Plants grow in a soil food web, fed by the biological activity of tiny living microorganisms in soil matter. Plant nutrition is created by soil nutrition. Fertilizer feeds either plant roots or the soil's biological processes, depending on its chemical or organic content. Fertilizer sciences seek ever more intricate understanding of the interaction of chemicals and soil biology.
Plant nutrition refers to a plant's need for and use of biological chemicals in soil, water and air. Plants need seventeen elements to grow and thrive. They absorb carbon, hydrogen and oxygen from air and water and the remaining fourteen elements must be available in soil, according to Utah State University. When soil is deficient in any of the fourteen nutrients, fruits and vegetables grown on it will be nutritionally deficient.
Fertilizer is material added to soil to enhance plant nutrition; soil amendments improve its fertility. Fertilizer can be synthetic or natural. In the mid-twentieth century, scientists developed chemical, or synthetic, fertilizer as a by-product of the Haber-Bosh process of creating liquid ammonia from air. Natural, or organic, fertilizer products are derived from natural sources. Chemical fertilizer is absorbed directly through plant roots. Natural fertilizer increases the biological activity in soil, which, in turn, enhances plant nutrition.
"Synthetic fertilizers have dramatically increased food production worldwide. But the unintended costs to the environment and human health have been substantial," according to Mark Schwartz, discussing research by Stanford University's Woods Institute for the Environment. The science of fertilizer development has turned its focus to global pollution problems created by release of excessive fertilizer-created nitrogen into the atmosphere. Other problems include topsoil erosion, soil fertility depletion and contaminated groundwater.
Cottonseed meal, feathermeal, seaweed, fish waste, animal manure, bone and blood meal, mined rock powders and alfalfa meal are all used in making organic fertilizers, according to Colorado State University Extension. Soil microbes ingest these materials and slowly release nutrients into the soil. Beneficial microorganisms help break down organic matter, making nutrients more available for plant nutrition, in a process called nutrient transfer. Breaking down organic material creates humus, which increases soil's water absorption.
The International Fertilizer Association recommends using a combination of organic materials and synthetic fertilizer to enhance productivity and plant nutrition. Scientists at the Woods Institute for the Environment, recommend moderated use of fertilizer for plant nutrition in areas such as sub-Saharan Africa, and reduction of use in countries such as China, where use of chemical nitrogen fertilizers in China increased 271 percent between 1977 and 2005.