How Algal Biofertilizers Can Accelerate Sustainable Agriculture

Rhykka Connelly, PhD
Research Associate
Center for Electromechanics
r.connelly@cem.utexas.edu

Until the 20th century, agricultural production, and thus population growth, was limited by the availability of plant nutrients—namely nitrogen and phosphorus. From 1909 to 1913, Carl Bosch industrialized nitrogen synthesis by reacting nitrogen gas with hydrogen gas to produce megatons of fertilizer and explosives. The fully developed system is called the Haber–Bosch process. Today, the Haber–Bosch process consumes more than one % of the energy on Earth and is responsible for feeding roughly one- third of the world’s population. Many countries have enacted policies that encourage the use of these synthetic fertilizers and other modern farming technologies to boost crop yields and keep pace with population growth. Over time, these practices have led to a number of environmental problems and ironically, diminished crop yields. Aggressive synthetic fertilizer use and tillage is credited with increased soil erosion, degrading local ecosystems that fight pests and disease, increased water demand, and stunting crop productivity. Furthermore, the production of synthetic fertilizers is dependent on fossil fuels and contributes towards greenhouse gas emissions. In response to environmental concerns, sustainable organic agriculture has become an increasingly popular option. The application of biofertilizers has been shown to decrease soil erosion, pest infestation, and water requirements, and improve soil tilth. The use of algae as a biofertilizer is particularly appealing for several reasons. Algae can be grown in arid areas that are unsuitable for traditional crops, can reclaim nutrients in waste streams, and can produce biofertilizer “crops” year round. Large scale growth of algae is accelerating and the Center for Electromechanics (CEM) at The University of Texas has developed cost-effective technologies to harvest and process algal biomass for use as animal feed or biofertilizer. CEM has been awarded a grant to harvest algae from a tertiary waste stream and assess the recovered algae as a biofertilizer on a larger scale on the UT campus in 2011-2012. Based on the data generated in our pilot study and in the literature, we predict improved soil tilth and improved plant nutrient uptake. The ultimate goal of the study is to provide the data necessary to recommend replacement of synthetic fertilizer on the UT campus with sustainable algal biofertilizer. This essay presents the challenges posed by conventional agricultural practices through a historical perspective, outlines the potential of biofertilizers as an alternative to mainstream synthetic fertilizers, and presents our current applied research at the University of Texas demonstrating a technique to use microalgae to reclaim phosphorous and nitrogen from waste water streams and redirect it for support of agricultural production.

The Rise and Impact of Synthetic Fertilizers

Illustratoin of fertilizer production routes
Fig. 01. Fertilizer Production Routes. The Haber-Bosch process converts natural gas and nitrogen from into ammonia to produce urea and commercial fertilizers. Phosphate rock is converted to usable phosphates.

Fertilizers are substances added to soil to improve its fertility, and thus, the growth and yield of plants. In the earliest times, people noted that the first yield on a plot of land qualitatively surpassed subsequent ones. Thus, there had to be a way of maintaining or even enhancing yield while staying on the same plot of land. Between 800 to 200 B.C. Greek farmers enriched their soils by applying city sewage and animal manure to their vegetable crops and olive groves.1 With time, natural fertilization became more refined to keep pace with population growth. By the 20th century, it was understood that the core plant nutrients for optimal plant growth and yield are nitrogen (N), phosphorous (P), and potassium (K). Until the 20th century, agricultural production, and thus population growth, was limited by the availability of plant nutrients— namely nitrogen and phosphorus. From 1909 to 1913, Carl Bosch industrialized nitrogen synthesis by reacting nitrogen gas from air with hydrogen gas from natural gas to produce megatons of ammonia-based fertilizer. The fully developed system is called the Haber–Bosch process. Today, the Haber–Bosch process consumes more than one % of the energy on Earth and is responsible for feeding roughly one-third of the world’s population.2 It has been called the most important technological invention in the twentieth century.3

