Impact of Sugarcane Bagasse Ash as an Amendment on the Physical Properties , Nutrient Content and Seedling Growth of a Certified Organic Greenhouse Growing Media

Sugarcane bagasse is the fibrous material remaining after removing the sucrose, water, and other impurities (filter mud) from the millable sugarcane. Louisiana sugarcane mills use a portion of the sugarcane bagasse to produce steam power to run equipment within the mill and/or as a boiler fuel for the clarification, evaporation, and crystallization processes. Sugarcane bagasse ash (SBA) is a by-product of the thermal conversion of the sugarcane bagasse. The purpose of this research was to investigate the use of SBA as an amendment to soilless planting media for the production of vegetable seedlings. The SBA was combined by volume with a commercial certified organic soilless growing media into 5 combinations (0%:100%, 25%:75%, 50%:50%, 75%:25%, and 100%:0%, SBA and growing media, respectively). Bean (Phaseolus vulgaris L.) var. ‘Bowie’ and Chinese kale (Brassica alboglabra) var. ‘South Sea’ were planted in each of the 5 different planting mixtures. As the percentage of SBA increased from 0% to 100%, the bulk densities increased, 0.118 to 0.712 g/cm, while the porosity, water saturation percentage, and water at field capacity decreased. Increasing the SBA percentage significantly impacted total exchange capacity, pH, organic matter, estimated nitrogen release, and all other nutrients measured, except for sodium. The research indicates that the addition of SBA can enhance bean and Chinese kale seedling growth depending on the percentage of the ash added to the growth media. Bean and Chinese kale harvest parameters typically peaked at 25% SBA, and then decreased with increasing SBA %. Adding 25% SBA did benefit the seedling growth by providing additional nutrients for seedling growth, while reducing the cost of production by supplementing the more expensive greenhouse media by a readily available by-product of the sugarcane industry. Increasing the SBA % to 50% or greater is not recommend. Additional research is needed to determine the percentage above 25% and below 50% SBA that would still benefit seedling plant growth.


Sugarcane Bagasse Ash Production
It is very common for Louisiana sugarcane mills to burn a portion of the sugarcane bagasse to produce steam power to run equipment within the mill and/or as a boiler fuel for the clarification, evaporation, and crystallization processes.Sugarcane bagasse ash (SBA) is a by-product of the thermal conversion of the sugarcane bagasse.Depending on the source of the sugarcane, harvesting methods and thermal conversion efficiency at the mill, the percentage of ash produced from bagasse typically represents a small percentage, 1.5 to 3.0% by weight, of the original sugarcane bagasse (Amin, 2011;Garcıà-Pèrez, 2002).And, although SBA content is low (1.5-3.0%)compared to other agricultural sources such as rice straw, 14.5% (Guo et al., 2009) and wheat straw, 8.6% (Biricik et al., 1999), the large volume of bagasse used for fuel results in massive amounts of SBA that necessitates economically and environmentally handling.If the estimated 80% (Pandey et al., 2000) of the 3.5 million mg of bagasse produced each year in Louisiana is used for energy conversion at the sugarcane mills, the SBA produced in Louisiana each year would range from 42,000 to 84,000 mt, and an estimated 2.25 to 4.5 million mt of sugarcane bagasse ash globally.

Physical Analysis
Each of the 5 soilless media mixtures were analyzed for bulk density (g/cm 3 ), porosity (%), water saturation percentage, and water at field capacity (5).Each physical test on the 5 soil media mixtures were repeated 4 times.The measuring chamber was a cylinder with a 40 mm inner diameter and an interior height of 64.5 mm with a measured volume of 81 cm 3 .

Chemical Analysis
Four representative samples for each media combination were collected and chemically analyzed (Brookside Laboratories,Inc.,200 White Mountain Drive,New Bremen,Ohio,45869,www.blinc.com).The chemical data were subjected to ANOVA procedure and mean separation using LSD with P = 0.05 (SAS Inc., SAS, Ver.9.0, Cary, NC).

