Correct farming methods are found to raise food grain yields without pollution costs, says S.Ananthanarayanan.

The great increase in the world’s food demands in the last fifty years has been met by technology in farming, but at huge environmental cost. Use of artificial fertilizers has multiplied farm produce and is certainly a good thing. But the trouble is that much of the fertilizer used does not go to the plant, it runs off to pollute the land, rivers and ground water. And the production of fertilizer consumes energy, which leads to emission of CO2 and global warming.

But there is growing consciousness that output comparable with that of aggressive fertilizer use is possible with better cultivation methods and less fertilizer. Dr Fusuo Zhang, of the College of Resources and Environmental sciences, Beijing, with others from the same and other institutes in China and also from Stanford, report in the journal, Nature, the findings of a study, over four years, 2009 to 2012, with nearly 20,000 farmers in over 60 provinces in China. The study was of different farming methods which were implemented in experimental plots, with inputs and output scientifically monitored. The results, of integrated soil-crop system management, or ISSM, as a practical and effective farming technique is called, is found to be much better than traditional farming and almost as productive as respirce-intensive farming, but without the environment cost.

Fertiliser damage

What plants need to grow and produce grain is carbon, which is there as CO2 in the air, water and sunlight, and traces of nitrogen and phosphorus. But these traces are vital. Now, nitrogen is also, abundantly there, in the air, but this is nitrogen gas, in molecules which are inert and do not take part in any chemical reaction. What is needed for the plant is ‘reactive nitrogen’, or a form where the two atoms in the stable nitrogen molecule have been pulled apart, through the use of energy, and where the atoms, in the energetic state, are combined with other elements, and ready to react again, to get to a lower energy level. This kind of nitrogen is regularly created by energetic events like lightening in thunderstorms and to a large extent by microbes in the soil. Or, chemicals that release reactive nitrogen can be manufactured through energy guzzling industrial process.

The rapid rise in world population in the middle of the last century created huge demand for food grain, which was met partly by clearing forests to bring land under cultivation, irrigation, pesticides, but mostly by massive inputs of artificial fertilizer. While part of the fertilizer helped boost production, the bulk led to pollution of the land, loss of fish population, respiratory diseases and increased global warming by release of nitrous oxide, which is worse than CO2, into the atmosphere.

Fig 1 indicates the rise in the use of fertilizer, in China, since 1960.

Fig 2 brings out the disproportionate rise in fertilizer use since 1980. We can see that for less than 60% rise in food production, there was more than 200% rise in fertilizer use.

Business as usual, while world population and food demand continued to rise in the current century was hence clearly not sustainable.

Addressing the challenge

The paper in Nature describes the 4-year-long trials to examine the need for large fertilizer inputs and place on a firm footing alternate farming practices that may be as productive but cause less damage. The trials consisted of actually trying out four different farming procedures in large scale, realistic conditions with quantitative records, in the main agricultural belts in China, in respect of rice, wheat and maize, which account for almost all the grain harvested worldwide. The procedures tested were: 1. The normal practice of traditional farmers, 2. Improved methods, where science and technology helps overcome limitations of traditional methods, like timing of use of fertilizer and growing plants closer together, to increase yield, 3. Intensive farming, where the objective is maximize yield without considering costs and 4. ISSM, where the use of nutrients, including fertilizer, and water were optimized so that yields could be the best, with regard to the least environmental damage, based on the understanding of the relationship of the physiology of the plants and the ecology, the nutrient needs of high yielding plants and the processes that affected the availability of nutrients to the plant, or their release to the environment.

Detailed surveys were professionally carried out of a vast number of farmers, selected and randomised to accurately reflect actual levels of fertilizer use and grain yield. All published sources were also surveyed, of measures of the proportion of nitrogen lost, including as ammonia or nitrous oxide released to the atmosphere, to develop a model of how reactive nitrogen was released to the environment. All kinds of data were then collated, using the relationship between levels of nitrogen released in different ways and sources of nitrogen, and subjected to statistical analyses. Nitrogen not used, or the nitrogen surplus, could be worked out from the difference between the nitrogen used and what appeared in the plant that grew. The data showed, the study says, that the release of ammonia to the atmosphere was proportionate to the use of fertilizer, but the nitrogen surplus, release to nitrous oxide to the atmosphere and loss of nitrogen to the land and water increased faster and faster with increase in use of fertilizer.

Based on these relationships arrived at from the field, the team was able to work out the quantity of reactive nitrogen lost to the environment as kilograms per hectare or as kilograms for every tonne of grain yield, for each of the four methods of cultivation considered. And in a similar way, the extent of green house gases, that is CO2 in production of fertilizer and in transport, and methane, ammonia and nitrous oxide during plant fertilizing and growth, leading to global warming potential per hectare, were also worked out. The findings, in respect of nitrogen use are in fig 3.

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