Evaluating the effect of green manuring and zinc fertilization on yield, economics and post- harvest nutrient status of transplanted rice (Oryza sativa L.)

Introduction

Rice (Oryza sativa L.) is a staple food for over half the world's population, particularly in Asia, where 90 per cent of global production and cultivation occur. Its widespread cultivation and consumption have earned it the title "global grain". India, the world second-largest rice producer after China, faces significant challenges in meeting the increasing demand for rice while addressing environmental concerns. In India, 47.83 million hectares are used for rice cultivation, with a production of 135.75 million tonnes of grain annually and 2.8 t ha -1 of productivity (MAFW, 2023) [6] . The declining quality and quantity of rice production, coupled with rising environmental issues, necessitates innovative and sustainable agricultural practices. Green manuring, a method of incorporating organic matter into the soil through plant residues, emerges as a promising solution. By enhancing soil fertility, organic carbon content, and nutrient availability, green manuring promotes healthier crop growth and increased yields (Valizadeh et al., 2023) [15] . The most critical concern in rice production is meeting the ever-increasing global demand for rice, particularly without compromising nutritional quality. As the world population continues to grow, so too does the need for this essential staple food. Ensuring that rice production can keep pace with this demand while maintaining its nutritional value is a paramount challenge for agriculture and food security. Zinc deficiency is a major constraint to rice grain yield and a global nutrition concern. As a vital micronutrient involved in various plant physiological processes, zinc plays a crucial role in increasing production, improving plant defense and activating antioxidant enzymes. Combining green manuring with zinc fertilization offers a synergistic approach to sustainable rice production.

This approach not only increases yields and improves nutritional quality but also reduces the environmental impact of agriculture by minimizing the need for synthetic fertilizers and soil degradation (Baral et al., 2024) [3] Integrating NPK (nitrogen, phosphorus, potassium) fertilizers, green manures, zinc fertilizers, solubilizers and nano zinc in rice cultivation represents a multifaceted strategy to enhance soil fertility, improve crop yield, and ensure nutrient efficiency. By combining these elements, rice cultivation can achieve a more balanced nutrient profile, improved soil health and greater resilience against nutrient deficiencies, leading to increased productivity and sustainability.

Materials and methods

A field study was carried out during June 2023 -September 2023 at the Experimental Farm, Department of Agronomy, Faculty of Agriculture, Annamalai University, Annamalai Nagar, Cuddalore District, Tamil Nadu. The experimental farm is situated at 11º 24' N latitude and 79º 44' E longitude and an elevation of + 5.79 m above Mean Sea Level (MSL). The experimental was laid out in RBD with eight treatment and replicated thrice. The treatments are T 1 -Control; T 2 -RDF (120:40:40 kg N P 2 O 5 K 2 O ha -1 ); T 3 -RDF + GM @ 6.25 t ha -1 + Soil application of ZnSO 4 @ 25 kg ha -1 ; T 4 -RDF + GM @ 6.25 t ha -1 + Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage; T 5 -RDF + GM @ 6.25 t ha -1 + Soil application of 1.0 L ha -1 Zn solubilizers; T 6 -RDF + GM @ 6.25 t ha -1 + Soil application of ZnSO 4 @ 25 kg ha -1 + Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage; T 7 -RDF + GM @ 6.25 t ha -1 + Soil application of ZnSO 4 @ 25 kg ha -1 + Soil application of 1.0 L ha -1 Zn solubilizers and T 8 -RDF + GM @ 6.25 t ha -1 + Soil application of ZnSO 4 @ 25 kg ha -1 + Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage + Soil application of 1.0 L ha -1 Zn solubilizers. Rice variety ADT 43 was selected for the study with a seed rate of 60 kg ha -1 . The green manure applied was Sesbania aculeata @ 6.25 t ha -1 . The data for yield viz., grain and straw yield and economics were computed. And also the post-harvest nutrient status were also analyzed. Standard agronomic practices were adopted. The harvested mature crop from the net plot area was subjected to manual threshing, winnowing, and thorough sun drying. The dried grains were weighed, their moisture content was determined to be 14%, and the yield was calculated and expressed in kilograms per hectare (kg ha -1 ). Additionally, the weight of the dried straw was measured and recorded in kg ha -1 . Post-harvest soil samples were collected randomly from the experimental fields to a depth of 15 cm and then pooled together. To assess the available nutrient content, composite soil samples were dried, ground into a fine powder, and sieved through a 2 mm mesh. The various growth and yield parameters observed during the study were analyzed statistically using the methods outlined by Gomez and Gomez (1984) [5] . Significant differences between treatments were determined using the 'F' test at a 5% probability level (P=0.05), and the critical difference (CD) was calculated accordingly. Non-significant treatment differences were indicated by 'NS'.