Plant Growth and Analysis
Five seedlings from the center of each tray were harvested 20 days after planting for the bean seedlings and 33 days after planting for the kale.Each seedling was divided into above and below ground plant portions.The above ground portion was measured for plant length by measuring the distance from the media surface to the apical meristem.The upper portion of the plant was further divided into leaves and stalks.The planting media was removed from lower portion of the plants (roots) for measuring.The fresh weight of the leaves, stalks, and the roots were then determined.The plant portions were then oven dried for 2 days at 60 o C and then reweighed to determine dry weights.Plant establishment was determined at harvest by calculating the percentage of Speedling ® planting cells containing viable seedlings.All data were subjected to ANOVA and mean separation using LSD with P = 0.05 (SAS Inc., SAS, Ver.9.0, Cary, NC).

Statistical Analysis
When the statistical analysis determined that there were significant interactions between experiments within plant species and plant growth media (0%, 25%, 50%, 75% and 100% SBA), the results will be discussed by experiments rather than averaged across experiments.Otherwise, when there is not an experiment by growing media interaction, the results will be discussed across experiments.

Physical Analysis: Bulk Density and Porosity
The bulk densities of the media mixtures consistently increased from 0.118 to 0.712 g/cm 3 as the SBA percentage increased from 0% to 100% (Table 1).And, as the media mixtures increased in SBA percentage and bulk density, the porosity, water saturation percentage, and water at field capacity decreased (Table 1).As the growing media's porosity, water saturation and field capacity decreased with higher SBA percentages, the growing media's ability to provide available water to the growing seedlings also decreased (Table 1).Decreased water availability might necessitate increasing irrigation frequency compared to the standard greenhouse media (0% SBA).The increase bulk density and decrease in the other media parameters may by increase the potential plant stress in a greenhouse environment.
Table 1.Impact of sugarcane bagasse ash (SBA) percentage of growth medium on growing media bulk density (g/cm 3 ), percent total pore space, percent water saturation, and percent water at field capacity Note.z Percentage of sugarcane bagasse ash (SBA) in the growth medium based on volume; y Means in a column followed by the same lower case letter are not significantly different at P ≤ 0.05, ANOVA.
Although the base saturation percentages of calcium (Ca), magnesium (Mg), potassium (K), other bases, and hydrogen (H) were significantly different among most SBA growing media, the range between the highest and lowest values were not that extreme, except for the percentage of K, which would be expected, and the absence of % H in the 50% to 100% SBA range (Table 4).Although the impact of these differences may not be readily seen in a short term seedling production (3-4 weeks), the impact may be more obvious when seedlings are grown for longer periods of time (4-8 weeks).
Table 4. Impact of sugarcane ash percentage (SBA %) as an amendment on the base saturation percentages for the five sugarcane greenhouse growing mixtures.Note.z Percentage of sugarcane bagasse ash (SBA) in the growth medium based on volume; y Means in a column followed by the same lower case letter are not significantly different at P ≤ 0.05, ANOVA.
All of the essential minor elements concentrations (ppm) of boron (B), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn) and aluminum (AL) increased as the % SBA increased (Table 5).The addition of these extractable essential minor elements through the addition of the SBA has the potential to increase the nutrient status of the growing media.These results may explain earlier research by Webber et al. (2016) where 25% and 75% SBA increased cantaloupe and squash seedling growth, respectively.
Table 5. Impact of sugarcane ash percentage (SBA %) on extractable essential minor elements (ppm) for the five sugarcane bagasse ash (SBA) growing media Note.z Percentage of sugarcane bagasse ash (SBA) in the growth medium based on volume; y Means in a column followed by the same lower case letter are not significantly different at P ≤ 0.05, ANOVA.

