Alex, that's quite tricky. In acid soils with low pH , calcium usually remains low due heavy leaching .It is very difficult to get a soil environment having low pH with high calcium to predispose for boron deficiency...

The answer I believe is very in a low pH soil with high Calcium we can improve the boron status.

For instance the boron can be applied as a drip application or as foliar and seed application for instance.

Also the use of humic materials can be useful in improving boron use of efficiency.

The nature of soluble humics is they are high in both anionic and cationic exchange capacity.

An organic matter which is an boron source is vermi castings which provide also soluble humic material.

A very good way to deal with tropical acid soils is understanding they are compromised many times by Silicon deficiency multiple macro and micro elements and can have toxicity issues.

The addressing of this issue would need to accompany the use of borates humates and is demonstrated to strengthen plant adaptive mechanisms.

It would be good to shed light on the issues by doing background complete soil and plant analysis and then experiment with balancing strategies to be tested out.

Boron can be both toxic and deficient concern on the toxicity has led to much undiagnosed and untreated boron deficiencies. Members of the crucifer family are good deficiency bio indicators and the presence of hollow heart can denote a condition of need of attention. The recommended soil analysis should be complemented with plant foliar analysis which can be use to help diagnosis a condtion and confirm remedies are indeed working.

If you have some analyses I would gladly review and give some ideas of approaching and testing confirmation routes.

using foliar application or foliar spraying of boron,or application of nano-boron fertilizer .