IMPROVING SORGHUM [Sorghum bicolor L. Moench] PRODUCTIVITY THROUGH SEED PRIMING, SOIL MOISTURE CONSERVATION, AND NUTRIENT MANAGEMENT IN SEMI-ARID AREAS OF EASTERN ETHIOPIA

Abstract

Sorghum [Sorghum bicolor (L.) Moench] is an important food crop cultivated in arid and semi-arid regions of Ethiopia in general and East Hararghe Zone in particular. However, the productivity of the crop is low due to limited and erratic rainfall, low soil fertility, and traditional farming practice. Therefore, effects of seed priming, and combined application of in-situ moisture conservation and nutrient management on sorghum productivity were investigated during 2014 cropping season in semi-arid areas of East Hararghe. Seed priming experiments were carried out under lab and field to evaluate the effects of priming on germination and seedling vigor, stand establishment, growth and yield of sorghum. The treatments for lab experiment consisted of three priming media [distilled water, Zn (0.2 g L-1 ZnSO4) and N (9 g L-1 urea)], five priming durations (0, 5, 10, 15, and 20 h), and six sorghum varieties (Abshir, Dekeba, Macia, Meko-1, Melkam, and Teshale). The results showed Zn primed seeds followed by N for 10 h priming duration recorded the highest improvements in germination percentage (6%), germination-index (8.4%), mean germination time (MGT) (4%), seedling-length (SL) (12.5%), seedling-dry-weight (SDW) (26.5%), seedling-vigor-index-1 (SVI-1) (33%) and seedling-vigor-index-2 (SVI-2) (49.7%) as compared to unprimed seeds. Likewise, variety Melkam with 10 h priming recorded the highest values of MGT, FGP, GI, SL, SDW, SVI-1, and SVI-2 that were higher by 7, 7.7, 4, 13.6, 30, 38, and 59% of unprimed seeds, respectively. Among the varieties studied, the three best performed varieties Dekeba, Melkam, and Teshale were used for farther assessment of seed priming media effects on stand establishment, growth, and yield of sorghum at Babile and Errer. The experiment was laid in randomized complete block design with tree replication of treatments consisted of three varieties (Dekeba, Melkam, and Teshale) and three priming media (water, Zn, N) and unprimed control. The results revealed that stand counts were significantly (P < 0.01) affected only by priming media, although the differences among priming media were non-significant. As compared to unprimed seeds, hydropriming had increased the plant stand by 10% and 16% at the period of establishment and maturity, respectively. The main effects of location, variety, and priming media significantly influenced the mean flowering and maturity time of sorghum. The zinc-primed seed was the fastest to emerge (5.4 days) followed by N, while unprimed seeds took the longest time (9.6 days). Likewise, varieties Melkam and Teshale, respectively, were the fastest to emerge (6.75 days) and mature (108.7 days). Variety Melkam took the shortest time (56.25 days), while variety Dekeba took the longest time to 50% flowering (62.2 days), both from Babile site. Similarly, Zn and N priming at Errer took the shortest time to 50% flowering, while unprimed seeds at Babile took the longest time to 50% flowering (62.2 days). The interaction effects of location  variety and variety  media on plant height were significant (P < 0.05). Variety Teshale from Errer was the tallest plant (169.5 cm), while variety Dekeba from Babile was the shortest plant (141.25 cm). Similarly, the N and Zn-primed seeds of variety Teshale was the tallest, while unprimed seeds regardless of variety were the shortest plants. The main effects of location, variety, and priming media were significant on leaf area index (LAI), while the interaction effect was not significant. The leaf area index recorded from Errer (3.73) was higher than xviii Babile. Likewise, variety Teshale (3.67) and N-primed seeds (4.1) recorded the highest LAI, while lowest LAI was from unprimed seed (2.84). The interaction effect of variety and priming media on panicle weight was significant (P < 0.05) where variety Melkam had the highest panicle weight (82.2 g) with Zn priming while the lowest panicle weight (71.5 g) was for variety Dekeba in unprimed seeds. The interaction effect of location and variety on thousand-kernel weight, grain yield, and aboveground dry biomass yield were significant. The highest 1000-kernel weight (28.02 g) was recorded from Babile for variety Melkam while the lowest (26.43 g) was from Errer for variety Teshale. Similarly, the highest grain yield was recorded from Errer for