Comparisons of Moisture and Energy Balance Components as Influenced by Two Row Orientations of Soybean.

Abstract

When a crop is grown in rows, the row direction influences the energy balance and moisture budget of the soil-canopy system of the crop. Attempts were made to compare energy balance and moisture budget of E-W row soybeans with those of N-S rows at partial cover during the summer of 1996. The energy balance and moisture budget were considered for the soil and canopy separately. Daily fluctuations and diurnal patterns of energy and water balance of field, soil and canopy were strongly influenced by row orientations. Average latent heat flux density (LE) observed in N-S row soybean field was 6.6% larger as compared to E-W row soybean field. Average ratios of -LE to net radiation (Rn) were found 0.85 and 0.87 for E-W and N-S rows, respectively. Soil heat flux (G) accounted for 14 to 20% of Rn for E-W rows and 6 to 9% for N-S rows. Soil surface net radiation (Rns) of E-W rows was about 25% larger than that of N-S rows. Latent heat flux from the soil (LEs) was about 13% larger in E-W rows as compared to N-S rows. The -LEs/Rns ratios often exceeded 1.0 in both the cases. The sensible heat flux from the soil showed a positive trend in both the cases indicating soil surface was absorbing convective heat. The -G/Rns ratios were found 0.41 and 0.26 for E-W and N-S rows, respectively. Average net radiation of E-W row canopy (Rnc) was 20% smaller as compared to N-S row canopy. Latent heat flux from the E-W row canopy (LEc) was 19% smaller as compared to N-S row canopy. The -LEc/Rnc ratios were found 0.80 and 0.79 for E-W and N-S rows, respectively. Sensible heat flux from the canopy showed negative trends in both the cases. Results suggest that only field energy balance measurements would not provide sufficient information on how energy balances of the soil and canopy are partitioned.