our earlier results, which showed no pH response to ash in a high pH clay loam soil and a linear response in the Hubbard sand (Mozaffari et al., 2000b), all three soils in this experiment showed curvilinear pH responses to ash addition pH (Fig. 1 , Table 3). The earlier experiment included ash rates only to 6.4 g kg-1 soil, and data from Hubbard soil in the current experiment confirmed this linear relationship of pH to ash application up to 7.3 g kg-1 (r2 = 0.98). In the two acid soils, 2.2 or 2.8 g kg-1 alfalfa stem ash was required to increase pH to 6.5 (Fig. 1), a level adequate for most major crops. Other greenhouse studies have also demonstrated an increase in soil pH with wood ash or combined boiler ash (Meyers and Kopecky, 1998; Krejsl and Scanlon, 1996; Etiegni et al., 1991a).



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  		Fig. 1. Response of chemical characteristics of Hubbard, Waukegan, and Wykeham soils to alfalfa stem gasification fly ash.

 

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  		Table 3. Probabilities of a greater F statistic in single degree-of-freedom orthogonal contrasts in the ANOVA for the effect of ash on soil pH, EC, Olsen P, ammonium acetate-exchangeable cations, and DTPA-extractable metals, and on plant response.

 
Soil EC increased with ash application in all three soils (Fig. 1, Table 3). Ranking of soil EC did not change with ash rate, and the highest observed value was 1.82 dS m-1 in Wykeham soil. In Hubbard and Waukegan soils, addition of 1 g kg-1 of ash increased the EC by about 0.03 dS m-1 (y = 0.14 + 0.025x for Hubbard, r2 = 0.94). Rate of increase was twice as fast in Wykeham soil, at 0.056 dS m-1 for each g kg-1 ash addition (Fig. 1). The increase in salinity because of this ash is similar to responses to wood and coal fly ash (Clapham and Zibilske, 1992; Sale et al., 1996; Matsi and Keramidas, 1999).

Exchangeable Cations
Ash application increased exchangeable K, Ca, and Mg in all soils, and increased Na in Waukegan and Wykeham soils (Table 3). A linear relationship existed between ash application rates and the levels of exchangeable Ca, Mg, and Na (r2 > 0.80, except no effect on Na in Hubbard soil), whereas K increased more quickly, the higher the ash rate (Fig. 1) (data not shown for Ca, Mg, and Na). In all three soils, the ranking of increases in exchangeable cations followed the pattern K > Ca > Mg, consistent with concentrations of these elements in the ash (Mozaffari et al., 2000a).

The amount of K, Ca, and Mg recovered in plant and soil (the sum of each exchangeable cation in postharvest soils plus the amount of each cation removed by the plants) was correlated with the total amount of each cation added by the ash. Averaged across the three soils, slopes of the cations recovered in plant and soil vs. total amount of each cation applied in the ash were 0.48, 0.21, and 0.22 (r2 > 0.97) for K, Ca, and Mg, respectively. About 60% of the ammonium citrate extractable K supplied by ash was accounted for in soil and shoot tissue, averaged across soils. Based on plant K uptake alone, and using the first four ash rates (linear fit r2 > 0.99), apparent ash K absorption by the 39-d-old corn was 62% in Hubbard soil and 40% in Waukegan soil. Poor plant growth on the Wykeham soil resulted in a recovery of only 7% of applied K (linear fit r2 = 0.67). The increase in exchangeable cations because of ash application is consistent with results of other laboratory, greenhouse, and field studies conducted with other types of biomass-derived ashes (Muse and Mitchell, 1995; Naylor and Schmidt, 1989; Ohno and Erich, 1990). Our results indicate that, similar to other ashes, alfalfa stem gasification ash is a source of basic cations, particularly K.

Available Phosphorus
Ash application increased Olsen-extractable P in all three soils (Fig. 1, Table 3). Olsen P in Waukegan and Wykeham soil increased to 29 and 21 mg kg-1, respectively. This increase was because of P addition in the ash, perhaps to the liming effect of ash on P availability in Waukegan soil, and possibly to less neutralization of the Olsen bicarbonate extractant in acid soils as soil pH rose. Corn grain yield grown on soils with Olsen P values greater than 16 mg kg-1 is not expected to respond to additional P (Rehm et al., 1995), but early corn growth in the field is often greater with higher soil test P.

