Growth and yield response of broccoli to irrigation techniques and different plastic mulch thicknesses on a ferralsol
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Over the past decades, climate change and variability have emerged as one of the leading constraints a major achieving potential production in agriculture especially in Sub-Saharan Africa (SSA). Most farmers in SSA are still dependent on rain-fed agriculture and are unable to cope with unpredictable weather patterns notably uneven rainfall distribution in the growing seasons. To mitigate water stress, efforts like the conservation of soil moisture to provide some moderate water during the dry phases of the year for plant growth are being recognized. For example, plastic mulching and irrigation are being practised among stakeholders in agriculture. This study was carried out to assess the feasibility of using plastic mulch under small-scale irrigation for offseason production of broccoli on a ferralsol. The experiment was carried out at Makerere University Agricultural Research Institute Kabanyolo (MUARIK) from January to March 2022 during the dry season. A three-factorial experiment; co plastic mulch thickness (1000 mm, 500 mm and 0 mm or bare), irrigation techniques (water bottle drip and watering can) and fertilizer levels (optimum and sub-optimum rates) was used. The treatment combinations were laid out in a Randomized Complete Block Design on the upper slope position of the local relief. Broccoli seedlings were transplanted after 30 days from the nursery bed. The mulch treatments were placed at transplanting while irrigation techniques and fertilizer levels were introduced 14 days after transplanting (14 DAT). Broccoli plants initially in the unmulched or bare plots performed better days after transplanting compared to the mulched ones due to strong plant shock from mulch. However, before introducing irrigation treatment plants from the plastic mulched plots latter picked up and out-performed those from the unmulched ones. Initially, under bare plots, on average broccoli plants were taller (33.3 cm), grew more leaves (10) and visually showed more biomass yield than those under unmulched treatment. Irrespective of irrigation technique and fertilizer levels, a 1000 mm gauge mulch had a significantly higher a biomass yield 1224.3±24.4 g m-2, which was a 10.57% increase in yield biomass than 500 mm gauge plastic mulch under optimum fertilizer. Bottle drip irrigation produced higher biomass yields than watering cans under fertilizer and mulch treatments combinations. Irrigation technique had a significant (p < 0.05) effect on broccoli growth under no mulch (bare plots) for example a biomass of 685.9 g m-2 for bottle drip compared to 604.4 g m-2 for watering can. Weed pressure measured as weed dry matter per unit area at each weeding times was generally low and negligible in mulched than bare plots.. For the same fertilizer level, the thickest gauge of mulch and bottle drip irrigation resulted in the highest biomass at harvest of 1224.3 g m-2. This study demonstrated that use of plastic mulch provides; (i) an opportunity to save labour and time for weeding, (ii) accelerates and boots broccoli growth and (iii) enhances fertilizer uptake. These findings have strong implications for broccoli production among smallholder resource constrained farmers.