c-ray
02-05-2007, 07:33 AM
from http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/opp10736
Evaluation of greenhouse substrates containing zeolite and secondary use of spent substrate
This work is a result of comprehensive four-year study on greenhouse substrates conducted at CDC South, Brooks, Alberta.
Neutral substrates used in soilless culture can remarkably differ in their physical properties. These physical properties affect the air content and retained volume of available water in the substrate.These differences need to be taken into consideration when growing greenhouse crops with varying demands for water and oxygen in the root zone.
Sawdust has been the standard growing medium for the greenhouse industry in Alberta for several decades. This is because of its low cost and relatively high plant/fruit productivity. However, sawdust is prone to gradual decomposition (Maas and Adamson 1972). Decomposition leads to unfavorable substrate physical properties converting it from a "dry" to "wet" substrate with a higher volume of retained water and a deficiency of available oxygen.
Coir is more resistant to degradation as it contains 2-3 times more lignin, a highly stable polyphenolic compound. Rockwool and perlite are not degraded by microorganisms due to their mineral nature. Unfortunately, both of these substrates are more expensive.
The high environmental cost of inorganic substrate disposal is one issue facing the greenhouse industry. On the other hand, the recycling of organic substrates in agricultural operations and land reclamation can be easily achieved.
Despite perlite’s (Westgro) higher stability, there was no improvement in productivity found for bell pepper or long English cucumber when compared to sawdust. During experiments in 2001/2002 and 2002/2003, consistently lower yields of perlite-grown, long English cucumber were observed. There was a 9.7% yield decrease in the spring crop of long English cucumber, cv. Sabrina, in 2001/2002. In 2002/2003, very similar results with a 10.3% decrease in yield of the spring crop and 9.9% decrease in the summer crop, respectively. Since bell pepper is better adapted to "dry" substrates than cucumber, this effect of perlite was less evident. The plants productivity was restored when 20% zeolite was added to the perlite. Since perlite is a "dry substrate" with a steep water retention curve, perlite-zeolite mixtures will be preferable for some crops. Zeolite shows a remarkable water retention capacity (Mondale, Mumpton, and Aplan 1987; Bohme 1995; Mumpton 1999). More frequent irrigation rates may also be necessary when perlite is used as a greenhouse substrate for plants with a demand for high moisture levels in the substrate, like long English cucumbers.
Bell pepper showed varietal differences in response to coir (Millenniumsoil Coir). Although there was some encouraging results with coconut fiber for orange pepper production in 2002/2003 and 2003/2004 compared to the control, there was a consistently negative effect for yellow pepper variety, cv. Sardana, the same years. Red pepper showed both positive and negative responses. Increasing the air content of coir by increasing particle size will increase air volume and make it more suitable for bell peppers production.
Coir had no negative effect on the production of long English cucumbers during all three years of the experiments. Yield of the coir-grown fall crop increased by 11.9% (2002/2003) and 12.4% (2003/2004) compared to sawdust. Compared to sawdust, coir, with a flatter water retention curve, appears to be the most appropriate substrate for long English cucumber.
Rockwool (Grodan, Denmark) was used in 2003/2004. Rockwool was a superior greenhouse substrate for most treatments and all three crops used in the experiments with the exception of yellow peppers, cv. Sardana, which showed similar negative response as with coir. The yield of cv. Sardana decreased by 19.8% and 22.7% when grown on rockwool with and without supplemental CO2. Rockwool and coir, exhibit the physical properties of a "wet" substrate, with a higher water retention capacity and lower air content, cv. Sardana, seems to have a higher demand for an oxygen supply in the root zone. This can also be supported by the results of trials conducted with bell peppers in 2002/2003, cv. Sardana performed better on perlite, a "dry" substrate, than coir when grown at two levels of CO2.
There was an interaction between enriched CO2 and substrate treatments. Bell pepper grown on sawdust consistently demonstrated a higher response to CO2 compared to the plants grown on coir. The yield of sawdust-grown pepper plants, with supplemental CO2 increased by 22.0% (2002/2003) and 22.2% (2003/2004). Yield was increased in coir-grown plants by 17.2% and 15.9% in during the same period. Yield from plants grown on perlite with enriched CO2 was inconsistent from year to year. The lowest response was observed in 2001/2002 (18.1%) and highest response in 2002/2003 (36.7%). The sawdust-grown long English cucumber plants were more responsive to enriched CO2 than coir-grown plants.
