A Comparison of Conventional and Granular Manure Organic Fertilizers

During the recent decade, organic farming has gained increasing interest as an environmentally friendly production system because of its positive effects on the environment.  While many investigations have focused on the conversion to organic forms of fertilizer, some studies involving organically derived nutrients have suggested a level of discrepancy between nitrogen (N) losses (via leaching and volatilization) and the subsequent availability of N to plants.  The general intent of this effort involves a relative comparison of conventional fertility management schemes with a heat treated granular manure product (EarthRenew, Inc.).  During the first year (2009), research was devoted to establishing nutrient and plant development baselines, based solely on preplant applications of the granular manure product at planting.  Evaluations of overall nutrient persistence using soil or plant tissue nutrient and crop condition at maturity were used as indicators.  Prior to all fertilizer applications, preplant soil analysis for N and P was determined.  With the exception of nutrient management, experimental crops (Iceberg lettuce, leaf spinach and broccoli) were grown according to typical grower production practices with respect to irrigation and pest management in Yuma, AZ.  In general, the granular manure performed equal to conventional fertility management programs in spinach, a crop which has a short growth period.  However, in crops which required longer periods of time to mature and where fresh cut quality is a premium (i.e. lettuce and broccoli), the level of nutrients derived from the organic product appeared insufficient to finish the crop when compared to conventional grower practices.  As a result, additional studies during the 2010 season will include studies involving midseason applications of the organic product to long duration crops.  If organic fertility shortfalls can be addressed in long duration crops, there seems to be significant potential for the granular manure product in the fresh cut organic produce industry.  Results of this 2-year study will be discussed.