Table 1: Effect of green manuring and zinc fertilization on yield of transplanted rice

Treatments

Straw yield (kg ha -1 ) T1-Control 1500 3250 T2-RDF only 3645 6797 T3 -T2 + GM @ 6.25 t ha -1 + Soil application of ZnSO4 @ 25 kg ha -1 4409 7493 T4 -T2 + GM @ 6.25 t ha -1 + Foliar application of 0.2% Nano Zn at 50% flowering, Milky and dough stage 4621 7835 T5 -T2 + GM @ 6.25 t ha -1 + Soil application of 1.0 L ha -1 Zn solubilizer 4184 7145 T6 -T2 + GM @ 6.25 t ha -1 +Soil application of ZnSO4 @ 25 kg ha -1 + Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage 5355 8560 T7 -T2+ GM @ 6.25 t ha -1 + Soil application of ZnSO4 @ 25 kg ha -1 + Soil application of 1.0 L ha -1 Zn solubilizer 4878 8194 T8 -T2+ GM @ 6.25 t ha -1 + Soil application of ZnSO4 @ 25 kg ha -1 + Soil application of 1.0 L ha

Results and Discussion Yield

The data revealed that the application of RDF,GM @ 6.25 t ha - 1 ,Soil application of ZnSO 4 @ 25 kg ha -1 , Soil application of 1.0 L ha -1 Zn solubilizer and Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage (T 8 ) was the most effective treatment. This treatment resulted in the highest grain yield (5726 kg ha -1 ) and straw yield (8960 kg ha -1 ) at harvest (Table 1). This increase is primarily attributed to the enhanced nitrogen availability from green manure incorporation, which improves soil structure and microbial activity. Rice yield is directly influenced by nitrogen and phosphorus content, while potassium plays a crucial role in plant stress tolerance (Moe et al., 2019) [7] . Green manure incorporation provides a sustained release of biologically fixed nitrogen, improving nutrient availability and crop growth. It also enhances plant growth and dry matter accumulation, leading to higher straw yield compared to the control treatment. These findings were similar with those findings of Sravan et al. (2016) [12] and Winarni et al. (2016) [16] . Crop yield is determined by the interplay between photosynthetic capacity and grain development, with efficient photosynthate translocation and partitioning being crucial. Zinc involvement in enzyme systems, regulatory functions, and its role in auxin synthesis, carbohydrate production, and transport to grain-filling sites are crucial for enhancing crop yield. Zinc plays a pivotal role in enhancing crop yield by acting as a cofactor in numerous enzyme systems, regulating physiological processes, and boosting carbohydrate synthesis and translocation to grain-filling sites (Shukla et al., 2022) [11] . Zinc is a key micronutrient that significantly enhances rice yield through a complex interplay of physiological processes. By catalyzing the interconversion of CO 2 and HCO 3-through carbonic anhydrase, zinc accelerates photosynthesis, leading to increased biomass accumulation and grain yield. Furthermore, zinc role in stomatal conductance and anaerobic root respiration is crucial for optimizing water use efficiency and stress tolerance. These physiological enhancements, combined with increased tiller and panicle production, collectively contribute to higher grain yield and improved rice productivity. This findings aligns with those of Rout et al. (2020) [10] ; Akmal et al. (2023) [1] and Ramesh (2024) [9] .

Economics

The study demonstrated a significant disparity in economics of the crop examined across various nutrient management practices (Table 2). Among all treatments, the application of RDF, GM @ 6.25 t ha -1 ,Soil application of ZnSO 4 @ 25 kg ha -1 , Soil application of 1.0 L ha -1 Zn solubilizer, Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage (T 8 ) emerged as the optimal practice. This treatment resulted in the highest gross returns (Rs.144892 ha -1 ), net returns (Rs.75450 ha - 1 ) and BCR (2.00). The improved economic performance of the optimal treatment can be attributed to the enhanced yield resulting from the synchronized release and efficient utilization of nutrients derived from organic and inorganic sources. Additionally, the effective agronomic practices associated with the application of these inputs further boosted grain and straw yield, ultimately reflecting positively on the benefit-cost ratio. Alleviation of zinc deficiency through fertilizer application contributed to increased yield and, consequently, higher net returns (Sucharita et al., 2023) [13] .

