Nutrient recycling of selected tree leaf litters in homesteads
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Date
2019
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Department of Agronomy, College of Agriculture, Vellayani
Abstract
The study entitled “Nutrient recycling of selected tree leaf litters in homesteads” was undertaken at College of Agriculture, Vellayani during 2017 to 2019. The main objectives were to identify a suitable method for recycling leaf litters of cashew (Anacardium occidentale L.) and mango (Mangifera indica L.), to assess the effect of the litter composts on growth and yield of vegetable cowpea and to work out the economics of cultivation. The study was conducted as three experiments - i) composting of leaf litter, ii) nutrient enrichment studies and iii) field evaluation of litter compost. The experiment on composting of leaf litter was laid out in completely randomised design with two factors (tree species and composting methods) and three replications during March to November 2018. The treatments were tree species (s1- cashew and s2- mango) and composting methods [c1: co- composting with poultry manure @ 10% w/w, c2: pre-treatment with CI @ 20 g kg-1 followed by release of EW @ 1000 nos m-3 after two weeks, c3: co- composting with glyricidia leaves in 1:1 ratio followed by release of EW @ 1000 nos m-3 after two weeks and c4: natural decomposition (control)]. Leaf litters of cashew and mango were collected during March 2018 and composted as per treatments in cement rings of 120 cm diameter and 50 cm height. Composting was inferred as complete when 95 per cent of the litter was converted to a fine powder with C: N ratio of less than 25: 1. Chemical analysis of leaf litters showed comparatively higher nutrient content and lower C: N ratio in mango. The results of the decomposition study revealed that mango leaf litter decomposed rapidly (154 days) compared to cashew litter (189 days). Among the composting methods, use of CI or glyricidia leaves, both followed by the release of EW (c2) were found to be superior (127 and 156 days respectively). Considering interaction, composting was rapid in mango litter with CI + EW (110 days). Recovery percentage and nutrient content were significantly higher in litters co-composted with glyricidia + EW. The pH, C: N ratio and lignin content varied significantly with species and method of composting. The interaction effect was significant for the fungal count alone. Enrichment with rock phosphate @ 150 g kg-1 and PGPR Mix I @ 10 g kg-1 improved the nutrient content and lowered C:N ratio of the final composts. The pH and microbial count of the enriched composts were higher than that in composted litter. Significant variations among the composts were recorded for N, pH, fungal and actinomycete count. The field evaluation of the litter compost was carried out during December 2018 to March 2019 in randomised block design with 10 treatments replicated thrice in vegetable cowpea (var. Bhagyalakshmy). The treatments T1 to T8 included enriched composts as nutrient sources at 50 per cent substitution of recommended dose of N (KAU, 2016), T9 - control [recommended dose of NPK through chemical fertilizers (KAU, 2016)] and T10 - absolute control (no fertilizers). The remaining dose of N in T1 to T8 and full doses of P and K were given through chemical fertilizers. Results revealed the significant influence of litter composts on growth and yield attributes of cowpea. Plants were taller and recorded higher LAI with application of mango litter composted with glyricidia and EW (T7). Number of pods per plant was the highest for the treatment T5 (33.96) and was on par with T1 (33.4) and T7 (31.88). Pod yield per plant and pod yield ha-1 were found to be significantly higher in T7 (126.61g and 7.8 t) and were on par with T1, T5, T6 and T9. The yield was 9.85 per cent higher than that in KAU POP recommendation (T9). Harvest index was the highest with T7 (0.35) and was comparable with all the treatments except T4, T8 and T10. The highest uptake of N, P and K was recorded with T8, T5 and T6 respectively. Agronomic indices were found to be significantly influenced by the treatments except apparent recovery efficiency for N. Agronomic efficiency and partial factor productivity for N, P and K were the highest with T7, whereas physiological efficiency varied with the nutrient. It was maximum in T1 for N, T7 for P and T5 for K. Available P and K status of soil after the experiment were significantly higher in the treatment which received enriched mango litter composted with glyricidia and EW (T7). The soil P status in T7 was comparable with T8, T6 and T2 and K status, with T1 and T2. Soil microbial count recorded higher values in T7 for bacteria (57.33 x 106 cfu g-1 soil) on par with T6 and T1. Fungal count (22.66 x 104 cfu g-1soil) was significantly higher with T5 on par with T6 and T1 and actinomycete count (33 x 104 cfu g-1 soil) was maximum with T1 and comparable with T5, T7 and T6. Net income (₹ 84003 ha-1) and benefit cost ratio (1.56) were higher in cowpea fertilized with mango litter compost (glyricidia + EW) at 50 per cent substitution of recommended N dose (T7). The results of the study revealed that composting using CI @ 20 g kg-1 or glyricidia leaves in 1:1 ratio, both followed by release of EW @ 1000 nos m-3 after two weeks were the suitable methods for recycling leaf litters of cashew and mango. Substituting 50 per cent recommended dose of N with mango leaf litter composted with glyricidia leaves + EW and enriched with PGPR Mix I and rock phosphate resulted in higher yield, net income and benefit cost ratio in vegetable cowpea.
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