varieties Melkam and Teshale, while the lowest grain yield was from Babile for varieties Melkam and Dekeba. On the other hand, the highest (9420.4 kg ha-1) and the lowest (9031.6 kg ha-1) aboveground dry biomass yields were recorded from Errer for varieties Teshale and Dekeba, respectively. Another field experiment also conducted to investigate the effects of combining in-situ moisture conservation and nutrient management on soil moisture content, plant growth, yield components, yield, water use efficiency, and nitrogen uptake of sorghum. The experiment was laid out in split-plot design and treatments were replicated three times. Treatments comprised flatbed and tied ridge as main plot and nutrient amendments as subplot factors. Nutrient amendments comprised unfertilized control, 46 N/10 P kg ha-1, 5 t FYM ha-1, 23 N/5 P kg + 2.5 t FYM ha-1, 46 N/10 P kg + 2.5 t FYM ha-1 and 23 N/5 P kg + 5 t FYM ha-1]. The results of soil and water management study showed that the combining of in-situ moisture conservation and nutrient application had significantly affected the growth and yield of sorghum. The tallest plant was from tied ridges amended with 46 N/10 P kg + 2.5 t FYM ha-1, which was 49% higher over unfertilized flatbeds. In addition, plant height recorded with 46 N/10 P kg + 2.5 t FYM ha-1 at Errer was higher than with the same amendment at Babile. Main effects of soil moisture and nutrient management significantly affected leaf area indices. Tied ridges had increased leaf area indices by 32% and 28% over flatbeds at Babile and Errer locations, respectively. The highest panicle weight (58% higher over flatbeds) was recorded from Errer for tied-ridges. Likewise, the application of tied ridges with 46 N/10 P kg + 2.5 t FYM ha-1 had increased the panicle weight by 125% over unfertilized flatbeds. At both locations, the main and interaction effects of in-situ moisture conservation and nutrient management on grain and dry biomass yields were significant (P < 0.05). Combining tied ridges with 46 N/10 P kg + 2.5 t FYM ha-1 amendment had increased the grain yield at Babile and Errer by 122 and 128%, respectively, while the dry biomass yield at Babile and Errer locations was increased by 118 and 102%, respectively. The highest stover yield (8967.12 kg ha-1) and harvest index (0.44) were from Errer and Babile respectively with the combined application of tied ridges and 46 N/10 P kg + 2.5 t FYM ha-1. The results also revealed that both the main effects and interaction effect of soil moisture conservation and nutrient management were significant on soil water content, grain and dry biomass water-use efficiencies (WUE), and nitrogen uptake of sorghum. Soil water content at different recording period and soil depth were highest for tied ridges amended with 23 N/5 P kg + 5 t FYM ha-1 followed by tied ridges amended with 5 t FYM ha-1 at both locations. At Babile site, compared to unfertilized flatbeds, the application of tied ridges with 46 N/10 P kg + 2.5 t FY M ha-1 increased the grain-WUE by 110% and the dry biomass-WUE by 99%, whereas, this treatment at Errer increased the grain-WUE by 124% and the dry biomass-WUE by 114%. At both locations, the highest nitrogen uptake in grain and leaf of sorghum were recorded for the combined application of tied ridge and 46 N/10 P kg + 2.5 t FYM ha-1. Moreover, this treatment combination gave the highest net benefit (32,302 Birr ha-1). In conclusion, the results showed that priming sorghum seeds with Zn followed by N solution for the duration of 10 h improved germination and seedling vigor, where varieties Melkam, xix Teshale, and Dekeba have shown better performance with these traits than other sorghum varieties. The on-farm seed priming results also confirmed that Zn or N priming improve stand establishment, growth, and yield of sorghum under prevailing moisture stress in eastern Ethiopia. Furthermore, the results of in-situ soil moisture and nutrient management study demonstrated that combining tied ridges with the application of 46 N/10 P kg + 2.5 t FYM ha-1 could be effective in improving plant growth, yield, water use efficiency and N uptake of sorghum under prevailing condition of semi-arid eastern Ethiopia. Overall, the use of climate-smart technologies such as seed priming, in-situ moisture conservation and integrated nutrient management are beneficial to improve sorghum productivity and increase the resilience of crop production systems against climate risk that predicted to increase in frequency and severity.