They used a plow for the entire area even around the well - there was so little land that they there was not a single piece they could afford not to till. The giant is afraid the water from the well could turn the soil into gunk.

Kêng is composed of 耒 lei a plough-handle (itself composed of 木 mu wood and 丰 chieh rank weeds) as radical, with 井 ching a well as phonetic. It has been alleged that the latter is really a corruption of 田, in which case the whole character would be an ideogram.