Boron Uptake by Canola and Distribution in some Saskatchewan Soils
Boron (B) is an essential element for plants. Deficiency of this element hinders plant growth and development in many parts of the world. Little is known about B chemistry and availability in Saskatchewan soils. Growth chamber and field experiments were conducted using a series of Saskatchewan soils to determine the effect of different rates of added B to canola (Brassica napus L. cv Sprint) on yield and plant B concentrations. Four different extracting techniques to determine readily available B in the soil were also compared, followed by a four step sequential B fractionation procedure to reveal the nature of soil B in nine selected soils with different textures and management histories. A growth chamber experiment was conducted using two different soils, the Porcupine Plain and Carrot River Associations, representing Gray Luvisols that were suspected of B deficiency in the field. Boron was applied at amounts of 1, 2, and 3 mg kg-1 soil. Seed yield of canola increased about 13% and 12% (not significant) over the control in the Porcupine Plain and the Carrot River soils, respectively, as a result of B fertilization, with the highest yield at the 3 mg kg-1 rate. In the field experiment, no significant yield response to B fertilization was observed. In growth chamber experiment the whole plant B concentration was significantly increased with increasing rates of B application in the Carrot River soil. For the sequential B extraction study, nine composite soil samples were collected from the Brown and Gray Luvisol Great Group. One composite soil sample was used from Pakistan to provide a contrast. Four different techniques: 1) hot water (HW), 2) 0.01M CaCl2, 3) 1M NH4-acetate, and 4) anion exchange membranes (AEM) were used to extract the readily soluble B fraction from the selected soils. The other four fractions, specifically adsorbed, oxide bound, organically bound, and residual B were determined sequentially on the same soil sample. On average, hot water extracted more B than that extracted by 0.01M CaCl2, 1 M NH4.acetate, and AEM B. In almost every soil, readily soluble B represented only a small proportion of the total B concentration, irrespective of the extraction method used to determine the readily soluble B pool. The major portion of soil B existed in the residual or occluded form, which accounted for about 97% of the total soil B. The mean concentration of organically bound B was higher than that of mean content of oxide bound and specifically adsorbed B in all the soils studied, irrespective of the readily soluble B extracting solution used. Among the soil characteristics, cation exchange capacity (CEC) appeared to be an important characteristic controlling the B pools. No significant correlation was found between organic carbon and the B pools, except hot water soluble (HWS) B, which was positively correlated to organic carbon content. Correlation coefficients between the B pools and particle size distribution were poor. Dithionite extractable Fe-oxy-hydroxides were also not correlated with B fractions. Correlation between carbonates and B pools were found to be statistically insignificant. Boron application appears to increase seed yield in canola, but this increase was not statistically significant, suggesting further research in this area. Among the soil characteristics, CEC emerged to be an important characteristics controlling the B availability and pools in the soils studied.