Conservation tillage and nano nitrogen nutrition in Chinese potato (Plectranthus rotundifolius (poir.) spreng.)

Abstract

The study entitled "Conservation tillage and nano nitrogen nutrition in Chinese potato [Plectranthus rotundifolius (Poir.) Spreng]" was conducted at College of Agriculture, Vellayani during 2021-2023. The objective of the study was to assess the impact of conservation tillage and nano nitrogen nutrition on the growth, tuber yield and quality in Chinese potato, and carbon build up in the soil. The field experiment was executed during December 2022 to May 2023 at College of Agriculture, Vellayani. The experiment was laid out in split plot design with three methods of tillage [c1: Conventional tillage, c2: Reduced tillage (RT)+ surface incorporation of green manure (GM) cowpea and c3: RT+ surface retention of GM cowpea] as main plot treatments, and four N management practices [n1: 100% recommended dose of nitrogen (RDN) + nano urea, n2: 75% RDN+ nano urea, n3: 50% RDN+ nano urea and n4: 100% recommended dose of fertilizers (RDF)] as sub plot treatments, in three replications. In RT treatments, fodder cowpea variety Aiswarya was raised as green manure crop @ 20 kg seeds ha-1 and incorporated/ surface retained as mulch at flowering stage (45 DAS). Secondary ploughing in c2 and c3 plots was confined to the row zone alone. Cuttings of Chinese potato variety Suphala were planted at a spacing of 30 cm x 15 cm in all the plots. The NPK recommendation followed was 60: 60: 100 kg ha-1 (KAU, 2016). Nano urea (@ 0.4%) was sprayed 20 and 40 days after planting (DAP) as per treatments fixed. Other cultural operations were done in accordance with the KAU package recommendation for the crop. The treatment, c2 resulted in significantly taller plants at 90 and 120 DAP, higher number of branches per plant at 120 DAP and superior leaf area per plant at 30, 60 and 120 DAP. Among the subplot treatments, the significantly taller plants at 30 and 60 DAP, plant spread at 30, 60 and 90 DAP and number of branches at 30 DAP were recorded in n3. The treatment n1 recorded the highest leaf area at all the growth stages. Among the interactions, plants in c2n3 were significantly taller at 30 and 60 DAP, with the highest plant spread and leaf area at all stages of observation. The yield attributes and yield, number of tubers per plant (21.59), average tuber weight (12.13g) and marketable tuber yield (130.67 g per plant) were significantly the highest in c2. Tuber yield (16.20 t ha-1) was significantly higher in c3 and comparable with c2. In N management, n3 (50% RDN + nano urea) resulted in highest number of tubers and yield, and were the lowest in n4. Among the c x n interactions, c2n3 produced the highest tuber yield (17.74 t ha-1). Significantly higher chlorophyll contents were observed in c2 and was on par with c3. The chlorophyll content in n1 and n3 remained similar at 30 DAP and at 60 DAP, n1 was superior. The treatment combination c2n3 recorded the highest chlorophyll content at 60 DAP. Crop growth rate computed until 90 DAP, were significantly higher in c2 and during 90-120 DAP, in c3. It remained the highest in n1 upto 60 DAP and thereafter, n3 and n2 recorded the higher values. Leaf Area Index was higher in c2 but on par with c3. The highest LAI was recorded in c2n1 at all growth stages. No significant variations were found in days to start of senescence and biomass partitioning at the start of senescence due to tillage methods and interactions. Biomass accumulation followed the order tuber > stem > leaf, in all treatments. In tubers, significantly the highest biomass (66.4%) was recorded in n3. Nutrient uptake was higher for N and K in c2 and P uptake, in c3. With respect to N management, significantly higher N uptake was computed in n1 while P and K uptake were the highest in n3. Among interactions c2n3 was superior. Quality of tubers in terms of vitamin C and protein contents remained on par in c3 and c2 and among N management treatments, superior vitamin C content was observed in n3, and protein in n1. Starch content was the highest in n1 on par with n2. Among the treatment combinations, the highest starch and protein contents were observed in c2n1, and vitamin C in c2n3. The methods of tillage, N management and their interaction showed varied effects on soil nutrient status and were more pronounced for P, S and Zn. Conservation tillage methods (c2 and c3) elicited significant variations in soil C status. The highest TOC (11.80 g kg-1) and labile C (4.94 g kg-1) were recorded in c2 while non labile C (7.64 g kg-1) was the highest in c3. The C stock (5093 g m-2) was the highest in c3 and among interactions, c2n3 recorded the highest TOC. Soil microbial population and dehydrogenase activity were the highest in c2 and among c x n interactions, the combinations including c2 was superior. Economic analysis revealed c2n3 as the most profitable treatment combination for Chinese potato cultivation. The net income and BCR computed were ₹429657 ha-1 and 2.54 respectively. Based on the results of the study, in Chinese potato, the practice of raising GM cowpea sown @ 20 kg seeds ha-1, incorporation of biomass at flowering, planting stem cuttings in reduced tilled beds and nutrient management with 30 kg N (50% RDN), 60 kg P2O5, 100 kg K2O ha-1 + nano urea foliar spray (0.4%) at 20 DAP and 40 DAP, can be recommended as the most suitable conservation agriculture strategy. The C stock in soil was found to improve with conservation tillage practices.