1.3 Differential response of cereals and legumes to drought and salinity stress

Abiotic stresses (mainly drought and high soil salinity) are the major cause for the reduction in crop biomass and yield worldwide, especially in the SAT. Generally, Cereals are relatively better equipped to tolerate those stresses than the legumes, partly due to the carbon pathway differences between these two crop groups. Data collected using destructive measurements showed that under terminal drought the reduction of shoot biomass production in legumes can reach 50% especially in groundnut. In cereals, shoot biomass reduction is hardly above 40%.

Depending on the level of stress, both legumes and cereals may suffer from yield losses to a larger extent than shoot biomass reduction, however, in some cases, a better partitioning can help in a better yield. For example, reduction of chickpea seed yield due to terminal drought was recorded to be 26 to 61 % and the shoot biomass at maturity to be 31 to 63 % during three years of study using a large number of germplasm accessions. Whereas, the haulm yield of groundnut was reduced to 24 and 23% while the pod yield by 47 and 37% in the two years of field experimentation.

At a salinity level where the legumes would be completely dead, cereals like pearl millet and sorghum can thrive and be productive. However under salinity the larger adverse effect is on the reproductive growth than on the vegetative growth. Salinity affects plant growth and also equally the partitioning leading to a greater loss in seed yield. Reproductive biology is known to be more affected leading to greater yield damage. The partitioning to the root system plays a key role in tolerance to both drought and salinity.

1.4 Monitoring crop growth and productivity using remote sensing and GIS is key

The traditional approach of estimating the effect of a given abiotic stress on crop growth and productivity is becoming obsolete because of various reasons related to precision and up­scaling. Remote sensing data provide a complete and spatially dense observation of crop growth. This complements the information on daily weather parameters that influence crop growth. RS-crop simulation model linkage is a convenient vehicle to capture our understanding of crop management and weather with GIS providing a framework to process the diverse geographically linked data. Currently RS data can regularly provide information on regional crop distribution, crop phenology and leaf area index. This can be coupled to crop simulation models in a number of ways. CSM-RS linkage has a number of applications in regional crop forecasting, agro-ecological zonation, crop suitability and yield gap analysis and in precision agriculture.

In future the RS-CSM linkage will be broadened due to improvements in sensor capabilities (spatial resolution, hyper-spectral data) as well as retrieval of additional crop parameters like chlorophyll, leaf N and canopy water status. Thermal remote sensing can provide canopy temperatures and microwave data, the soil moisture. The improved characterization of crop and its growing environment would provide additional ways to modulate crop simulation towards capturing the spatial and temporal dimensions of crop growth variability.