Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2010
Publication Date: 6/1/2010
Publication URL: http://www.ars.usda.gov/Services/docs.htm?docid=10135
Citation: Smith, T.E., Grattan, S.R., Grieve, C.M., Poss, J.A., Suarez, D.L. 2010. Salinity's influence on boron toxicity in broccoli: I. Impacts on yield, biomass distribution, and water use. Agricultural Water Management. 97(6):777-782. Interpretive Summary: Boron (B) is essential for crops, but the element has a narrow concentration window between that which is nutritionally adequate that which causes B toxicity symptoms, plant injury and subsequent yield reductions. Excess B often are associated with saline soils and waters in many regions of the world including Chile, Saskatchewan Province in Canada, India, Australia, and western Fresno County, California. It is important, therefore, to evaluate B uptake by plants under saline conditions inasmuch as B toxicity may be confounded with the associated problems of salt accumulation. This study was conducted in greenhouse sand cultures with broccoli as the test crop. Broccoli is rated as moderately tolerant to salinity, but moderately sensitive to boron in the rootzone. Plant response to two irrigation waters was compared: (1) chloride-dominated salinity and (2) saline-sodic waters typical of drainage waters present in the San Joaquin Valley of California. Treatments were three irrigation water salinity levels (2, 11, 18 dS/m) and three boron concentrations (0.5, 12, 24 mg/L). Regardless of the type of the irrigation waters applied, increases in both salinity and boron concentration reduced shoot growth and broccoli head yield. Broccoli, however, was more tolerant to boron when the plants were salt-stressed. The combined effects of salinity and excess boron appears to be antagonistic, that is, the outcome of the two factors, applied together, is less than the sum of the effects of either boron or salinity applied separately.
Technical Abstract: Research addressing the interactive effects of the dual plant stress factors, excess boron and salinity, on crop productivity has expanded considerably over the past few years. The purpose of this research was to determine and quantify the interactive effects of salinity, saltcomposition and boron (B) on broccoli (Brassica oleracea L.) biomass distribution and consumptive water use. A greenhouse experiment was conducted using a sand tank system in which salinity-B treatment solutions were supplemented with a complete nutrient solution. Chloride-dominated salinity and salinity characteristic of California's San Joaquin valley (SJV), or sulfate-dominated, were tested at ECw levels of 2, 11 and 18 dS m-1. Each salinity treatment consisted of boron treatments of 0.5, 12 and 24 mg L-1. Plant head yield and shoot biomass were significantly reduced by both salinity and boron. Moreover, there was a significant salinity-boron interaction where increased boron was relatively less detrimental under saline conditions. These results occurred regardless of the salt solution composition (chloride or SJV). We found that an 'interactive model' better described our growth response than did a 'single stressor yield model'. Salinity and boron also affected the distribution of shoot biomass. Regardless of salt type, as salinity increased, the fraction of biomass as leaf tissue increased while the biomass fraction as stems and particularly heads, decreased. However, an increase in B at low or high salinity with the SJV composition, decreased the head biomass fraction. This was not observed at moderate salinity, nor on any plants treated with Cl-dominated salinity. Cumulative evapotranspiration (ET) was also reduced by increased salinity but water use efficiency (WUE) was not. WUE was reduced by increased boron, but only at the low and high salinity levels. Using an isotopic method to separate evaporation and transpiration, we found the vast majority of the water lost from the tank system was by transpiration (> 90%) regardless of treatment.