Photo : Purabi Deshpande / Research Matters
When we think of nature at its vibrant best, our tendency is to think of tall trees, charismatic mammals, reptiles or a coral reef. The ground beneath our feet rarely makes the cut. A humble mixture of minerals, organic matter, gases, liquids, and thousands of organisms ranging from tiny bacteria to foot-long earthworms, the top soil nurtures life as we know it. It provides water and nutrients for plants to grow, making it critical for agriculture.
Better quality soil ensures better yields; and exactly for this reason, we have been manipulating the natural soil with the reckless use of chemical fertilizers that provide additional nitrogen, phosphorous and potassium (NPK), leading to over fertilization and diminishing yields. “The short-term increase of yield in response to added chemical fertilizer was encouraged previously to gain food self-sufficiency in developing countries like India. However, continuous use of chemicals in the intensive (aka conventional) farming system also caused slow down (or fatigue) in productivity because of a declining response to applied chemical fertilizers”, points out Dr. Debjani Sihi, a researcher at the University of Maryland Center for Environmental Science, USA.
In times like this, our best bet lies in organic farming -- a system of farming that does not use genetically modified (GM) seeds, synthetic pesticides or fertilizers. “Organic farming aims to attain long-term sustainability since it is based on ecologically sound practices to provide nutrients for crop growth. Thus, in the long term, it ensures productivity gains by improving soil health”, adds Dr. Sihi, who along with researchers from the Indian Agricultural Research Institute, New Delhi, the National Centre of Integrated Pest Management, New Delhi and the University of Florida, USA, has evaluated the impact of organic vs. conventional cultivations of basmati rice on soil health.
The results of the study, published in the Journal of Plant Nutrition and Soil Science, point out that in the long term, organic farming methods improve physical, chemical, and biological indicators of soil health.
The researchers conducted the study in 14 basmati rice fields in Kaithal district of Haryana, during Kharif (rainy) season of 2011. Seven of these fields were certified organic fields and others used conventional agriculture practices. “We chose basmati rice because of its high importance in international trade due to its fragrance (or aroma) and grain quality. India is the largest producer and exporter of basmati rice with about two-thirds of the production being exported”, says Dr. Sihi.
In the certified organic fields, the farmers used farm yard manure and decorticated neem cakes as fertilizers along with green manure crops incorporated into the soil in alternate years. Chemical fertilizers like urea, diammonium phosphate and muriate of potash were used in conventional farming fields. The researchers then analysed the various physical, chemical and biological properties of the soil in both the fields and its long-term and short-term effects.
The results of the study pointed out that the physical properties of the soil like the weight of the dry soil per unit volume and the water holding capacity improved after long-term applications of organic manure as opposed to chemical fertilizers. In addition, the soil pH was almost neutral, increasing the availability of major and micronutrients in the soil. Electrical conductivity, or the amount of salts in the soil was 26% lower in organic fields as compared to conventional fields and enzyme activities were 28 - 42% higher, thus helping nutrient cycling. In addition, the short-term replacement of chemical fertilizers by organic manure also showed significant impact primarily on soil enzyme activities and on organic matter content and nutrient availability of soil.
This holistic study stands out from the others since all the ‘organic’ methods used were following the International Federation of Organic Agriculture Movements (IFOAM) principles and studies both the short term and long-term effects of such practices on soil health. “We have proved that the buildup of soil organic matter is the key for enhanced nutrient cycling in organic farming system. Further, we also evidenced that biological and physicochemical soil fertility (aka soil health) are interdependent, however, the sensitivity of these indicators also depends on the timeframe of the study”, says Dr. Sihi.
As Dr. Sihi points out, ‘sustainable farming’ and ‘organic farming’ share a common philosophy of growing food without depleting natural resources and hence studies in these fields are more important than ever. “Findings of our study indicate that biotic and abiotic interactions in the soil were fostered under organic farming practices, which could facilitate nutrition for growing crops. Studies like ours highlight the fact that sustainable use of soil (and environmental) resources is necessary to obtain food security for our future generation”, she signs off.