Biomimicry
for shaping future
Agriculture
The translation to a design
1. Multilayer buffer strips
Riparian zones manage nutrients cycling in a very effective way; they provide valuable ecosystem services such as filtration of the sediments and polluting compounds, stabilization of the soil, and hosting biodiversity. When applying this system to agriculture we can successfully reduce the impact of agriculture on nutrients cycles. Problems like excessive surface and subsurface runoff carrying away nutrients can be remediated, thereby improving the water quality of the adjacent water streams. We can translate this solution taken from nature to a smaller scale, by establishing a system similar to riparian zones around the fields. The functions of the riparian habitat are mimicked by setting up a buffer zone with indigenous species with similar functional qualities and that also provide ecosystem services. The buffer zone includes a multi-layer canopy and a stratified root system to provide different niches and shading levels, diverse vegetation with various rooting depths and nutrient bioaccumulating species.
Vegetation composition of the Multilayer buffer strip
Field margins and riparian zones often consist of several components such as watercourses, banks, woodlands. This means that a range of plant communities are present: from a grassland community to shrub, woodland and aquatic communities. These have to fulfill certain functions per zone to perform optimally, as well as be native to the area. Choosing the specific species that make up the buffer strips is therefore highly dependent on the location. If streams or ditches are present around the agricultural field, aquatic communities can be included, otherwise other communities can be chosen.
Reports on effectiveness of sediment reduction have pointed out that the first buffer zone consisting of grass species, should have a width of at least 3 m to reduce up to 77% of the sediment (Lee et al., 1999). De Snoo (1998) reported that pesticide drift through the air is decreased by 95% over a distance of 3 m.
A possible setup of a buffer zone in eastern Europe would look like indicated in the following table, assuming an agricultural field growing potatoes. It is important to design the buffer zones based on local conditions. Different agricultural areas with different crops and soils have different needs. Widths, layers and species must therefore be tuned to local properties.
Environmental advantages
The strip of vegetation around the fields decreases and filters the surface runoff and sediments before it reaches the closest stream. This works physically by decreasing the velocity of the runoff. It causes the water to infiltrate and the sediment to settle. Furthermore, it works chemically by fixing the nutrients from the runoff water within the vegetation. Also, leached nutrients from the soil surface closeby the riparian zone can be taken up by deep-rooted vegetation (Jobbágy and Jackson, 2001). Next to that, functions such as hosting above and belowground biodiversity and stabilising soil will be achieved. Some vegetation of this natural boundary can serve as a crop and be productive, while other nutrient-bioaccumulating species can be used as mulch on the adjacent agricultural field (Barrios and Cobo, 2004). Natural pest control is an additional service; species in the border area can be chosen in order to attract natural enemies that feed on the pest species of the field. Furthermore, the species can stimulate a fungal-based energy channel that slows down and promotes nutrient cycling (De Vries et al., 2013). Additionally, mycorrhizal associations are stimulated that enhance macroaggregate formation and P uptake in the plant from deeper soils (Rillig and Mummey, 2006). Besides another environmental service of buffer strips is wind protection. Wind can damage crops directly, through mechanical damage and through increased erosion, and indirectly by stimulating transpiration and altering growth rates (Cleugh et al. 1998). The line of vegetation around the field will decrease the wind flow and thus reduce its impact. The buffer can further acts as a connection between natural areas, allowing species to migrate (Pascual-Hortal and Saura, 2006). Flowering species used in the first layer of the buffer may also enhance the aesthetic value and contribute to pollination of the agricultural field (Tilman et al. 2002). With the multilayer buffer strips, we promote several eco-services within one system, just as nature does.
2. Water filtration and nutrient recovering
Roots and kidneys are efficient in selectively taking up nutrients. For agriculture, constant replenishment of nutrients in the soil is needed to ensure high production levels. Although all nutrients are needed for the optimal plant development (Whiting, 2014) this part of the project focuses on the three most important ones: nitrogen (N), phosphorus (P) and potassium (K) (Barak, 2015). Modern fertilizers are based on labile compounds of these elements (ammonia based, soluble phosphate salts, potash), but they quickly leach. In order to catch those nutrients again before they leave the agricultural system, it is important to know how the different compounds behave, so an adequate filtration and recovering process can be implemented.
Nitrate (NO3-) is the form of nitrogen that is susceptible to leaching, although the major form in waste water is ammonia (NH4+ or NH3). Nitrate is a negatively charged ion, so it does not bind well to soil particles. Eluviation water moves nitrate below the root zone and drains either into the groundwater or surface water (USDA 2015, Lamb et al. 2014). Phosphorus exists as phosphate (PO43-) in soil and water systems. It can be lost mainly through soil erosion and to a lesser extent through water runoff or groundwater as it is less soluble than nitrate. Although its displacement is slow it can be increased by heavy rainfall or irrigation. It can be adsorbed to soil particles and transported by sediments and washed away to rivers and lakes (Lamb et al., 2014). Although 90-98% of the total soil potassium is in a crystalline-insoluble form, unavailable for plants, a part is present as the soluble cation K+, that can be directly taken up by the crops (Agrow Australia, 2015, Rehm and Schmitt, 2002).
Filtration processes
To increase the overall nutrient cycle in crop production a system – of selective nutrient recovering and re-application– is proposed. The way industrialized agriculture is managed can be re-adapted into a more circular dynamic, just like undisturbed ecosystems. Depending on the scale it can be established at farm level (pumping the groundwater or adjacent stream water charged with nutrients) or within an arrangement of farms (collecting the water from the local or common groundwater and streams). After collection the water passes through different phases: physical filtration (removal of big particles like sand or decayed biomass), biological filtration (removal of pollutants using microorganisms) and chemical filtration (removal of toxic or unwanted compounds). Different technologies allow for a selective recovery of nutrients such as the Filtration Assisted Crystallization Technology or FACT, developed by TNO (TNO, 2015). In this way phosphates and potassium can be crystallized and recovered from the water. In the case of nitrogen, the ammonia can be reconverted into nitrates through a nitrification process in a bioreactor (using nitrifying bacteria) (Coburn, 2015). To concentrate the solutions with the recovered nutrients semipermeable membranes can be used, as is happening in nephrons. Forward osmosis (FO) membranes is an innovative technology developed by the USA-based company HTI, being very efficient in terms of energy use (Wicaksana et al., 2011; Htiwater.com, 2015). The recovered nutrients can be directly reapplied on the fields or be further processed into more stable chemical compounds, so at the end the nutrients are recycled and do not disappear into non-usable forms as water pollutants.
Environmental advantages
The advantages of such a processing system are the following: nutrients that would be lost are recovered and are re-used for crop production. Enhancing the efficiency of nutrient cycling within the agricultural area (individual or several farms) increases the fertility of the soil as the nutrients remain longer in the same place and do not leach. Furthermore, farmers are less dependent on the purchase of fertilizers. The current dynamic of industrialized agriculture relies on the intensive use of external inputs, with the constant manufacturing of artificial nutrients. The cycling allows the farmers to re-use the already purchased fertilizers and limit their loss. Additionally, risks of water pollution and eutrophication are decreased. After the filtration and nutrient recovering the water released is cleaner (it has a lower concentration of nutrients and pollutants), so the environmental footprint in the watersheds is reduced.
