Soil properties

Soil is critical to life on earth. It comprises mineral particles, organic matter, water, air, flora and fauna. Soil formation is an extremely slow process, so soil is essentially a non-renewable resource and must be valued, respected and treated with great care. Agronomic techniques such as no-till and cover crops, which involve the use of non-selective herbicides like paraquat for weed control, can preserve and improve the quality of our soils.
The UN Food and Agriculture Organisation (FAO) held a forum in Rome to mark World Soils Day on 5 December 2014 and to launch the International Year of Soils. Speakers at the event emphasised the critical importance, complexity and fragility of this thin layer covering the earth.1
Soil degradation and agriculture
It takes 1000 years to form about three centimetres of topsoil and the planet is losing an area equivalent to 30 soccer fields every minute. About one third of all the world’s soil is now considered to be degraded.
Soil degradation is caused by a number of factors, most particularly erosion by water and wind. Farming and associated deforestation are by far the main causes of degradation (Fig. 1).
Paraquat’s distinctive behaviour in soil means that farmers around the world confidently use it to protect their crops. Paraquat provides fast broad-spectrum weed control only through foliar contact action. There is no crop damage via the roots or any effect on seed germination. Soil fauna and microorganisms are not affected and there is no leaching or run-off from the degrading paraquat residues reaching the soil.
This article explains the fate of paraquat in soil in relation to the implications for the environment and its role in raising agricultural productivity. Two inter-linked processes are fundamental to the overall fate of paraquat in soil: how it binds (adsorbs) to soil and how it degrades in soil.
Paraquat degradation
Paraquat’s distinctive behaviour in soil means that farmers around the world confidently use it to protect their crops. Paraquat provides fast broad-spectrum weed control only through foliar contact action. There is no crop damage via the roots or any effect on seed germination. Soil fauna and microorganisms are not affected and there is no leaching or run-off from the degrading paraquat residues reaching the soil.
A new in-depth feature article added to the Knowledge Bank explains the fate of paraquat in soil and what the implications are for the environment and paraquat’s role in raising agricultural productivity. 
 
Fate of paraquat in soil Soils can deactivate paraquat equivalent to hundreds to thousands of years of application Microorganisms can quickly degrade paraquat in solution Tiny amounts of paraquat are slowly released from soil particles, degrading so that residues plateau, but not enough to have deleterious biological effects Paraquat is deactivated on contact with soil, being very strongly bound to mineral particles and organic matter
Paraquat is used to control a huge range of weeds worldwide, but to control weeds effectively and sustainably it is important to understand them.
Why does a plant become a weed? How can different types of weeds be described? What are the features of weeds and the way they grow which can be targeted by herbicides for successful control? Why is paraquat such a useful tool for farmers?
What are weeds?
Weeds are usually described as unwanted plants.  Weeds grow on arable land which is waiting to be planted and then a new flush of weed seedlings emerge with the crop.  In perennial crops like fruit, vines, rubber and oil palm, weeds grow continuously with new growth prompted by the weather and changing seasons.
Weeds are unwanted for many reasons: They compete with crop plants for sunlight, water and soil nutrients, reducing yields and quality.
They may provide a habitat for pests and diseases from which these can attack the crop.
Large, climbing or spiny weeds can make it difficult to get into the crop for pest and disease control, fertilizer application, harvesting and other operations.
Paraquat and sustainable agriculture, by Richard H. Bromilow
In his paper “Paraquat and sustainable agriculture,” author Richard H. Bromilow studies the role paraquat plays in supporting sustainable agriculture around the world.
Abstract: Sustainable agriculture is essential for man's survival, especially given our rapidly increasing population. Expansion of agriculture into remaining areas of natural vegetation is undesirable, as this would reduce biodiversity on the planet. Maintaining or indeed improving crop yields on existing farmed land, whether on a smallholder scale or on larger farms, is thus necessary.
