The effect of boron (B) on peanut and soybean was examined in two omission and one B fertilizer rate trial on a Typic Tropaqualf in Northern Thailand. The B rate trial was combined with a comparison of the response of sunflower, green gram, black gram, wheat, and rice in addition to peanut and soybean grown in irrigated rice-based cropping sequences over two years.Omitting B induced the hollow heart symptom in 10% of peanut kernels with the incidence of hollow hearts closely related to B concentration in the kernels. Omission of B had no effect on the appearance of soybean seed or on the grain yield of either soybean or peanut.In the B rate experiment, omitting B depressed grain yield by 50% in sunflower and by 40% to 80% in black gram, induced B deficiency symptoms in green gram and the hollow heart symptom in peanut kernels, but had not significant effect on the grain yield of soybean, peanuts, rice, or wheat. B deficiency apparently depressed grain yield in black and green gram by delaying or inhibiting reproductive development thus reducing pod set.