Under very dry condition

the winter wheat roots in cultivated soil layer withered in spring

the epidermis

except the vascular tissue

damaged. This showed that the roots lost their absorbing ability.The roots in deep soil layer have the absorbing ability because the deep soil layer is damper

but the water and nutrient that absorbed by the roots in deep soil layer can not meet the need of wheat growth and development.for the roots and nutrient in deep soil layer are less than those in cultivated soil layer.So

the yield was very low.After the rainfall in the turn of green stage and jointing stage

the damaged roots can not recover

but winter wheat has the ability of producing new secondary roots to recover its absorbing ability.In this stage

the root system had strong compensation absorbing ability.Thus

it is an effective measure to raise the effects of water and fertilizer on dryland winter wheat through applying nitrogen fertilizer in spring ram.