Evaluation of an Organic Nitrogen Source in a Yellow Squash - Collard Rotation

Abstract

In-season nitrogen (N) management is a common challenge in organic vegetable production. Especially when using polyethylene mulch combined with fertigation. There is a need for a highly soluble quick release N source that is suitable for fertigation in organic vegetable production. Hydrolyzed fish fertilizer (HFF) has been used as a supplemental fertilizer in organic production for many years. Yield with organic N supplied by HFF was compared to that of inorganic N. A crop rotation of yellow squash (Cucurbita pepo) and collards (Brassica oleracea var. acephala) was used. Three N sources were used in the experiment; HFF, Inorganic N source with secondary and micronutrients (INORGWM), and Inorganic N without secondary or micronutrients (INORGWO). The three N sources were applied at 100%, 80%, and 60% of the recommended N rates for each crop. To evaluate the HFF as an N source it was necessary to equalize other nutrients across all treatments. The experiment was arranged as a randomized complete block design consisting of 10 treatments with 4 replicates. White on black polyethylene mulch was installed along with drip tape. The yellow squash was seeded on 7/6/12 and was harvested 3 times weekly from 8/6 – 8/27. Yellow squash had a 30% higher yield with the inorganic N source treatments compared to the HFF. The collard crop was transplanted on 10/2/12 and harvested 12/12/12. Collards had 21 % higher yield with INORGWM compared to the HFF. However, all collard treatments with secondary and micronutrients yielded significantly higher than the treatments with the micronutrients withheld. The second collard crop was planted on 3/22/13 and harvested on 5/17/13. Yield was significantly reduced across all N treatments. The highest yields were produced in the INORGWM treatments followed by those grown in the HFF treatments. Overall yield was reduced by 50% from those in the 2012 crop. The final summer squash crop also had greatly reduced yields. The squash grown in the inorganic N treatments produced the highest yields. Those grown in the HFF yielded 16% lower than the two inorganic N sources. Overall yield was reduced by 60% from the yield produced in the 2012 crop. Though yields were reduced in the HFF treatments, the premium price associated with organic products was enough to offset the reduced yield. Upon completion of the rotation, a detailed economic analysis was conducted and determined that over the course of the rotation, the HFF treatments were the most profitable. Total profit from the HFF treatment was 230% greater than the INORGWM treatment and 328% higher than the INORGWO. If growers can obtain the price premiums associated with organic produce, the use of HFF can be an economically feasible option in organic vegetable production.