Zeolites are a group of naturally occurring minerals with physical and physiochemical properties that can be used in such diverse areas as construction and agriculture. Zeolites are capable of adsorbing part of the excess nutrients, resulting in more balanced macronutrient cation ratios in the root environment (Savvas, Samantouros, Paralemos, Vlachakos, Stamatakis, and Vassilatos 2004). Four years of experiments with zeolite amendments at CDC South in Brooks allowed for the reproduction of the positive effect of zeolite mixtures on all three greenhouse crops. However, this effect depended on the crop, variety, zeolite grow bag content, zeolite source, environmental conditions (with and without CO2), and substrate type. There was also a negative effect of zeolite on horticultural crops under some of the trial conditions.
The type of substrate used strongly determined the effect of the zeolite. Sawdust-zeolite mixtures showed most consistent effect on bell pepper production, increasing yields by 5%-20%. Nineteen treatments out of 24 showed a positive effect on pepper productivity with sawdust containing a zeolite content of 10% and 20%. The effect of zeolite amendments to perlite and coir on pepper productivity was less consistent. Perlite-zeolite mixtures were beneficial in 8 of 18 treatments only. Coir-zeolite mixtures improved yield in only 3 of 12 treatments, not having any effect on the bell pepper in most treatments. Nevertheless, the highest response of pepper plants to zeolite was associated with perlite and coir. Perlite-zeolite mixture, 20% zeolite, increased the yield of yellow pepper cv. Bossanova, by 41% in 2001/2002 and coir-zeolite mixture increased yield of orange pepper cv. Sympathy, by 30.1% in 2002/2003. Both treatments included enriched CO2. Increasing zeolite content in the growing medium to 40% did not lead to a yield increase in bell peppers.
The spring crop of long English cucumbers, cv. Sabrina, was most responsive to the zeolite treatments regardless of what substrate was used when compared to the summer crop, cv. Flamingo, and the fall crop, cv. Korinda. However, the effect was less pronounced when compared to bell peppers with the maximum effect of 11.6% versus 41.0% for long English cucumbers and bell peppers respectively. There were only 9 out of 28 treatments where zeolite had a positive effect.
The excessive application of zeolites pushing buffering capacity of the neutral substrate too high, benefited neither bell peppers or long English cucumbers. This trend was confirmed in the 2004/2005 experiment when 15% zeolite #2 was used with long English cucumbers. Zeolite #2 had one of the highest Cation Exchange Capacity (CEC) reported in literature (202 meq). The effect was dependent on the substrate used with the zeolite. Cucumber yields decreased by 13.9% and 14.5% with zeolite #2 in coir mixtures grown without and with supplemental CO2 respectively compared to pure coir. The yield of the crop grown on sawdust-zeolite mixture was increased under both CO2 levels. The buffering capacity of coir might have aggravated the negative effect of zeolite on productivity of long English cucumbers in this case.
Application of zeolite for the production of beefsteak tomato indicated a trend of increasing yield when used as a 10% amendment with sawdust and coir. However, one year of the experiments did not provide conclusive evidence of the positive effect of zeolite on tomato production.
The positive effect of zeolite on greenhouse crops may be explained by the retention of nutrients during the day feeding period and their gradual release during night period. This is when no nutrients are provided to the plants through irrigation system, leading to more uniform nutrient supply. Another explanation may relate to high water retaining capacity of zeolite, which may benefit mixtures of zeolite with "dry" substrates like sawdust and perlite. If this is the case, zeolite benefits will be less evident in mixtures of zeolite with "wet" substrates, which possess higher CEC. Coir is a typical example a "wet" substrate. Coir showed no superior results in mixtures with zeolite in this study. However, the effect of other factors such as mineral composition of zeolite on crop productivity cannot be ruled out. Therefore, the precise mechanism of zeolite effect on greenhouse crops requires further investigation.
There was no interaction effect between zeolite amendments and enriched CO2 observed in this study.
Four years of test trials with zeolites allowed for the accumulation of unique information about the effect of zeolites on three major greenhouse crops. Zeolite amendments to sawdust produced most consistent positive effect on crop yield. The use of zeolite with perlite and coir should be considered in combination with the specific crop response, which can vary depending on environmental factors, such as CO2 level and the genetic factor of the plant.
In this study beefsteak tomato plants grown on substrates with different buffering capacity, were subjected to 8 hours of acidity stress. This clearly demonstrated that as little as 10% zeolite in the substrate with moderate 99 meq CEC could provide plants with an effective protection during a short period of severe stress. The best result was achieved for the combination coir-zeolite where almost 100% plant had occurred on day 2 after the acidity treatment. Pure coir was also effective in crop protection against acidity stress. However, the same level of recovery was achieved only on day 7 of the stress treatment. The substrates with a high buffering capacity could also protect crops against short period of salinity stress.