The relationship between ash application rate and extractable P was best described by linear regression, except in Hubbard soil, which showed no response until more than 7.5 g ash kg-1 soil was applied (Fig. 1). In Wykeham and Waukegan soils, addition of 1 g kg-1 of ash (9 mg citrate-soluble P kg-1 soil) increased extractable P by about 1 mg kg-1. The rate of increase in Olsen P on Hubbard soil was twice as fast, 2.2 mg kg-1 (based on the highest four ash rates to avoid the plateau). Biomass ash often increases soil extractable P. For example, wood ash at the rate of 20 g kg-1 increased the Bray-2 extractable P to 13.5 mg kg-1 from 7.9 in the nonamended control (Voundinkana et al., 1998). These ratios of applied P to soil test increase are well within the range of results obtained with fertilizer P in the field (Randall et al., 1997), which implies that alfalfa ash may provide P to crops.

Available Metals and Nutrients
DTPA-extractable Zn, Cd, Cr, and Cu were below 2.5, 0.08, 0.07, and 1.1 mg kg-1, respectively, and in our experiment were not affected by ash application.

DTPA-extractable Fe, Mn, Ni, and Pb were reduced by ash application (data not shown), with the exception that Mn increased from 12 to 23 mg kg-1 in Hubbard soil when ash rate increased from 9.8 to 14.6 g kg-1 ash. Extractable metal concentrations were low in these soils initially and reduced extractability was probably because of the liming effect of the ash. This liming effect on DTPA-extractable metals has been reported for other alkaline biomass ashes (Voundinkana et al., 1998; Krejsl and Scanlon, 1996).

The data suggest that metal toxicity is unlikely in soils amended with alfalfa biomass ash rates based on realistic crop yield goals and soil test value. However, reduced availability of micronutrients associated with very high rates of alfalfa ash may limit potential crop growth. The data also suggest that alfalfa ash may have potential for remediation of acid or neutral soils contaminated with high levels of metals.

Elemental Composition of Young Corn
There was a significant soil by treatment interaction for K, P, Mn, and Mo, but not for Zn and Mg. Where this interaction occurred, responses to ash are discussed for each soil; otherwise, responses were averaged over soils.

Potassium Concentration and Uptake
Concentration of K in plants grown in the nonamended Hubbard, Waukegan, and Wykeham soils was 9, 10, and 29 g kg-1, respectively, and both K fertilizer and ash increased K concentration (Fig. 2) (data shown for ash treatments only). The effect of ash on plant K was evident at the lowest rate of ash (0.61 g kg-1) and approached a plateau at an ash rate between 2 and 6 g kg-1, depending on the soil. Initial response on Hubbard and Waukegan soils was comparable, despite lower DM accumulation by plants grown in Waukegan (discussed below), perhaps reflecting the similar original soil K levels.



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  		Fig. 2. Effect of alfalfa stem gasification fly ash (closed symbols) and fertilizer K (open symbols) on K concentration in corn plants grown in Hubbard, Waukegan, and Wykeham soils for 39 d under growth chamber conditions.

 
Ash application increased K uptake by corn in all soils, reaffirming that ash supplied K to the crop (Fig. 3) . At the highest ash application rate, K uptake was at least 2.6 times greater than in the nonamended soil. Moreover, plant K uptake was 13% higher with ash than fertilizer (P < 0.01) at comparable rates of added K (120 mg K kg-1 soil, 1.2 g ash kg-1 soil).



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  		Fig. 3. Effect of alfalfa stem gasification fly ash (closed symbols) and fertilizer P or K (open symbols) on corn shoot dry mass and K and P accumulation after 39 d under growth chamber conditions.

