Agrotechniques for enhancing root production in Desmodium gangeticum (L.) DC under partial shade

Abstract

The study entitled “Agrotechniques for enhancing root production in Desmodium gangeticum (L.) DC. under partial shade” was undertaken during 2017-2019, in the Instructional farm, College of Agriculture, Vellayani, Thiruvananthapuram, Kerala, with an objective to study the integrated effect of root endophyte fungus, planting density, source efficacy of nutrients, moisture stress and subsurface mulching on the growth, yield and quality constituents of Desmodium gangeticum (L.) DC. under partial shade. The field experiment was laid out in randomized block design with 12 treatments and three replications. The treatments were, T1 – Inoculation with Piriformospora indica (root endophyte) alone, T2 – T1 + Soil application of cow dung slurry (5% at monthly interval), T3 – T1 + Soil application of NPK (basal- @ 40:40:40 kg ha-1 year-1), T4 – T2 + Irrigation at 15 mm depth, T5 – T2 + Irrigation at 30 mm depth, T6 – T3 + Irrigation at 15 mm depth, T7 – T3 + Irrigation at 30 mm depth, T8 – T5 at high density planting (40 cm x 20 cm), T9 – T7 at high density planting, T10 – T8 under subsurface mulching with black polythene, T11 – T9 under subsurface mulching with black polythene and T12 – control at normal row planting (40 cm x 40 cm). Piriformospora indica was inoculated with the potting medium @ 10g fungal culture kg-1 of potting medium. Results of the experiment revealed that integrated management practices have significant effects on growth and yield attributes of D. gangeticum. The treatment T7 recorded the tallest plants at 3 and 4 months after transplanting (MAT) whereas, T9 was superior at 5, 6 and 7 MAT and at harvest. The treatment T7 registered the highest number of branches at all stages of growth. At 3 and 5 MAT, T6 recorded the highest leaf number whereas T7 was superior at 4, 6 and 7 MAT and at harvest. T5 registered the highest root number at 3 MAT but T10 was found superior at 5, 6 and 7 MAT and at harvest. At 2 MAT, T9 and at all other growth stages, T7 recorded the highest root spread. T5 at 3 MAT, T7 at 5 and 6 MAT and at harvest and T6 at 7 MAT registered the highest root volume. With respect to length of tap root, the treatments T9 at 3, 4, and 6 MAT and at harvest and T8 at 7 MAT were found superior. At 3 MAT, T5 revealed the highest girth of primary root but at 5, 6 and 7 MAT, T7 and at harvest T6 were found superior. The treatment, T7 registered the longest laterals at 5, 6 and 7 MAT and at harvest. The root fresh and dry weight showed a similar trend. The treatments T9 at 3 MAT, T6 at 5 and 7 MAT and T7 at 6 MAT and at harvest showed the highest fresh and dry root weight. The highest root yield at harvest was recorded by T8 which was on par with T9, T10 and T11. Chlorophyll content varied with different growth stages. T5 at 2 MAT, T6 at 5 MAT, T11 at 6 MAT and T9 at 4 and 7 MAT and at harvest registered the highest total chlorophyll content. Like chlorophyll content, RLWC also showed variations with respect to different growth stages. T2 at 3 and 4 MAT, T6 at 7 MAT and T7 at 5 and 6 MAT and at harvest recorded the highest values. At 5 and 7 MAT and at harvest T7, T5 and T6 respectively recorded the highest root-shoot ratio. The treatments T11 and T9 at 2 and 7 MAT and T8 at 3, 5 and 6 MAT and at harvest registered the highest leaf area index. Observations on crop growth rate showed the significance of T8 at 4 to 5 MAT, T6 at 6 to 7 MAT and T9 at 5 to 6 MAT and 7 MAT to harvest. With respect to relative growth rate, T4 at 2 to 3 MAT and T6 at 3 to 4, 4 to 5 and 6 to 7 MAT followed by T9 at 7 MAT to harvest were found superior. At 2 to 3 and 4 to 5 MAT, the treatments T11 and T10 respectively recorded the highest values for net assimilation rate. Ethanol extract of plant roots grown under control at normal row planting (40 cm x 40 cm) (T12) recorded the highest total alkaloids at harvest. Among seed parameters, only number of seeds per inflorescence was significantly influenced by the treatments at 6 MAT and it was the highest in T1. Soil moisture studies revealed the significance of T8 and T9 in enhancing soil moisture retention before and after irrigation. T4 on par with T6 registered the highest consumptive use, daily consumptive use and Kc. Crop water use efficiency was the highest for the treatment T8. T2 registered the highest field water use efficiency and water productivity. T9 recorded the highest up take of primary plant nutrients. After the experiment, organic carbon and available K status of soil were found superior in T3 and T10. Even though nursery seedlings exhibited P. indica root colonization at harvest, it was not clearly evident through microscopic investigation. Economic analysis of the system revealed the significance of T8 (₹ 47,902 ha-1) which was on par with T9 and T10 with respect to net income. The highest benefit-cost ratio was also registered by T8 which was significantly superior to all other treatments. It is concluded that high density planting of P. indica inoculated seedlings under partial shade followed by monthly application of cow dung slurry (5 %) and scheduling irrigation at 30 mm depth once in six days (T8) was found beneficial for enhancing leaf area index, root production, crop water use efficiency, net income (₹ 47,902 ha-1) and benefit-cost ratio (1.74).