Title : Water regimes in selected fodder radish (Raphanus sativus) cultivars: Effect on nutritional value and in vitro dry matter degradability
Abiotic factors such as amount of water received by plants influence the nutrient concentration of most fodder crops. The nutrient concentration of newly bred ARC fodder radish cultivars is not known yet. We predicted that (i) well-watered (W1) would have high CP, CF, Solubility, DMD, chemical estimates and mineral concentration than moderate stress (W2) and severe stress (W3), but (ii) W2 and W3 will result in high TNC, ADF, NDF and ADL than W1. To test these predictions, field experiment was conducted at ARC-VOP, Pretoria, South Africa, during the 2021/2022 winter season. Factors were three irrigation regimes (W1, W2 and W3) and two radish cultivars (Endurance and Line2) replicated thrice. After four month, harvested fresh leaves and tubers were oven-dried at 70 °C for 96 hours then milled for analysis. Two way Anova was used to test measured variables. Both Endurance and Line2 leaves under W2 had the highest (p < 0.05) CP content (185.29 g/kg and 245.70 g/kg) respectively. Endurance tubers under W2 had the highest (p < 0.05) CP content (92.35 g/kg). While Line2 tubers under W1 (88.57 g/kg) had the highest CP content. Endurance leaves under W1 had the higher NDF, CF, TNC and solubility when compared to the same water level in Line2 cultivar. Line2 leaves under W2 had higher ADF, ADL, CF and solubility when compared to the same water regime in Endurance. On tubers, Endurance had the highest CF concentration under W1, ADF and NDF under W3, then ADL and solubility under W2. Line2 leaves under W1 had the highest ADF, NDF and solubility, while the ADL and CF was high under W3. Both cultivars, tubers had higher TNC under W3. While Endurance leaves under W1 at 48h had higher (p < 0.05) in vitro ruminal degradability (7870 g/kg DM). Whereas, Line2 leaves in W1 had higher (p < 0.05) in vitro ruminal degradability in all the incubation period. Again Endurance tubers under W2 resulted in high (p<0.05) IVDMD in all the incubation periods. While Line2 W3 had higher (p < 0.05) in vitro ruminal degradability (820.12 g/kg DM) at 48h. In both cultivars, leaves and tubers water level affected the macro and micronutrients, with the entire measured mineral beside copper meet the cattle and minimum requirements. The water regimes have an influence on the nutritive value of newly ARC bred cultivars, however all the measured variables meet the minimum requirements for livestock. During dormant season, forages/grass drastically decreases in minerals and crude protein. Endurance and Line2 showed high CP, maro minerals and DMD under moderate stress water regime, which was 221 mm total water applied, while well-watered was 305 mm. Implying that Endurance and Line2 can be used as supplement for livestock even under limited water. Data from this study will be able to assist farmers in selecting the best species that adapt well in low water level for the maximum nutrient yields on fodder radish, also help seed companies in marketing of these cultivars. Farmers who use irrigation for forages especially the dairy industry should use Endurance and Line2 for the benefit of high nutritional yield with less water, using 305 mm for fodder radish as the wastewater as South Africa declared as drought country. There is a need for metabolic feeding trials to assess of livestock fed in these cultivars.
Keywords: nutrient yield, water use, irrigation, livestock, forages, brassicas