 
Phosphorus Concentration and Uptake
When all ash and fertilizer treatments were included, ANOVA indicated a significant treatment effect on plant P. Concentration of P in plants grown in the fertilizer-amended soil was higher than in the control (P < 0.01). Phosphorus concentration of plants grown in the P-fertilizer treatment in Hubbard, Waukegan, and Wykeham soils was 2.9, 2.0, and 1.8 g kg-1, respectively, compared with 2.3, 1.7, and 1.2 g kg-1 in the respective nonamended soils. In all soils, citrate-soluble P from fertilizer was more available than citrate-soluble P from ash, regardless of ash rate. Corn P concentration did not respond to ash application. We cannot explain the lack of plant P concentration response in Wykeham soil, where both plant and soil P levels appeared to be deficient, but the ash effect observed here is consistent with the work of Clapham and Zibilske (1992), who reported that P concentration in spinach was not affected by wood ash application. However, other researchers have reported that P from wood ash was available for plant uptake (Etiegni et al., 1991a; Erich, 1991). In our work, there was a very small but significant (P < 0.1) increase in P uptake in Wykeham soil only (Fig. 3), despite constant tissue P concentrations.

Other Elements in Corn
Ash application reduced plant Mg, Mn, and Zn concentrations (P < 0.01). Corn shoot Mg concentration declined by 170 mg kg-1 for each 1000 mg kg-1 increase in shoot K concentration on the two finer-textured soils, and by 60 mg kg-1 in the Hubbard sand. This type of Mg response is very common where K-supplying amendments are used (Munson, 1968; Dibb and Thompson, 1985). As with high K fertilizer application rates, we suspect that high alfalfa biomass ash application rates may induce Mg deficiency under some conditions. Such reductions can potentially limit crop yield and forage quality. Low Mg in forage crops can cause grass tetany in livestock (Preston and Linser, 1985).

The decline in plant Zn concentration with increasing ash rate was likely because of increased soil pH. Although we did not detect a change in DTPA-extractable Zn in soil in the ANOVA, plant Zn declined by 50% with a 1 unit rise in pH. Ash application decreased plant Mn only in Hubbard soil and only with the first increment of ash (from 150–95 mg Mn kg-1), consistent with, although greater than, the decline in extractable soil Mn from 34 to 28 mg kg-1.

In contrast to Mg, Mn, and Zn, ash increased Mo concentration in corn by four-fold at the highest rate of ash application (Table 4). At the highest ash rate, Mo concentration in plants grown in Hubbard, Waukegan, and Wykeham soils was 5.9, 2.6, and 5.5 mg kg-1, respectively. Increased availability of Mo could be because of the direct effect of Mo added by the ash, which contained 10 mg kg-1 of soluble (saturated extract) Mo and 26 mg kg-1 total Mo (Mozaffari et al., 2000a). Thus, alfalfa stem biomass ash is within the range of 5.3 to 39.3 mg kg-1 Mo reported in 15 coal fly ashes (Doran and Martens, 1972). Molybdenum response may also have been because of the liming effect of the ash, because solubility and availability of Mo increases with increasing pH (Adriano, 1980). Under field conditions, plant Mo toxicity has been very rare (Moraghan and Mascagni, 1991). The critical toxicity level for Mo in plants is reported to be 200 to 1000 mg kg-1 tissue DM (Romheld and Marschner, 1991).


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  		Table 4. Probabilities of a greater F statistic in single degree-of-freedom orthogonal contrasts in the analysis of variance for the effect of ash on elemental concentration of corn plants.

 
Much lower Mo concentrations in forage, however, may induce molybdenosis in livestock, which is a Cu deficiency-related problem. Some researchers have suggested that Mo concentrations >5 to 10 mg kg-1 in plants are hazardous for livestock (James et al., 1968). Others have proposed a Cu/Mo ratio of 4:1 or greater to insure the Cu requirement of animals is met (McDowell, 1992), and some researchers have suggested that a Cu/Mo ratio lower than 2:1 is likely to cause molybdenosis (Dollahite et al., 1972). At the ash application rate of 2.44 g kg-1, the Cu/Mo ratio of young corn plants grown in Hubbard, Waukegan, and Wykeham soils was 6.2, 7.2, and 3.9, respectively, and declined to 4.9, 3.5, and 2.4, respectively, with 4.88 g kg-1 ash. We do not know what Cu/Mo ratios would occur in corn silage grown under field conditions, but these results raise the possibility that feeding animal with forage crops grown on soils amended with very high ash rates may present a potential nutritional problem if supplemental Cu is not included in the animal diet.

