Crop Water Use Efficiency | Agriculture Optional Notes for UPSC PDF Download

Introduction

Crop or plant water use efficiency (WUE) quantifies how much crop or pasture material is generated for each unit of water accessible to the plant. In the context of dryland (rain-fed) cropping systems, this is typically measured as the kilograms of grain yield per hectare per millimeter of rainfall during the growing season, which typically spans from April to October.

Measuring crop water use efficiency

A well-recognized model for crop water use efficiency was developed by French and Schultz in 1984. According to this model, crops could potentially yield up to 20 kg of grain per hectare for each millimeter of rainfall, taking into account the evaporation of soil moisture. This essentially means that a crop can attain its maximum yield potential by utilizing 100% of the rainfall it receives. Recent studies indicate that modern high-yielding crop varieties, which have been bred more recently, are capable of achieving around 25 kg of grain per hectare per millimeter of rainfall. This level of efficiency is being realized in various large-scale farming scenarios.

Monitoring and Trends

Water use efficiency (WUE) can serve as a broad indicator of the overall health of the soil. It reflects the capacity of the soil to support plant water uptake and growth while also being influenced by climatic factors and agronomic practices, in addition to the inherent productivity potential of plant varieties. When WUE is low, assuming reasonable agricultural practices, it may suggest underlying soil limitations to productivity or a decline in soil quality.

WUE is not a definitive diagnostic indicator because a low WUE value could result from various soil and agronomic limitations. An upward trend in WUE typically indicates an improvement in addressing one or more growth limitations. A consistent or low WUE, especially when the value is relatively low, might suggest that existing limitations are not being addressed, or improved practices have not been adopted. A declining trend in WUE is likely to indicate worsening limitations to plant growth, some of which could be attributed to a decline in soil quality.

In South Australia, the water use efficiency of wheat has been assessed as a general measure of soil health in cropping areas from 1982 to 2020. This analysis used annual wheat yield estimates and rainfall data to estimate WUE by district and region. It has helped identify potential soil or agronomic constraints to production and opportunities to enhance productivity.

Wheat water use efficiency in South Australia was approximately 7 kg per hectare per millimeter in the 1960s and 1970s, followed by a steady increase during the 1980s and 1990s, leveling off at around 11 kg per hectare per millimeter in the 2000s. In the past decade, WUE has further improved to approximately 14 kg per hectare per millimeter.