Graduate Thesis Or Dissertation
 

Effects of boron rates and differential irrigation on bush green beans and cauliflower

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  • Five boron rates and seven water levels were applied to bush green beans (Phaseolus vulqaris cv Oregon 91G) and to cauliflower (Brassica olereacea var. botrytis, cultivar "Snowball Y") in 1989 and 1990 to evaluate their effects on total yield of both crops and on outer quality, head hollowness and internal discoloration of cauliflower curds. Of the five B rates (0,1,3,6 and 9kg/ha) three (0, 3 and 9 kg/ha) were monitored to evaluate B concentrations at soil depths of 0-15, 15-30, 30-45 and 45-60 cm. In each season, B concentrations were analyzed at a high (wet) level of applied water. An overall evaluation comparing the starting and ending levels of B after two years was conducted at two levels of applied water (high and low). Soil applied B rates of 9 kg/ha significantly reduced bean yields in 1989 and 1990. Boron concentrations in the trifoliate leaf tissue at the highest (wet) water level in 1989 and 1990 ranged between 22 to 72 mg/kg for the five B rates. Tissue concentrations at the lowest (dry) Water level in 1990 ranged from 23 to 32 mg/kg B. Soil B levels for both years had an overall range of 0.22 to 1.81 mg/kg. Injury to beans occurred at soil concentrations equal to or greater than 1.0 mg/kg B. An added experiment (0,9,18 and 36 kgB/ha) in 1990 produced highly significant reductions in bean yields at B rates of 18 and 3 6 kg/ha. Yields did not vary significantly, however, between 0 and 9 kgB/ha. Boron concentrations in whole plant samples at the first trifoliate leaf stage ranged from 4 3 to 3 52 mg/kg. Soil B levels ranged from 0.3 5 to 4.07 mg/kg. Applied water levels of 77% and 69 to 87% of a calculated reference evapotranspiration coefficient (ETo) produced highest yields of bean pods in 1989 and 1990 respectively. Optimum yields for both seasons occurred when soil moisture levels (% moisture/ volume) were depleted to no less than 50% of available soil moisture. Total yields, inner quality and outer quality of cauliflower were not significantly affected by soil applied B rates as high as 9 kg/ha (as compared to 0, 1, 3 and 6 kgB/ha) during both the 1989 and 1990 seasons. Boron concentrations in leaf tissue at the highest (wet) water level ranged from 13.2 to 23.8 and 34.8 to 70.9 mg/kg in 1989 and 1990 respectively. Boron concentrations in leaf tissue were higher at the highest water level than at the lowest water level. Post harvest soil B concentrations ranged from 0.31 to 0.82 mg/kg at the highest water level in 1989 and 1990 respectively. In general, soil B concentrations were higher at the lowest (dry) water levels than at the highest water level. Highest yields were achieved at applied amounts of water that equaled 104 and 80% of ETo in 1989 and 1990 respectively. Corresponding soil moisture data (% moisture/volume) showed optimum yields occurring when available moisture remained above 50%. The frequency of good outer quality curds increased as water amounts increased. The frequency of good inner quality curds decreased as water amounts increased. Marketable yields at the lower moisture regimes, however, were marginal. Internal quality appeared to be a function of harvest date in this experiment. The frequency of head-hollowness and internal discoloration both decreased as the harvest season progressed. Percent good inner quality ranged from 48.5 to 84.7 and 34.9 to 91.1 between first and last harvests in 1989 and 1990 respectively. Boron migration or loss through the soil profile was greatest out of the top 0-15 cm depth and at the 9 kgB/ha rate. Losses as high as 39 and 49% in 1989/1990 and 1990/1991 seasons respectively, were found as a result of differential dates of soil sampling. In an additional experiment in the mid-summer of 1990 where rates of 9, 16 and 32 kgB/ha were applied, losses of B from the 0-15 cm depth ranged from 35 to 49%.
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