Plant growth regulators are chemical substances which govern all the factors of development and growth within plants. The application of plant growth regulators to crops modifies hormonal balance and growth leading to increased yield, enhanced crop tolerance against abiotic stress and improved physiological trait of crops. Paclobutrazol (PBZ) [(2RS, 3RS)-1-(4-chlorophenyl)- 4, 4-dimethyl-2-(1H-1, 2, 4-trizol-1-yl)-pentan-3-ol], is one of the members of triazole family having growth regulating property. The growth regulating properties of PBZ are mediated by changes in the levels of important plant hormones including the gibberellins (GAs), abscisic acid (ABA) and cytokinins (CK). PBZ affects the isoprenoid pathway, and alters the levels of plant hormones by inhibiting gibberellin synthesis and increasing cytokinins level and consequent reduction in stem elongation. When gibberellins synthesis is inhibited, more precursors in the terpenoid pathway accumulate and that resulted in the production of abscisic acid. PBZ is more effective when applied to the growing media and application on the growing medium would give longer absorption time and more absorption of active ingredient than foliar spray. The application of PBZ to crops is important in reducing plant height to prevent lodging and in increasing number and weight of fruits per tree, in improving the fruit quality in terms of increases in carbohydrates, TSS, TSS/TA and decreases acidity. It further reduces evapo-transpiration and decreases plant moisture stress by enhancing the relative water content of leaf area and develops resistance in the plants against biotic and abiotic stresses. In addition, it acts as highly active systemic fungicide and used against several economically important fungal diseases. In this review, the current knowledge and possible applications of PBZ, which can be used to improve the growth, yield and quality of crops, have been reviewed and discussed. The role of PBZ to mitigate the harmful effects of environmental stresses in crops is also examined. Moreover, various biochemical and physiological processes leading to improved crop production under the effect of PBZ are discoursed in detail.

Mulches are materials applied in a soil surface for different roles and purposes. Plastic mulches with different colour have been developed and utilized in different crop production systems. Using coloured plastic mulches is mainly focused in modifying the radiation budget and decreasing the soil water loss. Besides, it helps to regulate soil temperature, water use efficiency, plant growth, yield, quality and weed and insect infestation. In this review, the knowledge and possible application of coloured plastic mulches, which can improve the soil physical properties, growth, yield, and quality crops has been reviewed and discussed. The role of coloured plastic mulches to mitigate the harmful effect of environmental stress in crops is also examined. Various physicochemical processes leading to improved crop production under the effect of coloured plastic mulches are also discussed. The combined results indicated that, effect of coloured plastic mulches is highly significant on soil temperature, moisture and water holding capacity. While black and blue plastics increase soil temperature, clear and white decreases it. Higher number of fruits, number of roots, tubers and bulbs was recorded in use of coloured plastic mulches. Similarly, the TSS, Vitamin C and juice percentage of different plants also showed significant improvement. It is also reported that weed infestation and viral diseases is highly reduced. Coloured plastic mulches also have some negative impacts like, decrease growth and yield in some plants, increase pest infestation, microplastics contamination, soil puddling, soil structural loss and reduce activity of soil-microorganisms. Therefore, use of coloured plastic mulches require close inspection of interaction with factors like; cropping season, root zone temperature, crop type, insect pest infestation and water use efficiency factors.

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Garlic is an important cash crop in many regions of Ethiopia. However, the yield of the crop is constrained by several factors. Among these, inappropriate clove size is one of the major agronomic practices that can decrease the yield of the crop. Hence, a field experiment was conducted during the 2020/21 main cropping season at Debre Berhan University, College of Agriculture and Natural Resource Sciences, demonstration and research site to evaluate the effect of clove size on growth and bulb yield of garlic (Allium sativum L.). The treatments consisted of five clove sizes: 1–1.49 g, 1.5–1.99 g, 2–2.50 g, 2.51–2.99 g, and 3–3.5 g. An improved variety “Tseday” was used as a planting material. The experiment was laid out as a randomized complete block design in a factorial arrangement and replicated for three times. The results revealed that clove size significantly influenced all growth and yield parameters of garlic. Planting of 3–3.5 g cloves reduced days to emergence by 11 and 6.33 days and days to maturity by 28.33 and 18.00 days, respectively, as compared to planting of 1–1.49 g and 2–2.5 g cloves. This treatment also increased total bulb yield by 25.88% and 15.58%, respectively, as compared to planting of 1–1.49 g and 2–2.5 g cloves. In addition, this treatment significantly increased most of the growth and bulb yield components. Hence, it can be concluded that planting of 3–3.5 g cloves could be recommended to enhance early emergence, good vegetative growth, and total bulb yield of garlic.

