Urine in crop production proves key to sustainability in developing countries.
In a comprehensive landmark study the Stockholm Environment Institute has defined the characteristics, economic value, application strategies and handling protocols for the use of urine in crop production. Their evidence is based on research and practical experiences in India, Africa, Europe and Central America. A comprehensive review of this research as it applies to re-circulating water systems will be offered in upcoming Bioponica® workshops and in system operation manuals.
Once consumed, plant nutrients leave the body as excreta. If all the consumed foods were recycled as waste to the original cultivation source, the fertility of the arable land or bioponic system is assured. Through source separation and safe handling urine may be captured and stored for small and large scale operations. Urine contains most macronutrients and micronutrients excreted in our waste, including nitrogen, phosphorus and sulfur in plant available forms. Urine fertilized crops show no statistical difference in yield when compared to mineral fertilized crops.
Urine is a well balanced nitrogen-rich liquid fertilizer. The average volume ranges from 0.8-1.5liters per day. The concentration of nutrients depends on food intake. Typically there are 3-7grams of nitrogen per liter. In comparison to mineral fertilizers, urine phosphorus provides a plant–available form, making this particularly important, as finite limitations of mineral phosphates place the agriculture industry in vulnerable ‘peak ‘phosphate’ situation. Due to the high ratios of nitrogen:phosphorus and nitrogen:potassium urine may be added to plants at rates greater than typical for nitrogen so long as salinity is monitored. Otherwise, in bioponic systems, pH adjusted growth media supplemented with phosphorus and postassium rich biochar is advisable.
Typically plants performed best when urine is applied at a rate of 0.4-0.6 liters per plant or, with lettuces, 1 liter per square meter of growing area. In-ground applications were best when given at 2 and 4 week intervals after germination. There is no standard for dilution of urine - either neat or diluted application was not a factor. Excessive application was not found to be harmful in the pre-fruiting stages and proved beneficial even when used a rate of 6 liters per plant or per square meter when working with phosphate deficient soils. It is not recommended to apply during plant fruiting or generative stages when nutrient uptake declines. Plants with small root systems including beets, carrots, lettuces and onions can benefit from application throughout cultivation time.
Handling and Storage:
Urine itself is typically sterile, particularly when a clean catch collection method is employed. However in large scale operations pathogen exposure may occur from fecal cross-contamination or from unsanitary handling. To mitigate risk, the W.H.O. has established effective barriers for safe use of urine in agriculture. A nine step Barrier Method limits risk from even the most pathogenic organisms and includes protocols for source separation, storage, application, crop restriction, withholding period, protective equipment, hand washing, health and hygiene promotion, food handling and cooking.
When fed to the garden plants immediately, urine presents little risk but most larger operations utilize storage containers and toilet separation designs that carry risk. For effective control, storage for a period of 1-6 months causes most enteric pathogens to die off, due to the high pH diluted urine at around 8.8. By withholding application of urine to crops for one month prior to cultivation, risk is further reduced to negligible levels.
As another sanitation approach, an ongoing Phillipines project, Terra Perta Sanitation, is testing the introduction of microbes to the urine container prior to storage. This is done in the form of vermicompost, which causes a fermentation plus combination with biochar. This method, taken from ancient Aztec ‘black soil’ studies, prevents the bacterial urease process which hydrolyses urea into ammonia and bicarbonate; something that happens during storage. Added benefits include less volatile ammonia buildup and less smell.
There are exceptions to stringent protocols when farms utilize urine from a small family, as cross contamination is negligible in comparison to person to person exposure. Likewise, when clean handled urine is used directly from source to soil, pathogenesis is rare. With bioponics, similar handling and storage protocols must be evaluated. As an added safeguard, the natural microbial breakdown process of ammonia through nitrification provides an additional barrier to risk. In all cases, plant leaf or fruit urine exposure should not occur and when root crops are involved or with foods eaten raw. Unless it is shown that nitrification remediates in a shorter period, or else urine is decomposed in algae raceways, withholding of urine during last month of cultivation should be the practiced.
The benefits of urine-fertilization are immense in communities that are challenged economically to afford mineral fertilizers. As well, the self sufficiency created is a model for all farmers in years to come as fuel prices, ‘peak phoshate’, and nutrient depletion through municipal waste disposal are an impending constraint to food production worldwide.