Because of the Haber-Bosch process and other improvements, industrial agriculture has substantially increased crop yields in parallel with population growth. For example, in 1920 when the world population was ~1.65 billion, U.S. farmers produced an average of 30 bushels of corn per acre; today, the world population is ~6.5 billion and corn yields average about 134 bushels per acre, an increase of almost 350%.4 The fertilizer consumption rate in 1920 was ~6.1 million tons. One hundred years and 4.8 billion people later, the fertilizer consumption rate is estimated to reach 200 million tons.5 By 2050, global population is projected to increase by 50% and global grain demand is projected to double.6 Given synthetic fertilizer’s dependence on natural gas and rock phosphate, an alternate supply of fertilizer N:P:K will be required to meet future global food demands.

Fossil Fuel Requirements. It is estimated that one percent of the world’s energy consumption now goes toward fertilizer manufacture.7 On average, 5.5 gallons of fossil fuels per acre, per year are needed to fertilize soil for farming.8 Another way to state this is that the average U.S. farm uses three kcal of fossil energy to produce one kcal of food energy. Ironically, it is estimated that crops actually absorb only one-third to one-half of the nitrogen applied to farmland as fertilizer,9 although this %age remains controversial (Nielsen and Jensen 1986).10 The excess nutrients are free to remain in the applied soil, or they can be washed away as fertilizer run-off.

Eutrophication of Waters. One of the most dramatic illustrations of the environmental cost of excessive nitrogen fertilizer is the massive hypoxic (low dissolved oxygen) “dead zone” in the Gulf of Mexico, where runoff from the agricultural belt of the United States is concentrated by the Mississippi River system and deposited into the Gulf. High-nutrient levels stimulate algal blooms, and when the bloom subsides, subsequent decomposition by bacteria consumes dissolved oxygen deep in the water column faster than it can be replenished from the surface.11 Low oxygen levels decimate immobile bottom dwellers and drives off mobile sea life such as fish and shrimp, which further impacts organisms further up in the food change and those whose livelihoods depend on the marketing of these organisms.

The U.S. Environmental Protection Agency has blamed current farming practices for 70% of the pollution in the nation’s rivers and streams. The agency reports that runoff of chemicals, silt, and animal waste from U.S. farmland has polluted more than 173,000 miles of waterways.12 Elevated levels of nitrate and pesticides have likewise been found in shallow groundwater in more than half of the United States’ agricultural watersheds.13 Water in more than 20% of these watersheds exceeds safe drinking water standards for nitrate,14 which is a potential risk factor for cancer and reproductive problems.15

Impact on Air Quality. Nitrogen-based fertilizers contribute directly to global warming.16 Making (Haber-Bosch) and transporting one kilogram of nitrogen in a fertilizer releases 3.7 kg of carbon dioxide into the atmosphere.17 Currently, one third of N2O emissions and greater than half of the total global CH4 emissions stem from anthropogenic sources including industry, fossil fuel acquisition and use, biomass burning, and agricultural.18 The IPCC estimated that the agricultural sector contributes 65% of global anthropogenic N2O emissions, 40% of global anthropogenic CH4 emissions, and 10-12% of global anthropogenic CO2 emissions.19

Impact on Soil Tilth. Tilth refers to the physical condition of a soil, including its texture and relative ability to hold moisture and nutrients. It is a key indicator of a soil’s health. Soil in good tilth is a loamy nutrient-rich soil that has an appropriate mixture of sand, clay and organic matter that prevents severe compaction and promotes oxygen circulation. It takes more than 20 years for a centimeter of soil to form. The deterioration of soils is one of the most serious global challenges facing humankind as it attempts to feed a growing population. It has been estimated that since World War II, poor farming practices have damaged ~1.3 million acres, or about 38% of all farmland in use today.20 Chemical fertilizers decrease soil fertility by stimulating the growth of microorganisms that thrive on nitrogen. Over time, these organisms can deplete the soil of organic matter, resulting in decreased soil tilth and crop yield. Simultaneously, many beneficial microbes may be displaced by synthetic fertilizers, further resulting in poor soil formation, a lack of decomposition of nutrients, and inadequate protection from parasitic and fungal growth.21 Excess fertilizer also causes substantial accumulation of major (K+, Ca2+, Mg2+) and heavy-metal (Cd2+, Zn2+) ions in soil solutions and a decrease in soil pH, factors that may be inhibitory to plant growth.22