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Inappropriate spacing is one of the major problems in tomato production at the study area. A field experiment was conducted to determine inter- and intrarow plant spacing for yield and yield components of tomato at Shewarobit, central rift valley of Ethiopia, under irrigation condition. The treatment comprises of three intrarow spacing (20, 30, and 40 cm) and four interrow spacing (60, 80, 100, and 120 cm) replicated three times and arranged in randomized complete block design using tomato variety Weyno. Data collected on fruit yield and yield components were analysed using SAS. The main effect of interrow spacing significantly affected marketable fruit, unmarketable fruit, marketable fruit number, unmarketable fruit number, and fruit diameter. The 20 cm interrow spacing showed a marked increase in marketable fruit yield by 35.96% as compared to 30 cm spacing used by farmers. Planting tomato in closer interrow spacing (60 cm) resulted in 50% yield increment than the widest (120 cm) space between rows. Interaction effects of both inter- and intrarow spacing significantly (p < 0.05) affected plant height and fruit length. An intrarow and interrow spacing of 20 ∗ 100 cm and 20 ∗ 120 cm resulted in tallest plants and widest fruits, respectively. Therefore, farmers can use 20 cm intrarow spacing and 60 cm interrow spacing for planting of tomato seedling of Weyno variety.

Proper nutrition is one of the factors which is limiting onion production. Onion yield and quality is affected by fertilization of macro and micro nutrients. Mineral nutrients, Nitrogen, phosphorous and Potassium are macronutrients which significantly affect onion production. Nitrogen and phosphorous fertilization significantly affect growth, yield and quality of onion. The requirement of mineral fertilizer varies from place to place, depending on different factors in the growing areas. Effective use of N, P and K fertilizer depends on soil condition, irrigation system, climatic factors and management factors. In all different research reports, it is described that onion is a heavy feeder for N, P, K and the application of these mineral elements enhance production significantly. The quality of onion, physiology and production is highly limited by fertilization of N, P and K fertilizers. Therefore, in this review the effect of mineral nutrition on growth, physiology and yield of onion are discussed and examined in detail.

Keeping in view of lack of recommended rates of N and NPS fertilizers, a field experiment was conducted to evaluate the effect of the newly introduced NPS fertilizer and nitrogen on growth, physiology and above ground biomass of garlic. Four NPS (0-0-0, 78.75-69-12.75, 105-92-17 and 131.25-115-21.25 kg N-P-S ha-1) and three nitrogen fertilizer rates (114.13, 228.26 and 278.33 kg N ha-1) were laid out in Randomized Complete Block Design with three replications. Significantly highest plant height (28.02 cm), leaf diameter (1.27 cm), dry and fresh weight (4.71 g and 6.11 g) and leaf length were recorded on garlic plants supplied with 105-92-17 kg N-P-S ha-1 and also the highest plant height (27.75 cm), leaf length (24.02 cm), fresh and dry weight (6.23 g and 5.04 g) were recorded on garlic plants supplied with 278.33 kg N ha-1. The interaction effect also show a significant effect in almost all the growth parameters; the early day to 50% emergence was recorded from a plot which received 228.26 kg N ha-1 and 105-92-17 kg NPS ha-1 and the highest plant height, leaf length, fresh and dry above ground biomass and leaf diameter were 29.62 cm, 25.60 cm, 6.93 g, 5.59 g and 1.4 cm, respectively were observed by the interaction of 278.33 kg N ha-1 and 105-92-17 kg N-P-S ha-1 with no significant difference with 228.26 N and 78.75-69-12.75 kg N-P-S ha−1. From this one season experiment, fertilizer rates 307.01-69-12.75 kg N-P-S ha−1 could be recommended for garlic production.