Water management is most effective when combined with optimal use of inputs and good crop management. The efficiency of a limited resource is at its best when all other inputs are at their optimum, says a FAO report titled The State of Food and Agriculture 2020.
Improved water management should be combined with correct management of other inputs. Modern high-yielding crops are crucial in raising water productivity. During the Green Revolution, modern crop varieties, with increased irrigation and agrochemicals, played a major role in increasing yields of major crops. Soil nutrient status also has major effects on crop water productivity.
Sadras demonstrated this for wheat crops in the Mallee region, Australia, where water and nitrogen accounted for a proportion of the gap between attainable and actual water productivity. Several integrated approaches allow farmers, particularly on small-scale rainfed farms, to improve productivity sustainably. These combine best practices with improved soil and water management that intensifies production through integrated soil fertility management, greater water-use efficiency and crop diversity.
Some critical primary crop and nutrient management factors include:
- timely crop planting and harvesting to match rainfall, multicropping when possible to utilise soil moisture and recover soil nutrients, and shifting the planting season to periods of low evaporation;
- plant spacing and row orientation, involving optimum planting density (the amount of space between plants) and high stand uniformity;
- selecting crop varieties with high yield potential and/or that are resistant to drought and/or grow faster under canopy cover;
- spatial allocation and zone crop management, identifying and excluding fields that deliver consistently lower yields to help improve average crop water productivity;
- nutrient management, as soil nutrient status affects crop water productivity, weeding and pests. Conservation agriculture Conservation agriculture can improve water and nutrient efficiency by promoting minimum soil disturbance (i.e. no tillage), maintenance of permanent soil cover with crop residues and live mulches, and diversification of plant species.
Conservation agriculture has expanded rapidly, reaching about 180 million hectares across 79 countries. The main reasons include higher factor and water productivity; lower production costs and higher profitability; and greater yield stability.
In China, conservation agriculture has contributed to yield increases from 2 per cent to 8 per cent for wheat, maize and rice. In India, it has substantially reduced production costs for farmers and increased irrigation water productivity.
Conservation tillage can improve soil-water storage, soil quality and crop yield, and reduce evaporation. Livestock on improved pastures derived from crop–pasture rotations based on conservation agriculture produce more meat per unit of pasture and with less greenhouse gas (GHG) emissions.
The impacts on water productivity depend on context and effects on evapotranspiration and yields. Conservation agriculture may face challenges in sub-Saharan Africa and Southern Asia, where crop residues are used as livestock feed or household fuel.
Other challenges include increased weeds and additional labour when herbicides are not employed, affecting women in particular. The success of conservation agriculture often depends on identifying agroecological regions and soil types where it can be readily adopted. Developing site-specific packages and educating the farming community and general public about benefits will also help.
Conservation agriculture can also contribute to making agricultural systems more resilient to climate change. In many cases, it has reduced farming systems’ GHG emissions and enhanced their role as carbon sinks.
Climate-smart irrigation agriculture is another important option for adaptation to climate change. It focuses on improving productivity and profitability of existing irrigation, enhancing farmers’ resilience to climate change.
Box 1
The benefits of modern irrigation – evidence from China, India and the USA
In the Province of Hebei, China, subsurface drip irrigation has reduced evapotranspiration compared with flood and surface drip irrigation by 26 per cent and 15 per cent, respectively, increasing water productivity by 25 percent. It has further increased grain yield and biomass formation through lower evaporation, and can therefore be used to address water scarcity.
In India, field trials in 2012 and 2013 in Coimbatore City showed drip irrigation increased grain yields by almost 30 per cent, doubled water productivity and used 27 per cent less water relative to conventional rice production.There was also a 40 per cent increase in the return on investment. Another field study in the Sirsa district of Haryana State illustrated the economic benefits of drip irrigation, showing it was more cost-effective than furrow irrigation in cotton production, reducing cultivation costs by 25 per cent and generating water and electricity savings of 33 per cent. It also reduced weeding and soil erosion problems. However, a lack of subsidised equipment and farmers’ know-how has restricted access to this technology.
According to a study in California, USA, subsurface drip irrigation increases crop yield and water productivity through better water management and improved fertiliser control. Another study in San Joaquin Valley, California, showed the yield of tomatoes under drip irrigation was about 20 per cent higher than that under sprinkler irrigation for similar amounts of water. It also found that, depending on the difference in yield and interest rates, profits per hectare under drip irrigation were from US$ 867 to US$ 1493 higher than under sprinkler irrigation. However, little, if any, water saving per hectare is possible by converting to drip irrigation. Luhach et al encourage sprinklers in fruit production owing to their economic viability, reduced pressure on water resources, and lower operational and labour costs.
Box 2
Effect of crop management on evapotranspiration, yield and water productivity – evidence from Argentina and India
A study in Argentina analysed the response of maize yield, crop evapotranspiration and water productivity to reduced row spacing under different water and nitrogen regimes. Grain yield response to narrow rows (35 cm versus 70 cm) ranged from 0 to 23 per cent, higher for water limited rainfed crops and/or nitrogen-deficient crops (i.e. non-fertilised crops).
Narrow rows increased crop evapotranspiration during initial stages of growth by 8 per cent, while nitrogen fertilisation did not influence it. Reduced row spacing further increased water productivity for grain by up to 17 per cent. The effect was more pronounced when the crop was nitrogen-deficient and/or with water limitations, but negligible for fertilised and irrigated crops. Van Dam et al simulated crop growth at different sowing dates (between 10 November and 10 December) in Sirsa District, India. Early sowing increased grain yield and, combined with a small increase in evapotranspiration during growing, raised water productivity by 20 per cent.
Source: http://www.fao.org