Transitioning to a Sustainable Agricultural Economy with Biofertilizers

Illustration of nutrient reclamation via algae

Sustainable agriculture can be defined as practices that meet current and future societal needs for food, healthy ecosystems, and healthy lives, and that do so by maximizing the net benefit to society. Additionally, sustainable agriculture also requires sustainability of energy use, manufacturing, transportation, and other economic sectors that also have significant environmental impacts. Despite the apparent unsustainability of synthetic fertilizers, it is also clear that in order to sustain the future world population, use of some form of fertilizers is necessary. Biofertilizers represent a promising alternative to synthetic fertilizers. Biofertilizers include microorganisms, such as bacteria, fungi, cyanobacteria, and algae and their metabolites that are capable of enhancing soil fertility, crop growth, and/or yield. Applying organic biofertilizers to agricultural land could increase the amount of carbon stored in these soils and contribute significantly to the reduction of greenhouse gas emissions by eliminating the requirement of fossil fuels for production through reclamation of N:P:K from wastewater streams. Furthermore, increasing organic matter in soils may cause other greenhouse gas-saving effects, such as improved workability of soils, better water retention, less production and use of mineral fertilizers and pesticides, and reduced release of nitrous oxide.23

Nutrient reclamation. Microalgae are microscopic plant-like organisms that grow suspended in nitrogen- and phosphorus-rich, CO2-fertilized water. The microalgae feed upon these suspended nutrients to promote growth and conversion of CO2 to O2. As a result, incorporating microalgal systems into conventional wastewater treatment has the potential to improve the water quality of the effluent by reducing both nitrogen and phosphorous nutrient loads into freshwater ecosystems.24 The microalgae-rich Salton Sea in Southern California is an example of a potentially very large-scale application of nutrient reclamation. Over one billion cubic meters of agricultural drainage waters flow annually into this body of water. These wastewaters contain approximately 1,000 tons of phosphate and 10-times this amount of nitrate. Nutrient removal from these drainage waters by microalgae cultures would avoid eutrophication of the Salton Sea while producing approximately 100,000 tons of microalgae biomass.25

Biofertilizer nutrient transfer to crops. It is now known that at least 16 plant- food essential elements are necessary for the growth of green plants. Green plants obtain carbon from CO2 from the air, O2 and H from water, and the remaining elements are absorbed from the soil. Plant roots take up plant-food elements from the soil in their ionic forms; potassium(K+), Calcium(Ca2+), magnesium(Mg2+), iron(Fe3+), zinc(Zn2+), nitrogen(NO-3), phosphorous( H2PO-4), sulphur(SO-4), Chlorine(Cl-), etc. Given that it is estimated that crops actually absorb only one-third to one-half of the nitrogen applied to farmland as fertilizer,26 there is a need to develop a suitable agricultural system which requires lower fertilizer input with higher fertilizer use efficiency. Recent studies by Das et. al and Rivera-Cruz et. al showed that an inoculation of a single biofertilizer significantly increased the biomass yield through increased nutrient uptake in plants.27 Both studies predicted that a lower concentration of biofertilizer would be required to produce the same yields promoted by conventional fertilizers. Neither study used algae as their biofertilizer. In fact, evidence of increased nutrient uptake from algal biofertilizers is lacking and is currently being investigated by the University of Texas.

