Sale of Converted Agricultural Land to Non- Agricultural Land - Long Term or Short Term Capital Gain

One of my relatives have recently converted their Agricultural Land to Non Agricultural Land (Originally purchased in 1950's) and immediately after conversion sold the land for a consideration of approximately Rs 50 Lakhs. 

Will this conversion and immediate sale of land be considered as sale of Long Term Capital Asset or Short Term Capital Asset? What will be the period of holding for Capital Gain Taxation? (Re-investment of the sale consideration will be done within next few weeks for claiming exemption.)

Require clarity on this

Thanks in advance :)