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Strengthening soil microbes to replace fertilizers.

A collaborative study by scientists from the Jawaharlal Nehru University, Delhi University, Indian Agricultural Research Institute and National Research Centre for Plant Biotechnology shows how genetically modified soil micro-organisms can help restore nutrients in the soil to increase crop yield.

A healthy human diet consists of different nutrients that we get from different foods; vegetables and fruits give us vitamins, foods made from grains, like bread give us carbohydrates, pulses and meat give us protein and so on. An absence of a type of food from our diet for a long time can lead to malnutrition. Like humans, plants also need certain nutrients to grow optimally. Agricultural yield can be affected adversely if the soil the crops are being grown in is nutrient deficient.

The use of synthetic fertilisers ensures that the nutrients that plants need in large quantities like nitrogen, phosphorus and potassium, also called macro-nutrients, are added to the soil. But in the field, plants can only utilise a portion of the fertilizers added, the unutilized fertiliser subsequently causes a lot of environmental problems. To forgo the use of synthetic fertilizers, the use soil bacteria that can convert atmospheric nitrogen to nitrates and nitrites has been suggested. But the naturally occurring wild type nitrogen fixing bacteria have much lower efficiency compared to synthetic fertilizers.

In their recent study the researchers have used the diazotroph Azotobacter chroococcum, which is commonly found in neutral or basic soils. To improve the nitrogen fixing ability of the bacterium the scientists modified the genes involved in the nitrogen fixing mechanism of the bacteria. Knocking out a part of the negative regulatory gene nifL while simultaneously expressing the gene nifA, a positive regulatory gene.

Conducting experiments with wheat inoculated in the modified bacteria, in pots as well as the field, the researchers observed that the yield increased by almost 60% compared to the control crops. When urea was introduced to the soil, as it would be through fertilizers in a field, the researchers displayed that the inoculated wheat used ~85kg less urea than the usual ~257 kg urea per hectare. Additionally, there was no negative impact seen on the other soil microbiota due to the presence of the genetically modified Azotobacter chroococcum.

In India, wheat is cultivated in ~27 million hectares. Using these bacteria as biofertilizer, millions of rupees can be saved by cutting down on urea consumption, while the detrimental environmental effects of synthetic fertilisers can also be reduced.