| Field experiments were conducted from 2011 through 2017 to (1) evaluate the responses of vegetable crops to Crystal Green (CG) in comparison to conventional phosphorus (P) fertilizers and (2) to investigate alternative nitrogen management strategies for desert spinach production. The earlier experiments spanned from 2011 to 2016 and employed a novel P source (struvite), a granule-like based P fertilizer marketed as "Crystal GreenRTM". Responses of Iceberg lettuce (Lactuca sativa), carrot ( Daucus carota sativus), onions (Allium cepa) and potato (Solanum tuberosum) to struvite (CG), triple super phosphate (TSP), and monoammonium phosphate (MAP) were compared. Our results revealed that CG compared favorably to TSP but not to MAP when applied as a sole P source. However, certain blends or co-granulated formulations of MAP and CG often provided superior yields than MAP alone. The later studies comprised of four experiments performed from 2016 to 2017. These studies employed various nitrogen (N) sources. The N sources included enhanced efficiency N fertilizers and conventional N products applied at 0,150, and 300 kg N/ha in 2015 and 0, 100, and 200 kg N/ha in 2016. We observed that spinach yields were often maximized at N rates less than 200 kg N/ha considerably below standard commercial practices. The data also revealed that the N source fused safe nitrate (FUSN), a product developed as a substitute for dry ammonium nitrate, generally produced favorable spinach responses relative to the other dry N sources such as ammonium sulfate (AS) and urea. The controlled release fertilizer (CRF) products were observed to be effective N sources for spinach production and are viable options for enhanced efficiency. Contrarily, the nitrification inhibitors caused ammonium damage and yield depression. Overall, the experiments proved that environmentally friendly N and P fertilizers are effective nutrient sources for vegetable production on desert soils. |
