Bio-polymer composite coated urea for yield optimization in amaranth(Amaranthus spp.) for Northern coastal plains of Kerala

Abstract

The investigation on "Bio-polymer composite coated urea for yield optimization in amaranth (Amaranthus spp.) for northern coastal plains of Kerala" was undertaken with an objective to evaluate the efficacy of bio-polymer composites on the release and leaching of N from urea and their effect on the productivity of amaranth in northern coastal plains (AEU 2) of Kerala. The experiment was carried out in five phases as detailed below. Formulation of biopolymer urea composites (BUC) in pellet form using coconut shell charcoal (C1), gypsum (C₂), rice husk biochar (C3), and zeolite (C4) as coating materials and potato starch (S1) and tapioca starch (S2) as binding materials. Coating and binding materials at different ratios (25, 50 and 75% w/w) were examined and standardized for consistency. The optimal ratio (75:25) for each mixture was utilized for coating the prilled urea in 1:1 ratio. Castor oil was uniformly sprayed on the composites after formulation. The urea composites revealed no significant variations in total nitrogen content across different treatments involving coating materials, binding agents, or their combined effects. However, the increase in pH was significant for the treatment C4 The water release studies (T1: Urea, T2 BUC 1 (C1S1), T3: BUC 2 (C1S2), T4: BUC 3 (C2S1), T5: BUC 4 (C2S2), T6 BUC 5 (C3S1), T7: BUC 6 (C3S2), T8, BUC 7 (C4S1) and T9: BUC 8 (C4S2)) revealed marked differences among treatments. Urea exhibited significantly elevated nitrogen release on day one compared to BUC treatments, whereas T9 and T4 initially showed substantially lower values, which gradually increased, reaching significantly higher levels by day 30. The soil incubation study (T1: Urea, T2 BUC 1(C1S1), T3: BUC 2 (C1S2), T4: BUC 3 (C2S1), T5: BUC 4 (C2S2), T6 BUC 5 (C3S1), T7: BUC 6 (C3S2), T8, BUC 7 (C4S1) ,T9: BUC 8 (C4S2) and T10: Control) demonstrated that urea exhibited significantly higher values of ammoniacal nitrogen release on the 7 day, reaching a maximum at 14 days and then decreased gradually till 30 days. All other BUC treatments showed significantly lower release of ammonia into the soil, followed by a gradual increase, reaching a maximum at 90 days. Nitrate nitrogen also exhibited a similar trend. In the soil column study (T1: Urea, T2 BUC 1 (C1S1), T3: BUC 2 (C1S2), T4: BUC 3 (C2S1), T5: BUC 4 (C2S2), T6 BUC 5 (C3S1), T7: BUC 6 (C3S2), T8, BUC 7 (C4S1), T9: BUC 8 (C4S2) and T10: Control) ammoniacal N leaching and nitrate N leaching were maximum in the urea treatment on day 8. The BUC treatments showed significantly lower values. T9 exhibited significantly lower nitrate nitrogen leaching values towards the end of the experiment. Among all treatments, T9 showed initial release of nutrients at significantly lower rates. Furthermore, it had a significantly higher pH compared to other treatments, rendering it suitable for acidic soil. Consequently, T9 (zeolite and tapioca starch) was selected for the field experiment. The field experiment was laid out in factorial randomized block design with two factors replicated thrice. The first factor was nitrogen fertilizer schedule (N1: 100 kg N - 50 kg basal, 50 kg in 2 splits; N₂: BUC 100 kg N basal; N3: BUC 100 kg N 50 kg basal, 50 kg topdressing; N4: BUC 80 kg N - basal; N5: BUC 80 kg N - 40 kg basal, 40 kg topdressing) and the second factor was foliar application (f) after each harvest (F1: Urea 1% (POP); F2: Urea 0.5%; F3: Control).The nitrogen fertilizer schedule treatments exhibited significant differences in growth and yield parameters, with N2 showing maximum values at first harvest and N2 and N3 showing on par values at second harvest. Recovery efficiency of N2 and N4 demonstrated significantly higher values; for agronomic efficiency, N2 and N3 exhibited significantly higher values. The treatments N2 and N3 demonstrated significantly higher values for gross income, net income, and benefit-cost ratio. The findings of the experiment show that applying 100 kg of N as basal through urea coated with zeolite and tapioca starch increased the crop yield at the first harvest. The same fertilizer material and dose applied in two splits (50 kg as a basal and 50 kg as top dressing one month after sowing) increased the yield at the final harvest. Amaranth crop that received 80 kg N as a single dose of BUC produced a yield equivalent to the crop that received 100 kg N in three splits of urea as per KAU POP recommendations. On closer inspection, it becomes clear that amaranth cultivated for a single harvest benefits most from a basal application of 100 kg N through BUC, while amaranth grown for multiple cuts benefits most from two splits of 100 kg N through BUC.