wheat

args={...}
delay=tonumber(args[1] or 1200)

function ensureFuel()
    while turtle.getFuelLevel()==0 do
        shell.run'refuel all'
        sleep(10)
    end
end

function go(action)
    ensureFuel()
    i=0
    while action() do
        i=i+1
        turtle.select(1)
        turtle.digDown()
        turtle.select(16)
        turtle.placeDown()
        sleep(1)
    end
    return i
end

local i
while true do
    i=go(turtle.forward)
    turtle.select(1)
    turtle.drop()
    turtle.select(16)
    turtle.drop(math.min(turtle.getItemCount(16)-i,0))
    sleep(delay)
    i=go(turtle.back)
end