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Abstract
Nitrogen and water management are essential factors for achieving adequate crop growth and development in organic production systems. A three-year field study examined effects of different forms of organic N fertilizers applied at side-dress and with different irrigation application rates on leaf, stem, and floret yields, volumetric soil water content (P v), and crop water use efficiency (WUE) in organically-grown broccoli (Brassica oleracea L.) in two regions of California; Santa Cruz (UCSC farm) and Five Points (Harris farm). At preplant, ‘compost only’ treatment (CO) was applied at 140 kg·ha−1 of N with an additional 112 kg·ha−1 of N applied as side-dress in one of the following forms: (1) fish powder (FP); (2) Phytamin [bloodmeal and feathermeal mix (BF)]; (3) BF mixed with NaNO3 (SN), or (4) seabird guano (SG). Leaf, stem, and floret yields collected from the UCSC farm had a greater response to additional N from side-dressing treatments irrespective of the form than plants at the Harris farm in all years. The interaction of side-dress and irrigation treatment significantly influenced leaf, floret, and stem yields at both locations. A greater Pv was measured from the 0–15, 15–45, and 45–90 cm depths when treated at 150, 100, and 80% crop evapo-transpiration (ETc), respectively, on both farms. Soil samples collected from the 45–90 cm depth had the highest Pv levels at both locations. The Harris farm had higher levels of Pv than the UCSC farm at all depths. The greater WUE was achieved with 80 and 100% ETc at the UCSC farm and with 100% ETc at the Harris farm. Based on the results, it appears that a side-dress application of 112 kg·ha−1 of N in addition to 140 kg·ha−1 of N applied as compost at preplant, and irrigation at either 80 or 100% ETc on the UCSC farm, and at 100% ETc on the Harris farm achieves the highest level of WUE. Organic broccoli growers need to consider fertility status of the site, soil type, seasonal precipitation, and form of side-dress for achieving highest yields in a sustained manner.