Extract the answer to the question from the following context. Question: How was the land kept fertile while the warriors were fighting? Context: In the late 14th century, in the Grand Duchy of Lithuania, Vytautas the Great reformed the Grand Duchy's army: instead of calling all men to arms, he created forces comprising professional warriorsbajorai ("nobles"; see the cognate "boyar"). As there were not enough nobles, Vytautas trained suitable men, relieving them of labor on the land and of other duties; for their military service to the Grand Duke, they were granted land that was worked by hired men (veldams). The newly formed noble families generally took up, as their family names, the Lithuanian pagan given names of their ennobled ancestors; this was the case with the Gostautai, Radvilos, Astikai, Kesgailos and others. These families were granted their coats of arms under the Union of Horodlo (1413).
worked by hired men