Bernadine C. Strik
Professor, Dept. Horticulture & Berry Crops Research Leader, NWREC
The objective of this research planting is to determine the long-term impact of pre-plant incorporation of sawdust and surface sawdust mulch and nitrogen fertilizer rate on yield, fruit size, fruit firmness and soil properties in Elliott blueberry.
In fall 2003, we established a new Elliott planting at the NWREC in a Willamette silt loam soil type. Planting occurred in October 2003 on raised beds that were either constructed with the incorporation of fir sawdust amendment, or left un-incorporated. Plots were then mulched with sawdust or left bare after planting. Nitrogen fertilizer was applied at three rates in the growing season of 2004 and 2005 (20, 60, and 100 lb N/acre). Fertilizer rates have been increased proportionately as the planting has aged (2006-2007: 28, 85, and 137 lb N/acre; 2008-2009: 35, 100, and 165 lb N/acre; 2010-11: 50, 150, and 240 lb N/acre). Surface sawdust mulch has been maintained as required.
There has been no significant effect of N rate on machine-harvested yield which increased from 4.8 t/acre in 2006 to 9.4 t/acre in 2011. While cumulative yield (2006-2011) has not been affected by incorporation of sawdust or mulch, plots in which sawdust was incorporated before planting had a higher cumulative yield if no mulch was used (46.1 tons/a for bare vs. 41.7 tons/a for mulched) whereas the opposite was true for plots in which no sawdust was incorporated (40.6 vs. 42.2 tons/a, for bare soil or with sawdust mulch, respectively). While leaf N concentration has been lower than recommended standards in some years, this has had no negative impact on yield. Nitrogen fertilization with the high rate decreased average berry weight in all years. Plots in which no sawdust was incorporated before planting had greater berry weight when sawdust mulch was used (2.13 g) than when plots were bare soil (2.09 g). To date, there has been no treatment effect on the firmness of berries picked by hand, just prior to machine harvest. Plants fertilized with the low rate of N had a lower fruit N concentration at harvest in 2010, but not in 2011. Fertilization rate and use of sawdust before or after planting has affected soil organic matter and nutrient content. Soil pH of plots fertilized with the high rate of N was lower than in plots fertilized with the medium or low rate of N in 2010.
In 2010-11, there was no effect of incorporation or mulch on nutrient removal in fruit. However, in 2010, Ca, B, Fe, and Cu removal in fruit were greater with the low level of N fertilization. About 15 lb N/acre, 1 lb P/acre, and 8 lb K/acre was removed in fruit harvested in 2010 and 2011.
There was no effect of N fertilization rate on the dry weight of prunings removed in January 2011. Pruning removed an average of 14 lb N/acre, 1.5 lb P/acre, 7 lb K/acre, and 3 lb Ca/acre.
We will collect one more year of data in 2012 and get a second year’s data on the amount of carbon sequestered in a mature blueberry field (data not shown here).
Thank you to the following individuals for their significant contributions to this project: Gil Buller (Senior Research Assist., NWREC); Linda White (former M.S. graduate student, now OSU faculty, Dept. Hort.); John Lambrinos (Dept. Hort.); Denise Nemeth (Ph.D. student, Dept. Hort.); David Bryla (USDA-ARS); John Hart (Dept. Crop and Soil Sci.); Wei Yang (NWREC).
We greatly appreciate the financial, research grant support and in-kind contributions from: Oregon Blueberry Commission; Agricultural Research Foundation; Littau Harvesters Inc.; Fall Creek Farm & Nursery