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Less use of fertilisers boosts soils

Mwangi Mumero @PeopleDailyKe

Researchers from the International Centre for Tropical Agriculture (CIAT) in collaboration with their counterparts in the Kenya Agricultural and Livestock Research Organisation (Karlo) have found that use of industrial fertilisers and retention of crop residues have a huge impact in boosting soil microorganisms.

Their research work — carried out in Western Kenya and supported by GIZ, a German aid organisation—have also noted that less soil disturbance in tillage is also critical in promoting the proliferation of soil microbes.

Microbes play a key role in decomposing soil organic matter, and thus keeping more carbon in the soil. They also help recycle nutrients and supply plants with vital food, while keeping the soil structure stable.

“A handful of soil contains more microbes than the total human population on earth,” says Dr Gerrit Gerdes, country programme manager, GIZ western Kenya. Overall, organic farming is viewed as promoting proliferation of soil life and diversity, while industrial fertiliser is seen as an oppressor’ of soil life, simply supplying nutrients.

The researchers, however, discovered a combination of industrial fertilsers and crop residue retention in the farms plays a bigger role in stabilising soil microorganisms.

In the study spanning 13 years, researchers found that integrating application of fertilisers and residue retention in maize-soybean rotation systems favoured a high diversity of various functional groups of bacteria.

These include high diversity of nitrogen fixing symbionts, phosphorus solubilising microorganisms and organic matter decomposers. “What this means is that these microbes therefore play essential roles in nutrient cycling – nutrients that come from both manure and synthetic fertilisers,” said Job Kihara, one of the six other researchers in the team.

Removing either residues from a farmer’s field – or application of industrial fertilisers – as the only input on the farm, decreases microbial diversity and functions, the study noted.

In other words, a combination of both can have a more beneficial impact than either technique by itself. Application of nitrogen fertilisers alone for example reduced the population of some soil microbial communities like cyanobacteria and kribbella – another microbial species involved in nitrogen cycling in the soil.

Among the cropping systems, inter-cropping, which is commonly practised by farmers, promotes higher microbial populations, such as for nitrospira – a species involved in the nitrification process in the soil – compared to rotation systems.

Also, combined application of lime and Minjingu phosphate-rock, similar to treatments under poor management – no residues or manure applied – reduced the activities of enzymes involved in phosphorus mineralisation; an indication that such practices in isolation do not increase soil health.

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