Agronomic effectiveness of rice husk and coconut shell biochar -based fertilizers in aerobic rice (Oryza Sativa L.)

Abstract

The present study entitled “Agronomic effectiveness of rice husk and coconut shell biochar-based fertilizers in aerobic rice (Oryza sativa L.)” was undertaken at the Department of Agronomy, College of Agriculture, Vellayani during 2021-2023. The objectives of the study were to assess the nutrient release pattern of rice husk and coconut shell biochar-based fertilizers and to evaluate its effects on growth, yield and nutrient use efficiency of aerobic rice. The study was undertaken in three parts. The first part of the study was conducted at the Department of Agronomy, College of Agriculture, Vellayani during October 2022 to March 2023. Rice husk biochar based fertilizer (BCF 1) was prepared by mixing rice husk biochar (40 per cent), vermicompost (17 per cent), urea (17 per cent), NPK (12-32-16) mix (16 per cent), MOP (3 per cent), ayar (1 per cent), bentonite clay (2 per cent) and humic acid (4 per cent) and coconut shell biochar-based fertilizer (BCF 2) was prepared by mixing coconut shell biochar (40 per cent), vermicompost (18 per cent), urea (16 per cent), NPK (12 32-16) mix (16 per cent), MOP (3 per cent), ayar (1 per cent), bentonite clay (2 per cent) and humic acid (4 per cent) on percentage weight basis followed by pelletization. The initial N, P, and K content of BCF varied from 8.63 per cent to 8.82 per cent, 4.49 per cent to 4.51 per cent and 4.60 per cent to 4.72 per cent, respectively. The storage studies revealed that the N, P and K content of BCF was reduced by 6.83 per cent to 8.04 per cent, 0.89 per cent to 1.33 per cent and 0.65 per cent to 1.05 per cent, respectively at six months after storage. Pelleted BCF retained its shape and no fungal growth was observed during six months of storage. In second part, incubation studies were conducted at the Department of Agronomy, College of Agriculture, Vellayani during October 2022 to January 2023 to study the nutrient release pattern of BCF. The experiment was laid out in completely randomized design with four treatments and four replications. The treatments were T1: 100 per cent recommended dose of nutrients (RDN) as BCF 1, T2: 100 per cent RDN as BCF 2, T3: 100 per cent RDN as KAU POP, T4: Control (No application). BCF 1 and BCF 2 were applied on N equivalent basis for supplying recommended dose of 70:35:35 kg NPK ha-1 for aerobic rice. The results of the study showed that conventional fertilizer treatment (T3) exhibited significantly higher nutrient release, with 96.99 per cent of applied nitrogen, 98 per cent of phosphorus, and 92.65 per cent of potassium released at 20 days after incubation, in contrast to the biochar-based fertilizer treatments (T1 and T2) which showed slower release rates, ranging from 58.27-58.39 per cent for nitrogen, 67.92-69.81 per cent for phosphorus, and 44.99-45.19 per cent for potassium. At 40 DAI, 60 DAI, 80 DAI and 100 DAI, the NPK release rate was higher in biochar-based fertilizers compared to conventional fertilizers. The crop response study (part III) was conducted at farmer’s field located at Kakkamoola, Thiruvananthapuram during January 2023 to May 2023 to evaluate the effect of BCF on growth, yield and nutrient use efficiency of aerobic rice. The experiment was laid out in randomized block design with eight treatments and three replications with the rice variety Prathyasa. The treatments were T1: 100 per cent RDN as BCF 1 (basal); T2: 100 per cent RDN as BCF 2 (basal); T3: 75 per cent RDN as BCF 1 (basal); T4: 75 per cent RDN as BCF 2 (basal); T5: 50 per cent RDN as BCF 1 (basal); T6: 50 per cent RDN as BCF 2 (basal); T7: 100 per cent RDN as KAU POP; T8: control (no fertilizers). BCFs were applied on N equivalent basis for supplying recommended dose of 70:35:35 kg NPK ha-1 for aerobic rice. Basal dose of FYM @ 5 t ha-1 was applied to all plots except T8. Lime was applied to T7 @ 600 kg ha-1. Basal application of 100 per cent RDN as BCF 1 (T1) resulted in taller plants at active