Early farming in river flood plains resulted in a more reliable harvest because of several reasons. what is not one of these reasons?

The correct answer is  River sediments deposited nutrients.
 Riverflood plains resulted in  more yields as crops were less dependent on rainfall and due to the availability of more workers at the river basin areas which had comparatively bigger populations. Natural fertilization also made a sedentary lifestyle possible enabling more people to settle

River sediments deposited nutrients.
Rivers sediments doesn't have to necessarily to always deposit nutrients An example is the civilization of ancient Egypt. It was indebted to river Nile and its dependable seasonal flooding. The rivers predictability and the fertile soil but not river sediments allowed the Egyptians to build an empire on the basis of great agricultural wealth.