Although disease assessments were not part of this study, mixtures containing zeolite as greenhouse media may significantly decrease the risk of crop loss due to root exposure to extreme conditions of acidity (and salinity) stress. Since 10% zeolite can be added to the substrate for only a fraction of the substrate cost, using zeolite mixtures instead of pure substrate might mitigate potential risk associated with nutritional problems. The application of zeolites for risk management has not reported in the literature previously.
Every year Alberta greenhouse growers pay for the disposal of thousands of bags of used substrate. There is an environmental concern when damping large amount of waste every year too. If a cost-effective process is developed to convert used growing media into a commercial product that can be marketed as a high quality topsoil and soil conditioner both these issues can be addressed. Growers will see an increase in profitability margins through elimination of waste storage and disposal costs and provide an additional revenue source from direct sales of the recycled product.
In the trial with nursery crops, spent greenhouse substrate may create better conditions for root development than a standard mixture currently used in the industry. The productivity of Ribes alpinum, an ornamental shrub popular in North America, increased more than 2 times in some of the treatments when using spent greenhouse substrates. Spent coir-based mixtures were more effective for nursery crop production than spent sawdust-based mixtures. However, in both cases there was an increase in productivity compared to the standard growing medium, based on bark, peat, and sand. The yields were improved by 40.4%-76.7% and by 50.9%-143.5% for spent sawdust-based and spent coir-based substrates respectively. The combination of sawdust-zeolite was beneficial, although the yield increase was minor compared to pure sawdust. The yield of the crop was improved by 4.2%. There was no positive effect observed when spent sawdust/zeolite-containing substrates were used in combination with peat and sand nor was the combination of zeolite and coir beneficial for the shrub production. Coir-zeolite mixture led to 12.1% decrease in productivity of Ribes alpinum compared to pure coir, which confirmed many observations in experiments with greenhouse crops.
Spent greenhouse substrates can be successfully used for the production of other horticultural crops. Moreover, the spent substrates considerably exceeded the efficiency of the standard mixture.
The findings in this study create an opportunity for the development of new market of highly efficient horticultural substrates based on spent greenhouse media.
Evaluation of greenhouse substrates containing zeolite and secondary use of spent substrate
This work is a result of comprehensive four-year study on greenhouse substrates conducted at CDC South, Brooks, Alberta.
Neutral substrates used in soilless culture can remarkably differ in their physical properties. These physical properties affect the air content and retained volume of available water in the substrate.These differences need to be taken into consideration when growing greenhouse crops with varying demands for water and oxygen in the root zone.
Sawdust has been the standard growing medium for the greenhouse industry in Alberta for several decades. This is because of its low cost and relatively high plant/fruit productivity. However, sawdust is prone to gradual decomposition (Maas and Adamson 1972). Decomposition leads to unfavorable substrate physical properties converting it from a "dry" to "wet" substrate with a higher volume of retained water and a deficiency of available oxygen.
Coir is more resistant to degradation as it contains 2-3 times more lignin, a highly stable polyphenolic compound. Rockwool and perlite are not degraded by microorganisms due to their mineral nature. Unfortunately, both of these substrates are more expensive.
The high environmental cost of inorganic substrate disposal is one issue facing the greenhouse industry. On the other hand, the recycling of organic substrates in agricultural operations and land reclamation can be easily achieved.
Despite perlite’s (Westgro) higher stability, there was no improvement in productivity found for bell pepper or long English cucumber when compared to sawdust. During experiments in 2001/2002 and 2002/2003, consistently lower yields of perlite-grown, long English cucumber were observed. There was a 9.7% yield decrease in the spring crop of long English cucumber, cv. Sabrina, in 2001/2002. In 2002/2003, very similar results with a 10.3% decrease in yield of the spring crop and 9.9% decrease in the summer crop, respectively. Since bell pepper is better adapted to "dry" substrates than cucumber, this effect of perlite was less evident. The plants productivity was restored when 20% zeolite was added to the perlite. Since perlite is a "dry substrate" with a steep water retention curve, perlite-zeolite mixtures will be preferable for some crops. Zeolite shows a remarkable water retention capacity (Mondale, Mumpton, and Aplan 1987; Bohme 1995; Mumpton 1999). More frequent irrigation rates may also be necessary when perlite is used as a greenhouse substrate for plants with a demand for high moisture levels in the substrate, like long English cucumbers.
