Soil management

Soil contains a huge number of very diverse living organisms such as worms, fungi and bacteria. Many of these organisms work for the benefit of agriculture by recycling organic water, cleaning pollution and transforming atmospheric dinitrogen gas into free fertilisers. So far soil organisms are underutilised because many organisms are not even identified, and their beneficial expertise is often unknown. Microbiologists Degrune et. al set up a new method that allows to distiguish microbial communities in soils cultivated with different cropping practices.

Organic producers in the United States would like to no-till, but are concerned about managing weeds without tillage.  Agronomist Randy Anderson shows that weeds can be controlled without tillage in experiments in the Great Plains of the USA. One favorable tactic is to include a 3-year interval of red clover in the rotation.  Red cover suppresses both annual and perennial weeds, and it can be converted to cropland by fall mowing in the 3rd year (Photo).  The complex rotation increases the impact of no-till on weed seed decay in soil and provide numerous opportunities for cover crops to replace tillage for controlling weeds.  These benefits suppress weed growth and interference such that organic producers may be able to continuously no-till in their farming systems.

Industrial monoculture is often leading to the depletion of soil life and quality as a result of intensive tilling. New advanced techniques such as no-till and strip-till farming allow to restore soil fertility in the long run. No-till farming increases soil water, soil organic matter and decreases soil erosion. In strip till the farmer tills only the portion of the soil that will contain the seed row. Islam et al. studied no-till strip farming of maize-soybeans rotations. They observed a 75% increase of maize yield, amounting to 18.4 tons per hectare, after 5 year of cultivation.

The area of agricultural land on saline soils is increasing as a result of climate change and more frequent droughts. Since salt at high concentration is toxic to most plants, cultivation on such soils is becoming more and more difficult and induces yield losses. There is therefore a need for strategies to grow plants on saline soils. Farooq et al. review the mechanisms of maize resistance under salt stress. They propose solutions such as the use of arbuscular mycorrhizal fungi to improve plant nutrition.

Industrial agriculture is known to decrease biodiversity and degrade soil structure. Agronomists Sánchez-Moreno et al. studied the impact of herbicides and soil management on nematodes – soil worms – and other soil life in Mediterranean areas. They found that soil life diversity is decreased by herbicides.

Most plastic products contain phthalic acid esters that end up polluting water and soil after plastic degradation. Indeed, phthalic acid esters are endocrine disruptors. China is one of the largest consumers of phthalic acid esters. He et al. review the contamination of soils by phthalic acid esters. Findings show that the levels of phthalic acid esters in chinese soils are higher than recommended limits, thus contaminating vegetables. The main sources of phthalic acid esters in soils are plastic agricultural films, municipal biosolids, agricultural chemicals and wastewater irrigation.

Global warming is partly due to intensive monoculture farming that burns soil carbon into carbon dioxide (CO₂), a greenhouse gas, which is then transferred to the atmosphere. Alternative agriculture pratices are therefore needed to preserve soil carbon. Agronomists Hu et al. found that wheat-maize intercropping with reduced tillage and stubble mulching decreased carbon emission by 10% and increased yield by 11% compared to conventional tillage.

Soils contain huge amounts of various living organisms such as worms, fungi and microbes. Those life forms play essential ecosystem services such as filtering water, removing pollutants and providing plant nutrients. However, the effect of soil biodiversity on ecosystem services is still poorly known. Lemanceau et al. show that preservation and valorization of soil biodiversity is a major challenge for agroecology. Their review highlights recent advances in the assessment of soil biological quality. Further research is needed to design decision tools that can be used by farmers to better manage soil biodiversity.

Industrial agriculture has strongly altered soil life, and, in turn, decreased fertility. Alternative practices such as conservation agriculture and organic farming could restore better conditions for soil organisms. Henneron et al compared the effect of 14 years of conservation agriculture, organic farming and conventional agriculture on soil organisms such microbes and worms. They found that conservation agriculture and, to a lesser extent, organic farming improved all soil organisms.

Soil living organisms are essential for food production by recycling organic matter and providing sustainable plant nutrients. Agricultural practices may degrade soil life, by actually precise knowledge on the impact of cropping is poorly known at the microscale, in micro- and macro-aggregates. The article by Constancias et al. reveals that cropping highly reduced bacterial density and diversity at the microscale, compared to bulk soils. The findings show that cropping practices that preserve aggregate stability should be favoured to preserve soil microbial diversity, and in turn fertility and food production.