Conservation agriculture for sustainable intensification of rainfed semi-arid tropics

Abstract

In rainfed semi-arid tropics increasing variability in rainfall, temperature extremes, land degradation and declining soil fertility, runoff, etc., are major threats for crop production which leads to low productivity and ultimately food security. The anthropogenic activities and agricultural practices like intense tillage, mono cropping, residue burning are the major causes affecting agricultural productivity. Conservation agriculture (CA) practices with three principles: no tillage, permanent soil cover, and appropriate crop rotation known as a set of adaptive agricultural systems is a panacea for this regions. CA was adopted in 36 countries in 2008/09. The area spread was 53, 77, 102 countries in 2013/2014, 2015/2016 2018/2019, respectively, which indicates rapid adoption/ expansion of CA in many countries of the world, namely, USA, Brazil, Argentina, Australia, Canada, China. Astonishingly, the global area under CA has increased @ 10 million ha per year since 2009. The CA spread in rainfed area was higher in many countries but the adoption rate in rainfed regions was lower in south Asia. CA is considered as a sustainable practice with the potential to maintain or increase crop productivity, profitability, environmental quality and ecosystem services. It typically improves soil quality. Moreover, CA practices increase water infiltration, moisture conservation, reduces soil loss and runoff. This reduction in runoff reduces the surface transport of nutrients like nitrate and phosphorus from agricultural fields and the eutrophication of water bodies, otherwise in conventional tillage leaching of nitrate to groundwater can potentially increase. Hence CA play a crucial role for land degradation neutrality, achieve sustainable development goals and ecosystem services. CA has been proposed as one of the components in climate-smart agriculture, owing to its reduced period to seed/plant next crop, reduced soil disturbance and lower fossil fuels consumption. Therefore, compared to the conventional tillage (CT), CA has a greater potential for soil C sequestration, favors higher soil biodiversity, lowers greenhouse gasses emissions, which helps it to be climate resilient technology. However, effect of CA on crop productivity, soil quality is highly variable and is dependent on several factors like soil, climate, duration of the study, and management practices. Crop residues plays a key role in CA to improve overall soil health, and ultimately improves crop productivity and sustainability. However, weed control, herbicide resistance, and weed shift under residue retained fields is a major challenge. In spite of numerous benefits, few vital constraints in the form of huge weed pressure in the initial years and rapid shift to perennial and difficult-to-control weeds, unavailability of scale appropriate seeder machines, lower availability of crop residues either due to low production or competing demands, termite infestation, etc., hinder adoption of CA among the farmers. Hence, profound technical/ scientific institutional support and encouraging government policy are of utmost requirement for wider adoption of CA. In this review, various aspects of CA relating to crop productivity, soil, and environment have been highlighted and discussed with a scientific background. This systematic review of agronomic, economic, soil fertility, ecosystem services with medium- and long-term adoption of CA in different systems and the bottlenecks of adoption in semi-arid tropics (SAT) conditions helps in better understanding by the extensionists, scientists and policy makers which is needed for wider adoption of CA in the region.