Evaluation of the effects of nutrient management on grain yield, quality, and rheological properties of common wheat varieties (Triticum aestivum L.)

The rapid rate of population growth, extreme drought, heat waves, conflicts, and pandemics are pushing food production under strong pressure. As a result of this situation, in the next years, it is expected to have the food demand around 60 to 70% higher from the current level. At the same time, the input resource is going to be limited, contributing to the slowdown of agricultural productivity and production, mainly in developing countries. Global food demand depends on achieving sustainable cereal production, particularly rice, wheat, and maize. Widely adapted climate-resilient germplasm, and appropriate agronomic and resource management play a prominent role in sustainable crop production. Globally, the viability of limited genotypes and nutrient management, among other major challenges, must be addressed if the farmers have to improve their crop production leading to an increase in their profits, and livelihoods and fulfill the food needs of the consumers. In this research, the effects of nutrient management as a function of climate and soil variability were evaluated on common wheat varieties, through a number of experimental trials, in order to determine the cost-effectiveness of fertilization strategies along with high-yielding wheat varieties, that could contribute to crop productivity, increase quantity and quality and increase the farmer economic profitability. - The objective of Chapter 3.1 of this research is to evaluate the effects of two seeding density (SD), three nitrogen levels (NL), and two sulfur levels (SL) fertilization towards improving the grain yield (GY), rheological characteristics, and asparagine (ASN) content of 14 ‘old’ common wheat varieties. The results showed that SL and SD treatments significantly increased grain yield (GY) without decreasing the protein content (PC), while NL significantly increased the PC without affecting GY. The dough strength (W) increased significantly with increasing SL and NL but was significantly reduced with increasing SD. Asparagine (ASN) significantly increased by 111% as the NL fertilization increased from 35 to 135 kg ha−1, while ASN significantly decreased (85.1%) with the SL treatment. The findings show that 135 kg N ha−1 combined with 6.4 kg S ha−1 can improve the performance of ‘old’ wheat wholegrain flours while maintaining the ASN as low as possible. 2 - The objectives of Chapter 3.2 of this thesis were aiming to (1) evaluate the impact of soil and climate on the response of winter wheat to nitrogen (N), and phosphorus (P) fertilizations; (2) quantify the specific N and P response of winter wheat for different ACZs; and (3) determine the economical application rates of N and P for the economic benefit of farmers for each considered ACZs. This trail examines the effects of nitrogen levels (NL) at 35.28, 65, 95, and 120 kg N ha-1 and phosphorus levels (PL) at 0, 50, 70, and 90 kg P2O5 ha-1 , respectively, in four locations (L) for two growing seasons (GS), on both yield and quality characteristics of winter wheat. The result showed that soil pH was the main environmental parameter affecting straw yield (SY), grain yield (GY), protein content (PC), and protein yield (PY). Winter wheat SY, GY, PC, and PY increased significantly (p < 0.05) with PL rates up to 50 kg P2O5 ha-1 and with NL rates up to 120 kg N ha-1 . NL was the most important parameter in determining PC, thus showing potential for further improvement in N management. The highest marginal rate of return was used as an index for the farmers to accept site-specific N and P fertilizer recommendations. - The objective of Chapter 3.3 of this study aimed to evaluate the yield stability and agronomical traits of 33 common improved wheat (Triticum aestivum L.) varieties (V) under six environments (E), (three-locations x two-growing seasons) in Afghanistan. The combined ANOVA analysis showed that the variation due to the interaction of E x V for GY, SY, and HI was significantly larger compared to the main factor effect, environment, and variety; but the contribution of E x V for TKW and PH was smaller than the main factors. However, as average G09 showed the highest GY, followed by G31, G28, G15 and G04, whilst G31 showed wide stability, followed by G04, G15, G09, G25, in decreasing order, respectively. Interestingly, the 5-top superior stable varieties were also associated with higher GY, while G03, G01, G21, G18, and G02 varieties were identified as the most unstable with the poorest GY. Concerning locations, varieties G24, G29, G25, G15, G04 in BLK, G15, G09, G04, G23, G22 in HLM, and G31, G09, G32, G28, G27 in NGH location were identified as stable with higher GY performance. Moreover, results indicated that the highest grain yield was obtained by varieties that were grown in NGH while the lowest yield was obtained in HLM. - The objectives of this study were to (1) quantify the effect of soil and climatic parameters on yield and quality of wheat (2) investigate the response of different wheat varieties to different N and P fertilization rates under specific climate conditions, toward to improve the yield and quality of wheat in Afghanistan. Three wheat varieties (DLN7, ZRDN, and 3 KBL13), three phosphorus levels (PL) at 60, 90, and 120 kg P2O5 ha 1 , and three nitrogen ratios (NP) at 1:1, 1.25:1, and 1.5:1, respectively, in four locations (L), were evaluated. Soil pH was the main environmental parameter affecting grain yield (GY), straw yield (SY), protein yield (PY), and starch yield (STY) similar to PL and NP management. The higher average GY, straw yield (SY), and STY were obtained by DLN7, followed, by KBL13 and ZRDN for all Ls, but statistically, no significant differences occurred between DRL7 and KBL13. Moreover, as PL increased, GY, SY, PY, and STY increased significantly in four Ls. In addition, PL significantly affected protein content (PC), gluten content (GC), and dough strength (W). NP was the most important factor to improve PC, GC, and PY. Starch (ST), STY, and amylopectin (AP) increased significantly with increasing PL, but the amylose to amylopectin (AM:AP) ratio was significantly reduced as PL increased. On the contrary, AM:AP increased significantly with increasing NP ratios, but ST and AP were significantly reduced as the NP ratio increased. The findings show that at NP1/PL120, GY, SY, ST, and AP were improved significantly; while at NP1.5:1/PL12, PC, and GC were significantly improved. In conclusion, the results of this thesis proved that the wheat yield, quality characteristics, and rheological properties of wheat were sustainably affected by climate, soil variability, and fertilization factors. However, this result showed that to sustainably boost wheat production, the farmers need to follow proper nutrient management based on various climate zones and soil fertility. Also, the selection approach of high-yielding and stable wheat varieties based on specific agro-climatic zones can assure wheat production and farmer economic benefits, without affecting environmental pollution.