Assessing water use effeciency and carbon sequestration potential of different wheat (Triticum aestivum) genotypes.

Abstract

Poor soil fertility status and limited water availability have been identified as two of the major constraints to crop production in South Africa. Under these conditions, growing crop genotypes that will sequester more carbon into the soil and be more water use efficient is crucial to improve crop production thus alleviate food insecurity. The aim of the study was to assess water use efficiency and carbon sequestration potential of different wheat genotypes. The experiment was set up under field and greenhouse conditions using 100 wheat genotypes from CIMMYT. These were grown at 25% (water-stressed) and 75% (non-stressed) field capacity (FC) using an alpha lattice with 10 blocks and 10 genotypes per block. Treatments were replicated twice in the field and three times in the glasshouse. After harvest the 10 best wheat genotypes were separated into roots and shoots, their chemical composition was analysed prior to the incubation experiment. About 0.25 g each of wheat root (RT) or shoot (ST) of the selected wheat genotypes were thoroughly mixed with 100 g of soil then transferred into an air tight PVC pot. NaOH solution was also placed inside the incubation pot to trap CO2 released during decomposition, and this was measured on day 0, 7, 15, 23, 31, 39, 47, 55, 63, 77, 91,105, and 120 of incubation. The results from the field and glasshouse experiments showed that average wheat grain yield (GY) varied from 326 g m-2 to 2062 g m-2, shoot biomass (SB) ranged from 1873 g m-2 to 3726 g m-2 while total plant biomass (PB) ranged from 2992 g m-2 to 6289 g m-2. Grain carbon stocks (GCS) averaged 132 g C m-2 and 167 g C m-2 in the glasshouse under stressed and non-stressed conditions, respectively. The total plant carbon stocks (PCS) ranged from 691 g m-2 to 3093 g m-2 (i.e. 348% difference) in the glasshouse, while they ranged from 835 g m-2 to 4016 g m-2 (i.e. 381% difference) in the field. Water use efficiency for grain yield production (WUE-GY) ranged from 0.12 g m-2 mm-1 to 2.10 g m-2 mm-1 (i.e. 18 fold increase) in the glasshouse under stressed conditions while it was 0.57 g m-2 mm-1 to 4.01 g m-2 mm-1 in

the field under stressed conditions. WUE components varied amongst wheat genotypes. LM75 exhibited higher WUE-GY under stressed conditions while genotypes LM48 and LM47 exhibited lower WUE-GY under non-stressed conditions. LM75 was also ranked the best genotype for WUE-PCS while BW162 was ranked the best genotype for WUE-RCS. In the incubation experiment the shoot treatments evolved higher net CO2-C compared to root treatments. Net CO2-C was highest within the first two weeks and declined with time. Amongst the root treatments, BW140 RT evolved the highest net CO2-C (86.6 mg CO2-C kg-1 soil), while LM70 RT evolved the lowest (48.8 mg CO2-C kg-1 soil). In shoot treatments BW162 ST and BW140 ST evolved the highest net CO2-C with average values of 218.7 and 223.8 mg CO2-C kg-1 soil respectively. Comparing all the 10 treatments LM70 RT evolved the lowest while BW140 ST and BW162 ST had the highest net CO2-C. The findings revealed that variability in storing C under different scenarios of water availability exists among the wheat genotypes studied. Also, the residues of different wheat residues exhibit potential of sequestering more C into the soil thus improve soil fertility.