Nitrogen Rate and Timing Effects on Collard Yield and Plant Nitrogen Concentration

Abstract

As the health benefits of diets high in leafy green vegetables become apparent, there is renewed interest in the production of crops such as collards (Brassica oleracea L. Acephala Group). Although yield increases from adding N fertilizer to collards have been demonstrated, the effect of split applications of N are not well known. Therefore, the objective of this research was to examine the effect of N rate and timing on yield and N content of fall and spring collard crops. Open pollinated (‘Vates’) and hybrid (‘Flash’) collards were transplanted into 6-in. raised bare planting beds in fall and spring of a 2 yr study. Treatments consisted of ammonium nitrate (34-0-0) applied at rates of 60, 120, 180, and 240 lb N/acre either as 100% preplant or in split applications. Split applications were applied either half at transplanting and half 4 wk after transplanting, or one-third at transplanting, one-third 2 wk after transplanting, and one-third 4 wk after transplanting. Yields were increased when N was applied as a split application, and applying N in a three-or two-way split increased yields compared with those obtained when all the N was preplant. There was no further yield advantage gained when N was split into three vs. two applications. Collard yield increased with increasing rates of N. Yields were lower in fall than spring, and the hybrid Flash usually had a higher yield than open pollinated Vates in two of four crops. Collard yield response to added N was measured at N rates above the current recommended rate of 120 lb N/acre. Research Question Although they may not be a producer's principal vegetable crop, collards often are a valuable rotation or double crop. Efficient application of N to produce maximum economic yield is desirable. The objective of this work was to examine the effect of N rate and timing on yield and N concentration of open-pollinated and hybrid collards. Literature Summary Although the benefits of N fertilization for vegetable crop production have long been known, the effect of split applications of N on collard yield has not been examined fully. Additionally, cole (broccoli, cabbage, turnip greens, collards) crop yield responses to N were often found to increase with increasing rates of N, and maximum yields were often observed at the highest rates of applied N. When extremely high rates of N (>300 lb N/acre) were applied, a lack of yield response and inefficient use of N was discovered. Study Description The experiment was initiated in the fall of 1993 in northern Alabama on a Hartsell fine sandy loam. The experiment consisted of four replicates of an unfertilized check plus 12 N treatments. Nitrogen treatments consisted of four N rates: 60, 120, 180, or 240 lb N/acre, applied as 100% preplant or in split applications. Split applications were applied either half preplant and half 4 wk after transplanting, or one-third preplant, one-third 2 wk after transplanting, and one-third 4 wk after transplanting. Collards were planted in the fall and spring for 2 yr, resulting in four harvests. Collected data included fresh weight, whole plant total N concentration, and plant population at harvest. Applied Questions Did split applications of N fertilizer increase collard yield? Split applications of N fertilizer increased collard yield over yields obtained when all the N fertilizer was applied preplant. Splitting N fertilizer application into three- and two-way applications both increased collard yield over 100% preplant treatments. There was no further yield advantage when N was split into three vs. two applications. At what N rate was collard yield maximized? Collard yields were maximized at rates between 222 lb N/acre and 250 lb N/acre. These values are much larger than currently recommended (120 lb N/acre), but are similar to those found in other cole crop fertility research. Maximum profit was also obtained near these same rates of N application.