Enhancing Fertilizer Efficiency in High Input Cropping Systems in Florida

Abstract

During the last century, a number of strategies have been used to determine optimal N-fertilizer rates and to develop appropriate N-fertilizer recommendations for intensively-managed cropping systems. However, these strategies lack a system-based approach and the precision needed to warrant high yields while addressing environmental concerns in a cost-effective manner. Therefore, a more holistic approach is required to enhance fertilizer use efficiency (FUE) in high input agricultural systems that pose both large environmental and economic risks. This article presents a physiological basis for improving FUE in these systems by linking physiological crop nutrient requirements with nutrient uptake efficiencies as affected by root characteristics, crop N demand, and production management practices. Starting at the crop and field level we outline key processes affecting crop N demand and uptake efficiency. For this purpose we reviewed key scientific papers that describe yield response and fertilizer uptake efficiencies with special reference to pepper (Capsicum annuum L.), potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum L.) crops in Florida production systems. This because such systems are especially prone to N leaching. Based on this review it is evident that yield response to fertilizer for most crops tend to be inconsistent both within and across locations. Therefore, use of standard recommendations may not be appropriate since they pose substantial economic and environmental risks.

In terms of production efficiencies, at low fertilizer application rates values were 100–397, 63–243, 82–264 kg extra yield per kg fertilizer for tomato, pepper, and potato, respectively. Corresponding values at recommended fertilizer rates were reduced to 24–213, 30–152, 48–173 kg extra yield per kg fertilizer. However, using an economic yield analysis it was shown that under adverse conditions, use of higher fertilizer rates is correctly perceived by farmers as viable strategy for minimizing economic risk. In terms of uptake efficiency, even at low N-fertilizer rates the fraction of applied fertilizer that was removed by the crop was highly variable, with values being 43–71%, 16–71%, and 4–81% for tomato, pepper, and potato, respectively. Moreover, overall crop N recovery tended to decline with increasing N-application rates. Since any residual soil-N may be readily lost by soil via leaching, this implies that even at low fertilizer application rates, environmental impacts may still occur. Furthermore this environmental risk is greatly increased at higher application rates. These results thus are in contrast with those for the economic analysis, thus pointing to potential stakeholder conflicts. Integration of different data sets to elucidate more generic trends showed that changes in relative N uptake during the crop growth cycle followed distinct patterns. These patterns were relatively consistent across crops, years and locations. Thereby they may be used as a scientific base to structure tactical guidelines for more efficient in-season fertilizer management based on actual crop growth processes. This insight is especially useful for enhanced designing of fertilizer applications schemes or the engineering of controlled release fertilizer materials. Via improved synchronization of nutrient supply with crop demand both economic and environmental production goals thus may be attained. Such approach thereby may afford producers with cost-effective production options that can be readily integrated in future best management practices for high input cropping systems.