Concentrations of B, Al, and Cu in young corn plants were not affected by ash application (data not shown). Therefore, unlike coal ash where B toxicity has been a major concern (Sims et al., 1995), B toxicity does not appear to be a potential problem for plants grown in soils amended with these rates of alfalfa ash.

Corn Dry Mass
Corn shoot DM data are presented for each soil separately because the treatment by soil interaction was significant. When all treatments (ash and fertilizer) were included in the analysis of variance, a highly significant treatment effect was observed regardless of soil type. Shoot production was not affected by K fertilizer alone, but increased with P fertilizer in all soils (Table 5). In all soils, shoot mass in the ash + K treatment did not differ from the ash-only treatment at the same rate. The only case where ash application rate appeared to increase shoot DM was in Wykeham soil (Fig. 3), but most of that response appeared to be because of some ash-mediated effect other than to K supplied by ash. These data suggest that in this container study, shoot DM was not enhanced by K addition, regardless of the K source.


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  		Table 5. Effect of alfalfa ash and fertilizer on corn dry mass production after 56 d in Hubbard, Waukegan, and Wykeham soil.

 
Corn DM response to ash was dependent on soil type (Fig. 3, Table 3). Low rates of ash increased and high rates of ash decreased DM in Hubbard soil. In contrast, DM increased linearly with ash in Wykeham soil, but was not affected in Waukegan soil. Lower yield of plants grown in Hubbard soil at the two highest rates of ash may be because of reduced Ca and Mg uptake associated with high K supply. At harvest, the corn plants grown in Hubbard soil were ~30 cm tall. The critical Mg or Ca concentration for field-grown corn at that height in Minnesota is 3 g kg-1 (Overdahl, 1987), whereas at the highest rate of ash application, concentrations of Ca and Mg in corn plants grown in Hubbard soil were 2.4 and 2.1 g kg-1, respectively. Etiegni et al. (1991b) reported that bean yield started to decline when K supply by wood ash was more than 460 kg ha-1. In contrast to the Hubbard soil, Ca concentration of plants grown in Waukegan and Wykeham soils at the highest ash rate was 4.0 and 9.6 g kg-1, respectively, and concentrations of Mg were 2.7 and 4.3 g kg-1, respectively.

In Hubbard soil, salinity could be another factor contributing to yield reduction at high ash rates. The amount of moisture retained by the sand-textured soil at field capacity was very low (Table 1); therefore, the actual concentration of soluble salts in this soil was considerably higher than in either Waukegan or Wykeham soil, a condition not reflected in 1:1 soil/water extraction. It is also possible that an interaction between high P availability and low Zn contributed to decreased DM at high ash rates in the Hubbard soil. Further research is needed to determine the cause of this yield decline at high ash rates.


   CONCLUSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
REFERENCES
 
This growth chamber study indicated that alfalfa stem gasification ash is a potentially useful source of K and possibly P, and is an effective liming agent in acid soils. At ash application rates exceeding 7.5 g kg-1, plant growth declined to less than one-half the maximum on the sand-textured soil, but no yield depression occurred on finer-textured soils. At very high rates of ash excessive availability and uptake of Mo may become a forage quality concern. We conclude that this ash is not likely to pose significant risk of excessive inorganic element and metal accumulation in either soil or plants, when used at rates based on crop yield goal and soil test value. The nutrients in the alfalfa stem gasification ash can potentially be safely recycled in the agroecosystem, providing added value to this method of renewable electrical energy production.


   ACKNOWLEDGMENTS
 
This work was supported in part with funds approved by the Minnesota Legislature, ML 1997, Chapter 216, Sec. 15, Subd. 12 (c) as recommended by Legislative Commission on Minnesota Resources from the Minnesota Future Resources Fund and by funds from Minnesota Valley Alfalfa Producers, through a grant provided by United States Department of Energy.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Joint contribution of the Minnesota Agric. Exp. Stn. and the USDA-ARS.

1 Mention of a trademark or a proprietary product does not constitute a guarantee or warranty of the product by the Univ. of Minnesota or USDA and does not imply its approval to the exclusion of other products that may also be suitable. Back

Received for publication August 8, 2000.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 




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The SCI Journals Agronomy Journal Crop Science
Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome