Influence of Organic Versus Synthetic Nitrogen Fertigation on Sweet Corn Yield, Quality, and Nutritional Quality

Consumer awareness and demand for fresh, high quality and nutritious organic sweet corn (Zea mays L. convar. saccharata var. rugosa) has led to great consumer demand from organically certified farms. Our objectives were to determine yield, quality, and nutritional content of sweet corn fertigated with organically derived nitrogen (N) versus synthetically derived N under conventional cultural practices to examine the effects of the N source exclusively.  A four factor completely randomized block design experiment including planting date, cultivar, fertilizer source and rate was conducted under two separate soil conditions at Clemson Coastal Research and Education Center, Charleston SC.  Two sweet corn shQ cultivars 3175 and 378a were grown with synthetic and organic N sources at 84, 168, and 336 kg·ha^-1 N, respectively, at two empirically chosen planting dates.  Data collected included cobs/ha and kg·ha^-1, quality, nutritional content including mineral, phenolic acid and carotenoid contents were determined.  Of the two planting dates, it was determined that the 23 Mar. 2009 planting date was superior in yield to the 20 Apr. 2009 planting date.  Synthetic N at the 4x rate produced greater yields on depleted soils when compared to organic N at the 4x rate on enhanced soils.  On enhanced soils, synthetic N at the 1x rate nearly equaled the 4x organic N rate.  The lowest yielding were control plots without N on depleted soils, followed by the organic N source at the 1x rate on depleted soils.  The greatest yielding plots were synthetic N source at 4x rates on depleted soils followed by organic N at 4x rates on the enhanced soils.  Phenolic acid content mg·g^-1 did not differ for either cultivar on depleted soils; however, cultivar 378a contained 11% more phenolic acid mg·g^-1 on enhanced soils when compared to depleted soils.  The contrary was observed for carotenoids for lutein, zeaxanthin, and β-cryptoxanthanin, which was 21%, 31%, and 12% µg·g^-1 greater in depleted soils compared to enhanced soils, respectively.  Lutein increased with fertilizer rate with the 336 kg·ha^-1 N rate producing the greatest lutein content of 0.99 µg·g^-1.  There was no conclusive evidence that organic N fertilized sweet corn was superior to synthetic N fertilized sweet corn with regard to yield, quality, and mineral, phenolic acid, and carotenoid contents.