also took interest in what type of manure was best for the soil. The best was poultry manure, and cow manure one of the worst. Sheep and goat manure were also good. Donkey manure was best for immediate use, while horse manure wasn't good for grain crops, but according to Marcus Terentius Varro, it was very good for meadows because "it promotes a heavy growth of grass plants like grass." Economics In the grain-growing area of north Africa, centered on the ancient city of Carthage, a family of six people needed to cultivate 12 iugera/ 3 hectares of land to meet minimum food requirements (without animals). If a family owned animals to help cultivate land, then 20 iugera was needed. More land would be required to meet subsistence levels if the family farmed as sharecroppers. In Africa Proconsularis in the 2nd century CE, one-third of the total crop went to the landowner as rent (See Lex Manciana). Such figures detail only the subsistence level. It is clear that large scale surplus production was undertaken in some provinces, such as to supply the cities, especially Rome, with grain, a process known as the Cura Annonae. Egypt, northern Africa, and Sicily were the principal sources of grain to feed the population of Rome, estimated at one million people at its peak. For yields of wheat, the number varies depending on the ancient source. Varro mentions 10:1 seed-yield ratio for wheat as normal for wealthy landowners. In some areas of Etruria, yield may have been as high as 15:1. Cicero indicates In Verrem a yield of 8:1 as normal, and 10:1 in exceptionally good harvest. Paul Erdkamp mentions in his book The Grain Market in the Roman Empire, that Columella was probably biased when he mentions a much lower yield of 4:1. According to Erdkamp, Columella wanted to make the point that "grain offers little profit compared to wine. His argument induces him to exaggerate the profitability of vineyards and at the same time to diminish the yields that were obtained in grain cultivation. At best Columella provides a trustworthy figure for poor soils; at worst, his estimate is not reliable at all." Average wheat yields per year in the 3rd decade of the century, sowing 135 kg/ha of seed, were around 1,200 kg/ha in Italy and Sicily, 1,710 kg/ha in Egypt, 269 kg/ha in Cyrenaica, Tunisia at 400 kg/ha, and Algeria at