"The spring ploughing should be followed up with frequent stirring of the soil until it is reduced to dust, so that there may be no necessity, or very little, of harrowing after the land is seeded: for the ancient Romans said that a field was badly ploughed which had to be harrowed after the seed had been sown. "A farmer should himself make sure that his ploughing has been well done, not alone by inspection, for the eye is often amused by a smooth surface which in fact conceals clods, but also by experiment, which is less likely to be deceived, as by driving a stout stick through the furrows: if it penetrates the soil readily and without obstruction, it will be evident that all the land there about is in good order: but if some part harder than the rest resists the pressure, it will be clear that the ploughing has been badly done. When the ploughmen see this done from time to time they are not guilty of clod hopping. "Hence wet land should be broken up after the Ides of April, and, when it has been ploughed at that season, it should be worked again, after an interval of twenty days, about the time of the solstice, which is the eighth or ninth day before the Kalends of July, and again the third time about the Kalends of September, for it is not the practice of experienced farmers to till the land in the interval after the summer solstice, unless the ground shall have been soaked with a heavy down-pour of sudden rain, like those of winter, as does some times happen at this season. In that event there is no reason why the fallow should not be cultivated during the month of July. But when you do till at this season beware lest the land be worked while it is muddy: or when, having been sprinkled by a shower, it is in the condition which the country people call _varia_ and _cariosa_, that is to say, when, after a long drought, a light rain has moistened the surface of the upturned sod but has not soaked to the bottom of the furrow. "Those plough lands which are cultivated when they are miry are rendered useless for an entire year--they can be neither seeded nor harrowed nor hoed--but those which are worked when they are in the state which has been described as varia, remain sterile for three years on end. We should, therefore, follow a medium course and plough when the land neither lacks moisture nor yet is deep in marsh."] [Footnote 31: Columella (II, 13) justly says about manure, "Wherefore if it is, as it would seem to be, the thing of the greatest value to the farmer, I consider that it should be studied with the greatest care, especially since the ancient authors, while they have not altogether neglected it, have nevertheless discussed it with too little elaboration." He goes on (II, 14) to lay down rules about the compost heap which should be written in letters of gold in every farm house.