Bean
(1) Bean Stalk Lengths and Impact of Population Significant interactions were detected between the planting media and experiments for bean stalk length and plant establishment; therefore, this data will be discussed by experiment (Table 6).In experiments 1 and 2 there were no consistent correlation between SBA content and bean seedling stalk lengths (Table 6).Bean plant establishment was the greatest for the 0% and 25% SBA, along with the 100% SBA in experiment 1 and 25% and 50% SBA for experiment 2 (Table 6).
Table 6.Impact of sugarcane bagasse ash (SBA) percentage of growth medium on bean seedling stalk length (mm) and plant population (%) for two experiments, four replications per experiment, and five harvested seedlings per replication Note.z Percentage of sugarcane bagasse ash (SBA) in the growth medium based on volume; y Means in a column followed by the same lower case letter are not significantly different at P ≤ 0.05, ANOVA.
(2) Bean Seedling Fresh Plant Weights No significant interactions were detected between the experiments and the growth media for the seedling fresh weights of the stalks, leaves, plant tops, and total plant weights, although there was an interaction between experiments and fresh root weights (Table 7).Therefore, except for the fresh root weights, the data will be discussed across both experiments.The 25% SBA produced the greatest bean fresh weights for the stalks, leaves, tops, and whole plants, while the fresh root weights peeked at 0% SBA in experiment 1 (4.67 g) and at 25% SBA in experiment 2 (4.59 g).These results were similar to those reported by Webber et al. (2016) for 25% SBA planting media for cantaloupe seedling production.Note.z Percentage of sugarcane bagasse ash (SBA) in the growth medium based on volume; y Means in a column followed by the same lower case letter are not significantly different at P ≤ 0.05, ANOVA.
(3) Bean Seedling Dry Plant Weights As a result of significant interactions between the planting media and experiments for the dry weights of the bean leaves, plant tops, and total plants, these results will be discussed by experiments (Table 8).Due to the lack of experiment by media interaction, the bean dry stalk and root weights will be discussed across experiments (Table 8).There were small but significant differences for bean dry weights of the leaves, tops, and total seedling weights, but the results were not consistent between experiments or plant materials measured (Table 8).In many cases (i.e.leaves dry weights experiments 1 and 2, top dry weights experiment 1, total plant dry weights experiments 1 and 2), the 25% SBA produced the greatest plant weigh, although not significantly different from all other SBA media combinations (Table 8).The dry weights of the stalks and roots combined across experiments followed a similar pattern as the other dry weights (leaves, tops, and total dry weights) which had the experiment by SBA % interactions (Table 8).Note.z Percentage of sugarcane bagasse ash (SBA) in the growth medium based on volume; y Means in a column followed by the same lower case letter are not significantly different at P ≤ 0.05, ANOVA.
(4) Bean Seedling Summary There were no consistent correlation between SBA content and bean seedling stalk lengths.Bean plant establishment was the greatest for the 0% and 25% SBA, along with the 100% SBA in experiment 1 and 25% and 50% SBA for experiment 2. The 25% SBA produced the greatest bean fresh weights for the stalks, leaves, tops, and whole plants, while the fresh root weights peeked at 0% SBA in experiment 1 and at 25% SBA in experiment 2. There were small but significant differences for bean dry weights of the leaves, tops, and total seedling weights, but the results were not consistent between experiments or plant materials measured.In many cases (i.e.leaves dry weights experiments 1 and 2, top dry weights experiment 1, total plant dry weights experiments 1 and 2), the 25% SBA produced the greatest plant weights, although not significantly different from all other SBA media combinations.The dry weights of the stalks and roots combined across experiments followed a similar pattern as the other dry weights (leaves, tops, and total dry weights) which had the experiment by % SBA interactions.These results were similar to those reported by Webber et al. (2016) for 25% SBA planting media for cantaloupe seedling production.