Bell pepper showed varietal differences in response to coir (Millenniumsoil Coir). Although there was some encouraging results with coconut fiber for orange pepper production in 2002/2003 and 2003/2004 compared to the control, there was a consistently negative effect for yellow pepper variety, cv. Sardana, the same years. Red pepper showed both positive and negative responses. Increasing the air content of coir by increasing particle size will increase air volume and make it more suitable for bell peppers production.
Coir had no negative effect on the production of long English cucumbers during all three years of the experiments. Yield of the coir-grown fall crop increased by 11.9% (2002/2003) and 12.4% (2003/2004) compared to sawdust. Compared to sawdust, coir, with a flatter water retention curve, appears to be the most appropriate substrate for long English cucumber.
Rockwool (Grodan, Denmark) was used in 2003/2004. Rockwool was a superior greenhouse substrate for most treatments and all three crops used in the experiments with the exception of yellow peppers, cv. Sardana, which showed similar negative response as with coir. The yield of cv. Sardana decreased by 19.8% and 22.7% when grown on rockwool with and without supplemental CO2. Rockwool and coir, exhibit the physical properties of a "wet" substrate, with a higher water retention capacity and lower air content, cv. Sardana, seems to have a higher demand for an oxygen supply in the root zone. This can also be supported by the results of trials conducted with bell peppers in 2002/2003, cv. Sardana performed better on perlite, a "dry" substrate, than coir when grown at two levels of CO2.
There was an interaction between enriched CO2 and substrate treatments. Bell pepper grown on sawdust consistently demonstrated a higher response to CO2 compared to the plants grown on coir. The yield of sawdust-grown pepper plants, with supplemental CO2 increased by 22.0% (2002/2003) and 22.2% (2003/2004). Yield was increased in coir-grown plants by 17.2% and 15.9% in during the same period. Yield from plants grown on perlite with enriched CO2 was inconsistent from year to year. The lowest response was observed in 2001/2002 (18.1%) and highest response in 2002/2003 (36.7%). The sawdust-grown long English cucumber plants were more responsive to enriched CO2 than coir-grown plants.
Zeolites are a group of naturally occurring minerals with physical and physiochemical properties that can be used in such diverse areas as construction and agriculture. Zeolites are capable of adsorbing part of the excess nutrients, resulting in more balanced macronutrient cation ratios in the root environment (Savvas, Samantouros, Paralemos, Vlachakos, Stamatakis, and Vassilatos 2004). Four years of experiments with zeolite amendments at CDC South in Brooks allowed for the reproduction of the positive effect of zeolite mixtures on all three greenhouse crops. However, this effect depended on the crop, variety, zeolite grow bag content, zeolite source, environmental conditions (with and without CO2), and substrate type. There was also a negative effect of zeolite on horticultural crops under some of the trial conditions.
The type of substrate used strongly determined the effect of the zeolite. Sawdust-zeolite mixtures showed most consistent effect on bell pepper production, increasing yields by 5%-20%. Nineteen treatments out of 24 showed a positive effect on pepper productivity with sawdust containing a zeolite content of 10% and 20%. The effect of zeolite amendments to perlite and coir on pepper productivity was less consistent. Perlite-zeolite mixtures were beneficial in 8 of 18 treatments only. Coir-zeolite mixtures improved yield in only 3 of 12 treatments, not having any effect on the bell pepper in most treatments. Nevertheless, the highest response of pepper plants to zeolite was associated with perlite and coir. Perlite-zeolite mixture, 20% zeolite, increased the yield of yellow pepper cv. Bossanova, by 41% in 2001/2002 and coir-zeolite mixture increased yield of orange pepper cv. Sympathy, by 30.1% in 2002/2003. Both treatments included enriched CO2. Increasing zeolite content in the growing medium to 40% did not lead to a yield increase in bell peppers.
The spring crop of long English cucumbers, cv. Sabrina, was most responsive to the zeolite treatments regardless of what substrate was used when compared to the summer crop, cv. Flamingo, and the fall crop, cv. Korinda. However, the effect was less pronounced when compared to bell peppers with the maximum effect of 11.6% versus 41.0% for long English cucumbers and bell peppers respectively. There were only 9 out of 28 treatments where zeolite had a positive effect.