Post-harvest nutrient status

Integrated nutrient management significantly influenced postharvest nutrient status (nitrogen, phosphorus, potassium, and zinc). The treatment combining RDF,GM @ 6.25 t ha -1 ,Soil application of ZnSO 4 @ 25 kg ha -1 , Soil application of 1.0 L ha -1 Zn solubilizer, Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage (T 8 ) demonstrated the highest post-harvest nutrient status (Table 3).This treatment resulted in highest post-harvest soil available N (238.2 kg ha -1 ), P (23.4 kg ha -1 ), K (285.5 kg ha -1 ) and Zn (1.55 mg kg of soil -1 ). This is due to the integrated application of inorganic fertilizers, organic manures, and zinc significantly improved soil nutrient content and availability, promoting optimal crop growth and nutrient cycling through root exudates. Organic matter amendments ameliorated soil texture, drainage, and pH, thereby enhancing nutrient solubility and availability. Additionally, the gradual release of micronutrients from organic sources, such as iron, manganese, and copper, reduced nutrient leaching and promoted nutrient retention within the crop soil system. These findings corroborate the research of Devi et al. (2022) [4] and Sutardi et al. ( 2022) [14] . The increased soil zinc concentration observed with Zinc Solubilizing Bacteria (ZSB) application can be attributed to enhanced zinc solubilization and subsequent increased root growth. Nutrient uptake dynamics in rice were intricate, with macro-(N, P, K) and micronutrients (Zn) exhibiting interdependencies. Zinc availability declined progressively throughout the crop cycle due to plant uptake and potential losses. The combined application of ZnSO 4 and zincsolubilizing bacteria mitigated zinc adsorption, thereby increasing its availability. Notably, Bacillus spp., known for their resilience, likely persisted in the rice rhizosphere, contributing to sustained zinc solubilization and increased postharvest soil zinc levels. This finding aligns with the research of Prathap et al. (2022) [8] and Ali et al. (2023) [2] . 1.42 T3 -T2 + GM @ 6.25 t ha -1 + Soil application of ZnSO4 @ 25 kg ha -1 66448 113348 49900 1.70 T4 -T2 + GM @ 6.25 t ha -1 + Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage 67973 118269 53296 1.73 T5 -T2 + GM @ 6.25 t ha -1 + Soil application of 1.0 L ha -1 Zn solubilizer 65567 104307 41740 1.59 T6 -T2 + GM @ 6.25 t ha -1 + Soil application of ZnSO4 @ 25 kg ha -1 + Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage 70648 136046 68398 1.92 T7 -T2 + GM @ 6.25 t ha -1 + Soil application of ZnSO4 @ 25 kg ha -1 + Soil application of 1.0 L ha -1 Zn solubilizer 68242 125117 59875 1.83 T8 -T2 + GM @ 6.25 t ha -1 + Soil application of ZnSO4 @ 25 kg ha -1 + Soil application of 1.0 L ha -1 Zn solubilizer + Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage 72442 144892 75450 2.00 1.04 T3 -T2 + GM @ 6.25 t ha -1 + Soil application of ZnSO4 @ 25 kg ha -1 232.6 19.6 267.2 1.19 T4 -T2 + GM @6.25 t ha -1 + Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage 234.0 20.5 271.1 1.28 T5 -T2 + GM @ 6.25 t ha -1 + Soil application of 1.0 L ha -1 Zn solubilizer 230.7 18.9 263.7 1.12 T6 -T2 + GM @ 6.25 t ha -1 + Soil application of ZnSO4 @ 25 kg ha -1 + Foliar application of 0.2% Nano Zn at 50% flowering, milky and dough stage 236.8 22.4 280.6 1.46 T7 -T2 + GM @ 6.25 t ha -1 + Soil application of ZnSO4 @ 25 kg ha -1 + Soil application of 1.0 L ha -1 Zn solubilizer 235.4 21.4 276.0 1.36 T8 -T2 + GM @ 6.25 t ha -1 + Soil application of ZnSO4 @ 25 kg ha -1 + Soil application of 1.0 L ha