Chinese Kale Seedling Analysis
Except for the Chinese kale root fresh weights and plant establishment data, there were no significant interactions detected between the experiments and SBA planting media data.As a result, the Chinese root fresh weights and percent plant established will be discuss by experiment (Table 9), while the other harvest data will be discussed across experiments (Tables 10 and 11).
(1) Chinese Kale Seedling Fresh Root Weights and Establishment Although there were significant interactions between SBA growing media and experiments for the Chinese kale fresh root weights and plant establishment, in all cases the values peaked at either 25% or 0% SBA media (Table 9).Note.z Percentage of sugarcane bagasse ash (SBA) in the growth medium based on volume; y Means in a column followed by the same lower case letter are not significantly different at P ≤ 0.05, ANOVA.
(2) Chinese Kale Stalk Lengths, and Fresh Weights of Stalks, Leaves, Tops, and Total Plant The 25% SBA growing media consistently produced the greatest Chinese kale stalk lengths and fresh plant weights (stalks, leaves, tops, and total plant) (Table 10).As the SBA content increased from 25% to 100% SBA, the plant lengths and fresh weights consistently decreased (Table 10).These results follow a similar pattern as the impact of the SBA % on bean fresh weights (Table 7), and cantaloupe seedling data reported by Webber et al. (2016).
Table 10.Impact of sugarcane bagasse ash (SBA) percentage of growth medium on Chinese kale seedling stalk lengths (mm) and plant fresh weights (g) averaged across two experiments, four replications per experiment, and five seedlings per replication.Note.z Percentage of sugarcane bagasse ash (SBA) in the growth medium based on volume; y Means in a column followed by the same lower case letter are not significantly different at P ≤ 0.05, ANOVA.
(3) Chinese Kale Seedling Dry Weights Chinese kale seedling dry weights (Table 11) responded to SBA% in the same manner as the Chinese kale fresh weighs (Table 10).The stalks, leaves, tops, and total plant dry weights peaked at the 25% SBA, and significantly decreased as the percentage of SBA was added to the growing media (Table 11), while root weights were not as significantly different, but tended to decrease as the SBA percentage increased (Table 11).These results are also consistent to those reported by Webber et al. (2016) concerning cantaloupe seedling dry weights.(4) Chinese Kale Seedling Summary Although there are significant interactions between SBA growing media and experiments for the Chinese kale fresh root weights and plant establishment, in all cases the values peaked at either 25% or 0% SBA media.The 25% SBA growing media consistently produced the greatest Chinese kale stalk lengths, and fresh and dry plant weights (stalks, leaves, tops, and total plant).In addition, as the SBA content increased from 25% to 100% SBA, the plant lengths and weights consistently decreased.These results follow a similar pattern as the impact of the SBA % on bean fresh weights (Table 7).Webber et al. (2016) also observed a beneficial impact of adding 25% SBA to a soilless growing media on cantaloupe seedling growth with a corresponding decrease in growth at the higher SBA percentages.

Conclusions
The SBA mixture bulk densities consistently increased from 0.118 to 0.712 g/cm 3 as the SBA percentage increased from 0% to 100%, while the porosity, water saturation percentage, and water at field capacity decreased.As the bulk densities increased and the water holding capacity decreased, the growing media became less conducive to plant growth and more difficult to manage, increasing the potential for plant stress in a greenhouse environment.
Increasing the SBA percentage significantly influenced total exchange capacity, pH, organic matter, estimated nitrogen release, and all other nutrients measured, except for sodium.Although the bean and Chinese kale seedlings neither exhibited deficiency nor toxicity symptoms, the impact of the pH alone would need to be addressed in the future use of SBA depending on the seedlings grown.Additional nutrient requirements could be supplied at planting and through maintenance fertilizers during production.
Bean and Chinese kale plant parameters at harvest typically peaked at 25% SBA, and then decreased with increasing SBA %.Adding 25% SBA to a commercial greenhouse media did benefit the seedling growth, providing additional nutrients for seedling growth, while reducing the cost of production my supplementing the more expensive greenhouse media by a readily available by-product of the sugarcane industry.Increasing the SBA % to 50% or greater is not recommend, but additional research should explore at what percentage of SBA above 25% and below 50% would still benefit seedling plant growth.

Table 3 .
Impact of sugarcane ash percentage (SBA %) on the exchangeable cations (calcium, magnesium, potassium, and sodium) for the five sugarcane bagasse ash and greenhouse media growing mixtures

Table 7 .
Impact of sugarcane bagasse ash percentage (SBA %) of growth medium on bean seedling stalk, leaves, tops, and total fresh weights (g) averaged across two experiments, four replications per experiment, and five seedlings per replication

Table 8 .
Impact of sugarcane bagasse ash percentage (SBA %) of growth medium on bean seedling oven dried weights (stalk, leaves, tops, roots and total) two experiments, four replications per experiment, and five seedlings per replication

Table 9 .
Impact of sugarcane bagasse ash (SBA) percentage of growth medium on Chinese kale fresh root weights (g) and plant establishment by experiments 1 and 2, four replications per experiment, and five seedlings per replication

Table 11 .
Impact of sugarcane bagasse ash (SBA) percentage of growth medium on Chinese kale seedling on Plants dry weights (g) averaged across two experiments, four replications per experiment, and five seedlings per replication.
Note. z Percentage of sugarcane bagasse ash (SBA) in the growth medium based on volume; y Means in a column followed by the same lower case letter are not significantly different at P ≤ 0.05, ANOVA.