Soil stability. Land degradation due to accelerated erosion is a serious global issue because soil resources of the world are finite and nonrenewable in the human- time scale. In general, background erosion removes soil at roughly the same rate as soil is formed. But “accelerated” soil erosion—loss of soil at a much faster rate than it is formed—is a far more recent problem primarily due to aggressive agricultural practices. There are different methods of reducing soil erosion, including contour tillage or no-tillage, installing windbreaks, and leaving processed crops on the field. Interestingly, microalgae may also participate in the reduction of soil erosion by contributing soil- binding polysaccharides from their cell walls.28 The long-term influence of polysaccharides on aggregate stability may result from microbial mineralization of extracellular polysaccharides.29 Bailey et al.30 found that microalgae-supplemented soil significantly increased the %age of soil aggregates after six weeks of incubation as compared to soil without algae. These data, together with the prediction that lower amounts of biofertilizers are required for equivalent nutrient uptake by crops, may mean that soil erosion and consequent nutrient run-off may be much reduced through the use of algal biofertilizers.

To date, many studies have shown that biofertilizers have numerous benefits to soil quality and crop yield:

  • increased nutrient transfer,31
  • comparable crop yield,32
  • increased beneficial microorganisms,33
  • stabilization of soil aggregates,34 and
  • decreased reliance on fossil fuels.35

Currently, data characterizing the use of microalgae as a biofertilizer is lacking. However, individual reports suggest that microalgae could represent a promising alternative to commercial, or alternative organic fertilizers:

  • Microalgae have been shown to efficiently recycle N:P:K nutrients from wastewater streams36 and stabilize soil aggregates37;
  • Microalgae can be grown in environments that cannot support traditional land-based crops and therefore do not displace those crops;
  • The production of microalgae, if coupled to a wastewater stream, requires no fossil fuel inputs;
  • Algae can convert waste CO2 to O2; and
  • Our pilot study using processed microalgae as a biofertilizer showed that crop yield exceeded that of chemical fertilizer applied at the same rate.

Taken together, the University of Texas Algae Processing Program believes that microalgae may hold an important place in the future of agriculture. UTAPP has designed study to harness the power of microalgae as a biofertilizer on the UT campus. The study will be conducted over the 2011-2012 season and is outlined in more detail below.

Replacement of Traditional Fertilizers with Processed Algal Biomass on the UT Campus

UT has developed and deployed an end-to-end algal biomass processing solution that recovers algal lipids and produces clean biomass suitable for use as animal/aquacultural feeds or biofertilizers. UT has partnered with the City of Austin Wastewater Utility at Hornsby Bend to harvest microalgae from their water polishing ponds to yield algal oils and clean biomass. In this process, the UT-developed mobile processing unit extracts algal water, separates the algae from the water, ruptures the algal cells, then recovers the oil, all without the use of harmful chemicals and solvents. This means that the processed (de- oiled) biomass is clean and rich with proteins and nutrients suitable for use as a biofertilizer.

UT has conducted a preliminary study examining the effects of processed biomass on crop yields. The beds were conditioned with either 12.5 kg/acre dried Chlorella sp. biomass,38 or with an identical concentration of commercial fertilizer (positive control). A third unfertilized garden bed was established as a negative control. Each bed contained six cherry tomato plants and six herb plants. Soil analyses were conducted prior to and after soil fertilization. The data showed that the algal-fertilized crops grew 21% taller, and yielded 25% more produce than plants in the control beds. These data, suggest that processed Chlorella sp. improves crop production compared to a commercially available inorganic fertilizer.

Satellite views of the JJ Pickle Research Campus
Google Satellite view of the JJ Pickle Research Campus (left) and the proposed site of the fertilizer plots located on the Pickle Campus (right).

A larger scale algal biofertilizer project supported by the UT Sustainability Initiative is commencing this fall. For this demonstration, nutrient-enriched algae from the Water Utility at Hornsby Bend’s ponds was processed using UT technologies. The processed biomass has been analyzed for nitrogen and phosphorus content. Algae-conditioned plots will be compared to plots conditioned with the comparable amount of traditional fertilizer. The results will be reported to the Sustainability Office and the wider community. We expect improved soil conditions and plant health at a fraction of the cost of the traditional fertilizer.

Our larger scale demonstration with rigorous testing parameters serves as a first step to replace unsustainable inorganic fertilizers with a system wherein algae efficiently recovers waste nitrogen and phosphorus for re-use in agricultural production, thereby mitigating environmental and economical issues facing the agricultural industry.

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