they did everything together 
while farming,weaving.built canals for irrigation of crops,
and  also became landowners together these are some of the places they excelled together. thus they became good farmers
Too small, my answer was much better.
The Sumerians lived in the south of the Fertile Crescent in about 4000 BC. Most of them were farmers. Their land was the exact opposite of fertile (though the name of their place was Fertile Crescent!!!), which was very flat, barren and dry. And they did not even have good tools to cultivate crops. So, being a farmer was very hard to the Sumerian people. But, the Sumerian people were really very hard-working and had a good sense of unity in their work. In that way, working together in complete unity, they did very much work under the orders of their leader or king. The leaders told the people to dig canals for proper supply of water and proper irrigational system. They decided when to plant the grain and harvest it. They also kept records of each harvest. In this way, the Sumerians became very good farmers.