Manure should be mixed with earth, for it lasts only two or three years by itself, but with earth it will last twice as long; for when the manure and the earth are harrowed together the earth shall keep the manure so that it cannot waste by descending in the soil, which it is apt to do. 'Feed your working oxen before some one, and with chaff. Why? I will tell you. Because it often happens that the oxherd steals the provender.' The oxen were also to be bathed, and curried when dry with a wisp of straw, which would cause them to lick themselves. 'Change your seed every year at Michaelmas; for seed grown on other ground will bring more profit than that which is grown on your own.' Apparently the only drainage then practised was that of furrow and open ditch; and we find him saying that to free your lands from too much water, let the marshy ground be well ridged, and the water made to run, and so the ground may be freed from water. Here is his estimate of the cost of wheat growing[83]: 'You know surely that an acre sown with wheat takes three ploughings, except lands which are sown yearly; and that each ploughing is worth 6d. and the harrowing 1d., and on the acre it is necessary to sow at least two bushels. Now two bushels at Michaelmas are worth at least 12d., and weeding 1/2d., and reaping 5d., and carrying in August 1d., and the straw will pay for the threshing.'[83] The return was wretched: 'at three times your sowing you ought to have 6 bushels, worth 3s.' The total cost is thus 3s. 1-1/2d.; and without debiting anything for rent and manure, the loss would be 1-1/2d. an acre. The anonymous _Treatise on Husbandry_ of about the same date says, however, that 'wheat ought to yield to the fifth grain, oats to the fourth, barley to the eighth, beans and peas to the sixth.'[84] In the years 1243-8 the average yield of wheat at Combe, Oxfordshire, was 5 bushels per acre, of barley a little over 5, oats 7. In the Manor of Forncett, in various years from 1290 to 1306, wheat yielded about 10 bushels, oats from 12 to 16, barley 16, and peas from 4 to 12 bushels per acre.[85]