Calculating the cost of a year without land-tilling
The approach appears to be static. An intertemporal approach would recognize that part of the period's forgone production would have been used for investment, augmenting the capital base. So we also lose future consumption. But let's skip that.

In order to categorize what the country will lose (and who is going to lose it) I decompose output into certain categories and comment on each one

Output =
+ Imported materials  (we don't care what happens to them)
+ Services offered from abroad  (we don't care what happens to them)
+ Locally produced materials in other sectors  (will there be demand for their products from other sectors of the economy? Will they be able to export them? -possibly lost income here)
+ Services offered by locals (How much of them will be used to manage the compensating imports? -possibly lost income here)
+ Rents of land owners who do not engage in farming (lost income)
+ Wages of people working the land, i.e. "Direct Labor" (lost income)
+ Wages of other personnel in the sector (will they be needed to manage imports? -possibly lost income here)
+ Depreciation (equipment will erode by the simple passage of time, but land may even appreciate in terms of productivity-after all the biblical commandment has clear practical motives. So on the balance?)
+ Profits of farmers/entrepreneurs (lost income)

A basic conclusion from the above, is that by stopping production in one sector, we may also lose some production in other sectors.

...and think also about taxes.