Here is an breakdown of the game turn:

1. current year is incremented
2. report how many people died
3. report how many people were born
4. if there is a plague, apply the plague results
5. report population
6. report acreage
7. report harvest
8. report destroyed bushels
9. report current bushels
10. determine if game is over, if so, end game
11. generate price for an acre, report price for an acre
12. prompt for number of acres to purchase
12a. if <0, quit
12b. if =0, goto 13
12c. if insufficient bushels, goto 12
12d. add acres, remove bushels, goto 14
13. prompt for selling acres
13a. if <0, quit
13b. if =0, goto 15
13c. if insufficient acres, goto 13
13d. remove acres, add bushels
14. prompt for bushels for eating
14a. if <0, quit
14b. if insufficient bushels, goto 14
14c. deduct bushels for eating
15. prompt for acres to plant
15a. if <0, quit
15b. if insufficient acres, goto 15
15c. if insufficient bushels, goto 15
15d. if insufficient population to do planting, goto 15
16. deduct bushels for planting
17. generate harvest results, determine new population
18. determine how many bushels are destroyed
19. add harvested bushels, remove destroyed bushels
20. determine fed population, determine deaths
21. goto 1

Each turn, the player only controls three things:
A) the conversion of bushels to acres or acres to bushels
B) the number of bushels to feed the population
C) the number of acres to plant

the player indirectly influences population growth, by controlling the number of acres and the number of bushels

the player does NOT control:
if bushels are destroyed by rats
if a plague strikes

the player can, however, minimize the impact of bushels being destroyed by spending as many of his bushels as he can on planting, feeding the population, and acreage, as the destruction takes place pre-harvest.

the player has no control whatsoever on plagues.

however, plagues are not a bad thing, from the point of view of the end game.

at game's end, there are four outcomes:

really bad: starving more than 45% of the population in 1 turn, starving an average of more than 33% of the population each turn, or ending with fewer than 7 acres per person
bad: starving an average of more than 10% of the population each turn, or ending with fewer than 9 acres per person
mediocre: starving an average of more than 3% of the population each turn, or ending with fewer than 10 acres per person
good: starving 3% of the population or fewer each turn on avera, and ending with at least 10 acres per person

according to the end game, provided you don't starve anyone, the more acres per person you have, the better.
so, to get more acres per person, you either need to buy more acres, or lose some people.
starving them is no good, because if you average more more than 3% starvation, you lose the good status.
fortunately, the plague chance is 15%, which means that over 10 turns, there is an 80% chance that at least one plague will break out.

so, the ideal strategy for this game:

feed all of your people every turn
plant as many acres as you can every turn
buy and sell acres as needed to have a minimal number of bushels at the end of the turn(minimize the effect of rats)
hope for a plague

can you always win? no. you might get the worst crop yield for a few turns in a row. but that has nothing to do with anything that is player choice, so that is just bad luck.

one thing that this game needs badly is a better scoring system.

my first thought is that we can convert the number of bushels, acres, and people into points of some kind, and that'll give a metric.

1 bushel = 1 point
1 acre = 22 points (average price of an acre)
1 person = 25 points (average crop yield per acre times the number of acres a person can work in a turn)