Oak farm by Num

function moveDown()
    while(not turtle.down()) do turtle.attackDown() end
end

function moveUp()
    while(not turtle.up()) do turtle.attackUp() end
end

function moveForward()
    while(not turtle.forward()) do turtle.attack() end
end

function moveBack()
    while(not turtle.back()) do sleep(1) end
end

function prepPlant()
    turtle.select(1)
    moveForward()
    turtle.suckDown()
    moveForward()
    turtle.suckDown()
    moveBack()
    moveBack()
    if(turtle.getItemCount(1) < 64) then error("Not enough saplings.") end
    if(turtle.getItemCount(2) < 64) then error("Not enough bonemeal.") end
end

function plant()
    moveBack()
    turtle.select(1)
    turtle.place()
    turtle.select(2)
    turtle.place()
end

function plant7()
    for i = 1,7 do
        plant()
    end
end

function plant8x8()
    for i = 1,4 do
        plant7()
        turtle.turnRight()
        plant()
        turtle.turnRight()
        plant7()
        turtle.turnLeft()
        plant()
        turtle.turnLeft()
    end
end

function harvest()
    turtle.dig()
    moveForward()
    turtle.digUp()
    turtle.digDown()
    turtle.suckDown()
end

function harvest7()
    for i = 1,7 do
        harvest()
    end
end

function harvest8x8()
    for i = 1,4 do
        harvest()
        turtle.turnRight()
        harvest7()
        turtle.turnLeft()
        harvest()
        turtle.turnLeft()
        harvest7()
        turtle.turnRight()
    end
end

function prepHarvest()
    turtle.select(1)
    turtle.digUp()
    moveUp()
    turtle.turnRight()
end

function to2ndLayer()
    turtle.turnLeft()
    turtle.dig()
    moveForward()
    for i = 1,3 do
        turtle.digUp()
        moveUp()
    end
    turtle.turnRight()
    turtle.turnRight()
end

function dropWood()
    for i = 1,16 do
        turtle.select(i)
        turtle.dropDown()
    end
end

function toStartPoint()
    turtle.turnLeft()
    turtle.dig()
    moveForward()
    for i = 1,4 do
        turtle.digDown()
        moveDown()
    end
    turtle.turnLeft()
    for i = 1,7 do
        moveForward()
    end
    dropWood()
    turtle.turnLeft()
    moveForward()
    turtle.turnRight()
end

while(turtle.getFuelLevel() > 500) do
    prepPlant()
    plant8x8()
    prepHarvest()
    harvest8x8()
    to2ndLayer()
    harvest8x8()
    toStartPoint()
end
print("Terminated: Low fuel level.")