Estimation of net rice production through improved CASA model by addition of soil suitability constant (hα)

Abstract

Net primary production (NPP) is an important indicator of the supply of food and wood. We used a hierarchy model and real time field observations to estimate NPP using satellite imagery. Net radiation received by rice crop canopies was estimated as 27,428 Wm-2 (215.4 Wm-2 as averaged) throughout the rice cultivation period (RCP), including 23,168 Wm-2 (118.3 Wm-2 as averaged) as shortwave and 4260 Wm-2 (34.63 Wm-2 as averaged) as longwave radiation. Soil, sensible and latent heat fluxes were approximated as 3324 Wm-2, 16,549 Wm-2, and 7554 Wm-2, respectively. Water stress on rice crops varied between 0.5838 and 0.1218 from the start until the end of the RCP. Biomass generation declined from 6.09-1.03 g/m2 in the tillering and ripening stages, respectively. We added a soil suitability constant (hα) into the Carnegie-Ames-Stanford Approach (CASA) model to achieve a more precise estimate of yield. Classification results suggest that the total area under rice cultivation was 8861 km2. The spatial distribution of rice cultivation as per suitability zone was: 1674 km2 was not suitable (NS), 592 km2 was less suitable (LS), 2210 km2 was moderately suitable (MS) and 4385 km2 was highly suitable (HS) soil type with hα ranges of 0.05-0.25, 0.4-0.6, 0.7-0.75 and 0.85-0.95 of the CASA based yield, respectively. We estimated net production as 1.63 million tons, as per 0.46 ton/ha, 1.2 ton/ha 1.9 ton/ha and 2.4 ton/ha from NS, LS, MS and HS soil types, respectively. The results obtained through this improved CASA model, by addition of the constant hα, are likely to be useful for agronomists by providing more accurate estimates of NPP.