Growth, Water Relation, Yield and Crop Quality of Arabica Coffee in Response to Water Stress and Deficit Irrigation.

Field: Agricultural and Biological Sciences (Life Sciences)

Coffee (Coffea Arabica L.) is the single most important commodity crop that comes \nafter petroleum in the world market. It plays a significant role in the economy of \nEthiopia, contributing over 60% of the nation's foreign exchange earnings, 30% of the \ngovernment's direct revenue, 8% output of the agricultural sector and 4% of the gross \ndomestic production. In spite of the importance of the crop in the country's economy, its \naverage national yield is very low primarily because of traditional production \ntechnologies. Apart from hereditary characteristics of the trees, seasonal water stress and \nrecurrent drought are among the major factors which account for low yields of the crop \nin most coffee growing regions of the country. In the present study, attempt was made to \nidentie water stress tolerant Arabica coffee cultivars and deficit irrigation practices that \ncould improve growth, yield, quality and water use efficiency of the crop under both \nprotected environment and field condition in Ethiopia. Both rain shelter and field \nexperiments were carried out in a randomized complete block design with three \nreplications in the rain shelter and four replications in the field. In the first rain shelter \n~EWSTAWUN %TAN MJU- SAMAD \nUWEfirn m MAww \nthan NDI for coffee production particularly in areas where water is scarce and dry spells \nare prolonged. On the other hand, the effect of supplemental deficit irrigation on plant \nwater relations, crop yield and quality was studied in the field using young coffee stands \nof three cultivars (F-59, 74110 and 75227). Two irrigation treatments, namely, \nsupplemental full irrigation (SFI) and supplemental deficit irrigation (SDI), applied in \nthe conventional way, were compared against rain fed (RF) control. SF1 consistently \nincreased soil moisture content, leaf RWC and g, during the dry period, but there was no \ndifference between the treatments in the main wet season. Besides, SF1 significantly \nincreased coffee yield, but the difference between SF1 and SDI was not significant and \nyet SDI had 21 - 24% yield advantage over the RF treatment. On the other hand, overall \nquality of coffee beans was considerably increased by SDI and RF treatments. \nTherefore, SDI seems to be more effective than SF1 and it can be used as an option next \nto PRD for coffee production in drier areas. \nstudy, twenty four known cultivars, which are indigenous to the country, were subjected \nto a soil drying treatment to identify those tolerant genotypes. Variations among the \ncultivars for mean stress scores, rate of recovery from drought, root to shoot ratio, \nconcentration of inorganic solutes (K, Ca and Mg) in leaves, specific leaf area and \nsurvival rate showed that some of the genotypes, such as 741 10, 741 12 and 8/85, were \nless sensitive to water stress at seedling stage. On the other hand, in an experiment \nwhere three irrigation regimes (well watering, WW, normal deficit irrigation, NDI, and \npartial root zone drying, PRD) were studied on cultivar F-59 grown in a rain shelter, it \nwas found that NDI and PRD reduced shoot growth, total dry matter production, dry \nweights of leaves, stem and roots, leaf relative water content (RWC) and stomata1 \nconductance (g,), but increased root to shoot ratio and irrigation water use efficiency \n(IWUE) of coffee seedlings. Therefore, it was concluded that PRD is an effective deficit \nirrigation practice to increase I'WUE and decrease irrigation water requirement by 50% \nwithout substantial adverse effects on plant growth and development, and it could be \npractically advantageous in coffee nurseries especially in areas of water scarcity and \nprolonged drought periods. The same study was carried out in the field to determine the \neffect of PRD on plant water relations and crop yield and quality of Arabica coffee. \nResults of the field experiment also indicated that leaf RWC, g,, h i t growth rate and \nsome yield components were reduced by both PRD and NDI. However, the difference \nbetween WW and PRD was not significant for crop yield and yet PRD resulted in over \n41% more IWUE than the WW treatment, reduced the amount of irrigation water by \n50% and considerably improved both raw and liquor quality of coffee beans. Hence, it \nwas concluded that PRD can be a feasible irrigation strategy, which can save irrigation \nwater, increase IWUE and maintain crop yield, and it appears to be more advantageous