Long term capital gain tax on agricultural land

Sir,

I would like to know that if  Karta of (HUF) purchased a Agricultural Land in June-2007 for Rs. 17 Lac & Sale the Land in Apr-2012 for Rs. 40 Lac. The Land is situated at 6 KM from city limit. He has also 7/12 as agricultural income. If Karta invest the profit amount i.e. 23 Lac to purchase other agricultural land. The amount of profit taxable or  he will get exemption under section 54 B?