The excessive application of zeolites pushing buffering capacity of the neutral substrate too high, benefited neither bell peppers or long English cucumbers. This trend was confirmed in the 2004/2005 experiment when 15% zeolite #2 was used with long English cucumbers. Zeolite #2 had one of the highest Cation Exchange Capacity (CEC) reported in literature (202 meq). The effect was dependent on the substrate used with the zeolite. Cucumber yields decreased by 13.9% and 14.5% with zeolite #2 in coir mixtures grown without and with supplemental CO2 respectively compared to pure coir. The yield of the crop grown on sawdust-zeolite mixture was increased under both CO2 levels. The buffering capacity of coir might have aggravated the negative effect of zeolite on productivity of long English cucumbers in this case.
Application of zeolite for the production of beefsteak tomato indicated a trend of increasing yield when used as a 10% amendment with sawdust and coir. However, one year of the experiments did not provide conclusive evidence of the positive effect of zeolite on tomato production.
The positive effect of zeolite on greenhouse crops may be explained by the retention of nutrients during the day feeding period and their gradual release during night period. This is when no nutrients are provided to the plants through irrigation system, leading to more uniform nutrient supply. Another explanation may relate to high water retaining capacity of zeolite, which may benefit mixtures of zeolite with "dry" substrates like sawdust and perlite. If this is the case, zeolite benefits will be less evident in mixtures of zeolite with "wet" substrates, which possess higher CEC. Coir is a typical example a "wet" substrate. Coir showed no superior results in mixtures with zeolite in this study. However, the effect of other factors such as mineral composition of zeolite on crop productivity cannot be ruled out. Therefore, the precise mechanism of zeolite effect on greenhouse crops requires further investigation.
There was no interaction effect between zeolite amendments and enriched CO2 observed in this study.
Four years of test trials with zeolites allowed for the accumulation of unique information about the effect of zeolites on three major greenhouse crops. Zeolite amendments to sawdust produced most consistent positive effect on crop yield. The use of zeolite with perlite and coir should be considered in combination with the specific crop response, which can vary depending on environmental factors, such as CO2 level and the genetic factor of the plant.
In this study beefsteak tomato plants grown on substrates with different buffering capacity, were subjected to 8 hours of acidity stress. This clearly demonstrated that as little as 10% zeolite in the substrate with moderate 99 meq CEC could provide plants with an effective protection during a short period of severe stress. The best result was achieved for the combination coir-zeolite where almost 100% plant had occurred on day 2 after the acidity treatment. Pure coir was also effective in crop protection against acidity stress. However, the same level of recovery was achieved only on day 7 of the stress treatment. The substrates with a high buffering capacity could also protect crops against short period of salinity stress.
Although disease assessments were not part of this study, mixtures containing zeolite as greenhouse media may significantly decrease the risk of crop loss due to root exposure to extreme conditions of acidity (and salinity) stress. Since 10% zeolite can be added to the substrate for only a fraction of the substrate cost, using zeolite mixtures instead of pure substrate might mitigate potential risk associated with nutritional problems. The application of zeolites for risk management has not reported in the literature previously.
Every year Alberta greenhouse growers pay for the disposal of thousands of bags of used substrate. There is an environmental concern when damping large amount of waste every year too. If a cost-effective process is developed to convert used growing media into a commercial product that can be marketed as a high quality topsoil and soil conditioner both these issues can be addressed. Growers will see an increase in profitability margins through elimination of waste storage and disposal costs and provide an additional revenue source from direct sales of the recycled product.
In the trial with nursery crops, spent greenhouse substrate may create better conditions for root development than a standard mixture currently used in the industry. The productivity of Ribes alpinum, an ornamental shrub popular in North America, increased more than 2 times in some of the treatments when using spent greenhouse substrates. Spent coir-based mixtures were more effective for nursery crop production than spent sawdust-based mixtures. However, in both cases there was an increase in productivity compared to the standard growing medium, based on bark, peat, and sand. The yields were improved by 40.4%-76.7% and by 50.9%-143.5% for spent sawdust-based and spent coir-based substrates respectively. The combination of sawdust-zeolite was beneficial, although the yield increase was minor compared to pure sawdust. The yield of the crop was improved by 4.2%. There was no positive effect observed when spent sawdust/zeolite-containing substrates were used in combination with peat and sand nor was the combination of zeolite and coir beneficial for the shrub production. Coir-zeolite mixture led to 12.1% decrease in productivity of Ribes alpinum compared to pure coir, which confirmed many observations in experiments with greenhouse crops.
Spent greenhouse substrates can be successfully used for the production of other horticultural crops. Moreover, the spent substrates considerably exceeded the efficiency of the standard mixture.
The findings in this study create an opportunity for the development of new market of highly efficient horticultural substrates based on spent greenhouse media.