Long-term field experiment on the application of slow-release boron fertilizer Part 1 Effect of boron on crop growth

Abstract

A slow-release boron (B) fertilizer was applied annually for 15 years to investigate the effect of B on the growth of crops in three soils: a diluvial soil, volcanic ash soil and granitic soil. Cumulative B applications were 20.4, 17.9 and 31.4 kg ha^-1, respectively. The relative yield in B treated plots (called FTE plots) was always higher than that in those without the applied B (called original plots). Symptoms of deficiencies in B appeared in original plots after 2–4 years cultivation of crops, and worsened year after year. On the other hand, toxicity symptoms due to excess of B never appeared in any crops in FTE plots; rather, those crops showed healthy growth throughout the 15 years. Similarly the B concentration in crops in FTE plots always remained in the adequate range. The content of hot water soluble B in the soil of original plots, where serious deficiency symptoms appeared in crops, were generally less than 0.3 mg kg^-1. The hot water soluble B contents in the soil of FTE plots increased to about 1.0 mg kg^-1 in the 15th year. Although the granitic soil received the largest B application, hot water soluble B in this soil increased to a lesser extent than in the other soils. The total amount of B taken up by crops was about 10% of the amount of B applied, suggesting that either significant residual B remained in the soil, or significant leaching occurred. These issues are the subject of the following paper.