Practice of leaving the stalks of crops in the ground to anchor topsoil

This method is called no-till.

Explanation:

No-tillage is a conservationist cultivation technique where planting is done without the steps of conventional tillage and harrowing. In this technique, it is necessary to keep the soil always covered by growing plants and plant residues. The purpose of this cover is to protect the soil from the direct impact of raindrops, surface runoff and water and wind erosion. No-tillage can be considered as a minimum cultivation modality, since soil preparation is limited to the sowing furrow, sowing, fertilizing and eventually applying herbicides in a single operation.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)