tillering (62.01 cm) and panicle initiation stages (89.70 cm) and were comparable with T2. The treatment, T1 also recorded significantly taller plants at flowering (108.72 cm) and harvest stages (109.34 cm). The highest number of tillers per square metre, leaf area and leaf area index were observed in T1 at active tillering (753.33, 691.63 cm2, 4.61 respectively), panicle initiation (763.33, 1014.50 cm2, 6.76 respectively) and flowering stages (710.66, 1179.27 cm2, 7.86 respectively) followed by T2. The treatment, T1 also resulted in higher flag leaf area per hill (143.62 cm2) and dry matter production (10311 kg ha-1) and was comparable with T2. All the growth attributes recorded in T3, T4 and T7 were statistically comparable. The number of productive tillers per square metre was higher in T1 (545.33) and was comparable with T2. The treatment, T1 produced longer panicle (24.38 cm), more number of grains per panicle (161.27), higher panicle weight (3.48 g), grain yield (5859 kg ha-1), straw yield (7083 kg ha-1) and harvest index (0.453) and was statistically similar to T2, T3, T4 and T7. Basal application of 100 per cent RDN as BCF 1 (T1) resulted in higher total chlorophyll content at active tillering (1.89 mg g-1 of fresh weight) and flowering stages (2.11 mg g-1 of fresh weight) and was comparable with T2. The treatment, T1 showed higher nitrogen uptake (153.59 kg ha-1) and was comparable with T2 and T3. The phosphorus uptake was higher in T1 (26.92 kg ha-1) and was comparable with T2. The treatment, T2 exhibited higher potassium uptake (130.23 kg ha-1) and was on par with T1. Basal application of 75 per cent RDN as BCF 1 (T3) showed higher agronomic efficiency and partial factor productivity for N (58.41 kg kg-1, 105.68 kg kg-1 respectively), P (116.81 kg kg-1, 211.37 kg kg-1 respectively) and K (116.81 kg kg-1, 211.37 kg kg-1 respectively) and was comparable with T4. The treatment, T7 showed higher physiological efficiency for N (40.45 kg kg-1) and was comparable with T1, T2, T3 and T4. The physiological efficiency of P (231.07 kg kg-1) and K (49.35 kg kg-1) were higher in T3 and were on par with T1, T2, T4 and T7. The treatment, T3 exhibited higher apparent recovery efficiency for N (1.55 kg kg-1) and was comparable with T1, T2 and T4. The apparent recovery efficiency for P (0.50 kg kg-1) and K (2.36 kg kg-1) was higher in T3 and was comparable with T4. The soil available N was higher in T1 (338.69 kg ha-1) and was on par with T2, T3 and T4. The soil available P was higher in T1 (72.91 kg ha-1) and was on par with T2. The soil available K was higher in T2 (291.24 kg ha-1) and was comparable with T1, T3 and T4. The treatment, T2 exhibited higher dehydrogenase activity at 30 DAS (25.97 g TPF g-1 soil d-1), 50 DAS (23.16 g TPF g-1 soil d-1) and 80 DAS (18.55 g TPF g-1 soil d-1) and was comparable with T1. The highest actual gain of N (75.27 kg ha-1) and P (31.30 kg ha-1) was observed in T1 and the highest actual balance of K was observed in T2 (30.10 kg ha-1). Basal application of 100 per cent RDN as BCF 1 (T1) resulted in higher gross income (₹ 192394 ha-1), net income (₹ 51669 ha-1) and BC ratio (1.37) and was statistically comparable with T2, T3 and T4. Thus from the study, it could be concluded that conventional fertilizers demonstrated higher nutrient release, releasing 96.99 per cent of applied nitrogen, 98 per cent of phosphorus, and 92.65 per cent of potassium at 20 days after incubation, while biochar-based fertilizer treatments displayed slower release rates, ranging from 58.27-58.39 per cent for nitrogen, 67.92-69.81 per cent for phosphorus, and 44.99-45.19 per cent for potassium. Basal application of 100 per cent and 75 per cent RDN as BCF resulted in comparable yield and profit. Thus, basal application of FYM @ 5 t ha-1 + either rice husk or coconut shell BCF @ 600 kg ha-1 (equivalent to 75 per cent recommended dose of NPK of aerobic rice (i.e. 52.5: 26.25: 26.25 kg NPK ha-1) could be recommended as the productive, profitable and more efficient nutrient schedule for cultivating aerobic rice.