8. ENVIRONMENTAL EFFECTS OF ORGANIC, INORGANIC AMENDMENTS AND AGROCHEMICALS

8.1 INTRODUCTION

Over the past century humans have introduced a large number of chemical substances into the environment. Some are the waste from industrial and agricultural processes. Some have been designed as structural materials and others have been designed to perform various functions such as improving crop growth or killing pests and weeds. Obviously some chemicals are useful but many are toxic and their harm to the environment and our health far outweighs their benefit to society. We need to manage the risks better by only using chemicals, which are safe.

Agrochemical

—Any substance used in the management of an agricultural ecosystem, including fertilizers, pH-adjusting agents, soil conditioners, pesticides, and crop-growth regulators.

Fertilizer

—An agrochemical that is added to soil to reduce or eliminate nutrient-caused constraints to crop productivity. Fertilizers are substances that are added to farmlands to encourage plant growth and to increase crop yields.

Soil conditioners

—Substances added to soil to improve its aeration and water-holding capacity, with great benefits in terms of crop growth. Various organic compounds can be used as soil conditioners, but compost is the best. Materials used as soil conditioners include peat, livestock manure, sewage sludge, and even shredded newspapers

Pesticide

- Any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest. A pesticide may be a chemical substance, biological agent (such as a virus or bacterium), antimicrobial, disinfectant or device used against any pest.

Detrimental Effects of Agrochemicals on the Environment

The use of certain agrochemicals has also been associated with some important environmental ecological damages as outlined below:

1) Fertilizers:

i) Groundwater contamination: Excessive use of fertilizers can lead to the contamination of groundwater with nitrate, rendering it unfit for consumption by humans or livestock. Water containing large concentrations of nitrate can poison animals by immobilizing some of the hemoglobin in blood, reducing the ability to transport oxygen.

ii) Eutrophication: In addition, the run-off of agricultural fertilizer into streams, lakes, and other surface waters can cause an increased productivity of those aquatic ecosystems, a problem known as eutrophication. It starts by increasing the amount of phytoplankton in the water, this then blocks out the sunlight, which leads to plants being unable to photosynthesise, which in turn means that the fish and other creatures don't have anything to eat, which means they die and then in turn so do other animals that depend on them such as birds.

2) Pesticides: The use of pesticides raises a number of environmental concerns. Over 98% of sprayed insecticides and 95% of herbicides reach a destination other than their target species, including non-target species, air, water and soil.

i) Air pollution by pesticides

Pesticides can contribute to air pollution. Pesticide drift occurs when pesticides suspended in the air as particles are carried by wind to other areas, potentially contaminating them. Pesticides that are applied to crops can volatilize and may be blown by winds into nearby areas, potentially posing a threat to wildlife.

ii) Water pollution by pesticides

There are four major routes through which pesticides reach the water:

a) it may drift outside of the intended area when it is sprayed,
b) it may percolate, or leach, through the soil,
c) it may be carried to the water as runoff or it may be spilled, for example accidentally or through neglect.

d) it may also be carried to water by eroding soil.

There are some factors that also affect pesticide's ability to contaminate water and these include:

a) its water solubility,
b) the distance from an application site to a body of water,
c) weather,
d) soil type,
e) presence of a growing crop, and
f) the method used to apply the chemical.

iii) Soil pollution by pesticides

Many of the chemicals used in pesticides are persistent soil contaminants, whose impact may endure for decades and adversely affect soil conservation. The use of pesticides decreases the general biodiversity in the soil. Not using the chemicals results in higher soil quality with the additional effect that more organic matter in the soil allows for higher water retention. This helps increase yields for farms in drought years, when organic farms have had yields 20-40% higher than their conventional counterparts. A smaller content of organic matter in the soil increases the amount of pesticide that will
leave the area of application, because organic matter binds to and helps break down pesticides.