41. Where, for any assessment year, the net result of the computation of income under the head “Agricultural income” is a loss to the assessee, and such loss has not been wholly set off under section 37, so much of the loss as has not been so set off, or the whole of the loss, where the assessee has no income under any other head or has income only under the head “Capital gains”, shall be carried forward to the next following assessment year, and- (a) it shall be set off against agricultural income, if any, of the assessee assessable for that assessment year; and (b) if the loss cannot be wholly so set off the amount not so set off shall be carried forward to the next assessment year and so on for not more than six successive assessment years.