One of the limiting factors is often weed control; biological control of weeds is generally of limited use and mechanical control is either often difficult with machinery or very laborious by hand. Thus the use of herbicides has become very important. Minimum cultivation can also be important, as it reduces the power required to work the soil, limits erosion and helps to maintain the organic matter content of the soil.
This last aspect helps preserve both the structure of soil and its populations of organisms, and also sustains the Earth's soil as a massive sink for carbon, an important consideration in the light of global warming.
Integrated weed management and no-till are advanced agronomic tools with common aims to improve efficiency and profitabilty, while reducing the environmental impact of crop production. Although advanced in concept, these tools are straightforward and can be adapted for use in all cropping systems, from highly mechanised ones to subsistence farming, all around the world.
Tillage is a well proven means of controlling weeds, so are other methods good enough to use in an integrated approach to weed management in no-till systems? This article examines how farmers can reap the rewards of both techniques together.
Farmers around the world know just how hard it is to control weeds. They tend to come back with a vengance, especially when the many elements causing weed problems have not been appreciated and addressed. Aiming to manage weeds rather than control them is not only more realistic, but if Integrated Weed Management (IWM) is applied properly, it can reduce costs, protect the soil, and support pest and disease control.
No-till systems also provide economic and environmental advantages. However, in no-till, the traditional means of weed management by ploughing to prepare a field for cropping is not used. Plowing, even though it effectively removes weeds by burial, is costly, time consuming, and can cause soil erosion and compaction.
Will farming and soil quality collide?
World Agriculture and the Environment is an important new book addressing the fear that increasing demand for food and fiber is on a “collision course” with soil quality.
This article is in two parts. In Part One, some of the main issues discussed in the book are reviewed. Part Two then explains how more than 50 years of research and practical use have shown that controlling weeds with paraquat can help provide improved and sustainable crop management practices to improve soil quality.
Part One: What ‘World Agriculture and the Environment’ says
In World Agriculture and the Environment authorJason Clay (World Wildlife Fund-US vice president, Center for Conservation Innovation) reviews the production and environmental impact of 21 of the world’s major food commodities. The main threats to the environment posed by crops, fish and meat are identified and explored, as well as the trends that shape those threats.
Major Issues
Deactivation of the biological activity of paraquat in the soil environment: a review of long-term environmental fate. by Roberts TR, Dyson JS, Lane MC. In their paper Deactivation of the biological activity of paraquat in the soil environment: a review of long-term environmental fate,” the authors bring together several key environment studies on paraquat in order to analyze and assess its long-term environmental impact. They conclude that:
“These trials have demonstrated that the continued use of paraquat under GAP conditions will have no detrimental effects on either crops or soil-dwelling flora and fauna.”
Abstract:
Extensive long-term field studies confirm - and governments and regulatory authorities, worldwide, agree - that normal use of paraquat in accordance with the approved label instructions does not cause an unacceptable environmental impact.
These studies have shown that:
Paraquat is inactive in soil
When paraquat residues come into contact with the soil the paraquat active ingredient rapidly becomes adsorbed and strongly bound to clay and organic matter in the soil. It becomes biologically inert and as a result it cannot be taken up by plant roots or other organisms. Paraquat treated soils still maintain an active soil ecosystem with no adverse effects on soil microbes, microorganisms and earthworms. Paraquat cannot be released from the soil or re-activated by the application of water or other agrochemicals.
All agricultural soils, not only those with high clay content, have a high capacity to absorb paraquat.
Mr. Prasanna Srinivasan of New Dehli, India, is a recognized expert in the field of economics, policy and regulatory development and specializes in the impact of global environmental treaties on developing countries. Syngenta commissioned Mr. Srinivasan to provide a balanced assessment of the benefits and risks of pesticides in general and paraquat in particular. Mr. Srinivasan recently completed this review entitled, “Paraquat: A unique contributor to agriculture and sustainable development.
Please click on this link to download a copy of the review:
Paraquat: A Unique Contributor to Agriculture and Sustainable Development