The researchers studied how much water different crops in Northern Shandong Province need during their growing seasons. They used a formula to calculate the water needs of the crops and found that winter wheat needs 491.2 mm of water, summer corn needs 371.0 mm, spring cotton needs 425.8 mm, apple trees need 666.8 mm, and Chinese chive needs 891.8 mm. They also calculated the crop coefficient for each crop, which tells us how efficiently they use water. Winter wheat has a coefficient of 1.32, summer corn has 1.34, spring cotton has 0.85, apple trees have 0.99, and Chinese chive has 1.33.