Submitted to: Journal of Vegetable Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2006
Publication Date: 8/1/2007
Citation: Pasakdee, S., Banuelos, G.S., Shennan, C., Cheng, W. 2007. Organic n Fertilizers and Irrigation Influence Organic Broccoli Production in Two Regions of California. Journal of Vegetable Science. 12:27-46. Interpretive Summary: Organic agriculture is steadily increasing in popularity and in planted acreage throughout California. Sources of organic nitrogen and water application are especially important in producing yields of economic value from high value vegetable cash crops, e.g., broccoli. Our study examined the influences of different forms of nitrogen side-dress and irrigation rates on organic broccoli production in two different regions of California, Santa Cruz (UCSC farm) and Five Points (Harris farm). Side-dress treatments consisted of: compost only (no side-dress), fish powder, phytamin, phytamin and NaNO3, and seabird guano, and irrigation rates consisted of: 80, 100, and 150% crop evapotranspiration. Yield increases were observed at UCSC farm with side-dress treatments at both 80 and 100% Etc and slight yield increases with side-dress treatments at 100% Etc were observed at Harris farm. Water treatments were difficult to maintain at Harris farm because greater than normal precipitation occurred, while less than normal rain occurred at the UCSC farm. The lack of yield response to side treatments at Harris Farm was likely due to the fact that Harris Farm had been organically farmed for more than 5 years, while the UCSC farm had been organically farmed for only 1 year. The study shows that the application of a N side-dress is essential to a newly-converted organic farm like the UCSC farm, however, a N side-dress may not be as necessary to improve yield on a farm with a long history of applying organic amendments, e.g., Harris farm. Organic broccoli growers need to consider fertility status of the farm site before applying additional N via side-dress treatments, and they need to take precipitation rates into consideration for determining water application rates.
Technical Abstract: Organic agriculture production is rapidly expanding in the US. Fertility sources and their nutrient availablility for plant uptake are difficult to predict with organic products. Hence, nitrogen and water management are essential factors to consider for achieving adequate crop growth and development in organic production systems. A 3-year field study examined effects of different forms of organic N fertilizers applied at side-dress with different irrigation application rates (80, 100, 150% Etc) on yield, volumetric soil water content (Pv) and crop water use efficiency (WUE) in organically-grown broccoli in two regions of California; Santa Cruz (UCSC farm) and Five Points (Harris farm). At preplant, compost was applied at 140 kgN/ha with an additional 112 kgN/ha applied as side-dress as either: fish powder, Phytamin, Phytamin and NaNO3, or seabird gauno. Yields from UCSC farm had a greater response to all side-dressing treatments than yield responses observed at Harris farm. Harris farm had higher levels of Pv than the UCSC farm for 0-15, 15-45, and 45-90 cm depths. Excessive precipitation at Harris farm reduced water treatments and below normal precipitation at UCSC farm contributed to the different WUE rates at both sites. The greater WUE values were achieved with 80 and 100% Etc at the UCSC farm and with 100% Etc at the Harris farm. Application of a N side-dress to a preplant application of compost is more essential to a newly-converted organic farm like the UCSC farm and should dramatically improve yields over at least three years of application, however, a N side-dress application may not be as necessary to improve yield on a farm (Harris) with a long history of applying organic amendments. Water management and WUE are also dependent upon the precipitation occurring during the growing season.