The study titled " Effect of Graded Level of Nutrients on Quality of tree Mulberry and Larval Parameters of Silkworm Bombyx mori L." was conducted during 2022 at Krishi Vignana Kendra, Haradanahalli Farm, Chamarajanagara, to determine the impact of optimal nutrient combination on quality of mulberry. The findings highlighted that the plants treated with 40 tonnes FYM/ha/yr along with 125 per cent RDF and foliar spray of POSHAN exhibited superior characteristics such as higher moisture percentage (76.80 %), moisture retention capacity (93.30 %), crude protein (20.33 %), chlorophyll 'a' (1.57 mg/g) and 'b' (1.03 mg/g), and total chlorophyll content (2.57 mg/g). These results reveal the importance of nutrient management strategies, specifically emphasizing the significant role of organic and inorganic fertilizers combined with foliar applications in enhancing the nutritional and physiological aspects of mulberry plants. Such insights contribute significantly to optimizing agricultural practices for mulberry cultivation, thereby enhancing productivity and quality in sericulture systems. 

Bivoltine, Tree mulberry, Farm Yard Manure (FYM), Micronutrients, Graded level of nutrients.

Sericulture, a vital agro-based cottage industry in India which contributes significantly to the nation's economy and employment sector. Asia dominates global silk production where India ranks as the second-largest producer of mulberry raw silk. Mulberry (Morus spp.) serves as the primary nutritional source for silkworms (Bombyx mori L.) which is crucial for their growth and development. The quality of mulberry leaves is pivotal and directly impacting on silkworm health. Mulberry is a hardy, perennial, deep-rooted plant that produces a lot of biomass and grows throughout the year in the tropics. Mulberry being cultivated for many years and if grown without any scientific management results in a steady decline in leaf quality and production (Rashmi et al., 2009). However, traditional cultivation practices and environmental challenges such as irregular rainfall and droughts pose threats to mulberry leaf quality and production therefore tree mulberry planting has spread to plain  areas available crop on waste and degraded soils under extreme water stress conditions.

Sericulture relies heavily on nutrition therefore, it is imperative to apply the necessary fertilizer to the mulberry plant for the production of quality mulberry leaf (El-Kayat et al., 2013). Hence, this study aims to investigate the influence of graded level of nutrients that is combination of organic and inorganic fertilizers supplemented with foliar spray on quality of tree mulberry.

A study was conducted during 2022 at Krishi Vignana Kendra, Haradanahalli Farm, Chamarajanagara, in a well-established tree mulberry garden of variety V-1 with spacing of 6*6 feet under irrigated condition. The experiment was conducted using RBD with factorial concept consisted of sixteen treatments with three replications. After top pruning, the combination of manures and fertilizers which are below listed were applied and the cultural practices were followed as of Dandin and Giridhar (2014). Fourty-five days after pruning, the quality parameters such as leaf moisture percentage, leaf moisture retention capacity crude protein and chlorophyll contents were calculated by using the following formulas.

Treatment details

Treatment combinations

Moisture retention capacity after six hours was estimated

Moisture retention capacity (%) = 100 – Moisture loss (%)

Where, fresh weight is considered to be 100 per cent

Where,

A- Fresh weight of leaf

B-Leaf weight after six hours of harvest

Chlorophyll content in mulberry leaf was determined by the following procedure:

Where,

A663- Absorbance at a wavelength of 663 nm A 645- Absorbance at a wavelength of 645 nm

X –Total volume of the filtrate

n– Sample weight chemical analysis of soil

The per cent crude protein was estimated using the nitrogen content determined by the micro Kjeldahl method involving digestion, distillation and titration of the sample using the formula:

crude protein = (%) Nitrogen (%) × 6.25

Experimental details for silkworm rearing : To know the effects of feeding leaves from V-1 tree mulberry raised through the application graded level of nutrients on silkworm growth and yield, FC1 (CSR 6 × CSR 26) and FC2 (CSR 2 × CSR 27) silkworm hybrid was reared on these leaves by following standard silkworm rearing practices outlined by Dandin and Giridhar (2014). 

Silkworm feeding and bed cleaning : The late age silkworms were reared in shelf reared separately as per treatments by feeding three times a day with matured mulberry leaves of V-1 variety raised under different treatments. Bed cleaning was done twice during IV and V instars, by lifting unfed leaves and excreta of the silk worm. Optimum spacing was provided according to the age of the silk worms. After each bed cleaning and when all the silkworms settled for moulting, lime powder was dusted on silkworms following standard rearing practices Dandin and Giridhar (2014). 

Mounting and harvesting : Plastic Collapsible Mountages Were Used In The Experiment. The ripe worms were hand-picked from each treatment and replications were mounted separately treatment wise on the plastic collapsible mountages. Later on, the cocoons were harvested manually on the seventh day of mounting.

Fifth instar larval weight (g /10 larvae) : Weight of ten fifth instar silkworms was recorded by randomly picking silkworms from each replication of respective treatments on the fifth day of the fifth instar.

Moisture percentage, moisture retention capacity and crude protein. Scientific investigation of mulberry leaf parameters reveals a significant increase in quality parameters such as moisture percentage, moisture retention capacity (MRC) and crude protein content by the application of graded level of nutrients. Application of farmyard manure (FYM) at 40 t/ha/yr yielded highest moisture percentages (70.82%) compared to 20 t/ha/yr (69.61%), with nitrogen-phosphorus-potassium (NPK) application at 125% recommended dose recorded in the highest moisture content (73.58%). Foliar spray treatments exhibited enhanced moisture percentage (70.79%) compared to non-sprayed counterparts. Two-factor interactions revealed synergistic effects, with the highest moisture percentage achieved in A2 × B4 (75.68%). Similarly, FYM application at 40 t/ha/yr demonstrated superior moisture retention capacity (90.22%) compared to 20 t/ha/yr (86.70%), with the highest MRC observed with NPK at 125% RDF (91.09%). Foliar spray treatments displayed increased MRC (88.39%), while interactive effects showed peak MRC in A2 × B4 (93.24%). Crude protein content exhibited similar trends, with FYM at 40 t/ha/yr yielding the highest values (17.98%) compared to 20 t/ha/yr (17.31%), and NPK at 125% RDF recorded the highest crude protein (19.41%). Foliar spray treatments enhanced crude protein (17.96%), with interactive effects demonstrating peak crude protein in B4 × C2 (20.26%). The T16 treatment (40 T FYM/ha/yr + 125% RDF + Foliar spray of POSHAN) showcased superior performance across parameters. These findings underscore the importance of nutrient management strategies in optimizing mulberry leaf quality for sericulture (Table 1).

The results are in conformity with the findings of Mishra et al. (1996) found that using NPK fertilizer dose of 225:150:150 kg/ha/yr and adopting top-clipping resulted in good quality mulberry leaves in the S-54 variety with high moisture (79.69 %) and protein (25.19 %) contents. Bhaskar et al. (2003) found that irrigated M-5 mulberry with varying amounts of N (200-280 kg /ha/ yr), P (80-140 kg /ha/ yr) and K (80-140 kg /ha/yr) recorded that application of 280:80:80kg NPK/ha/yr recorded higher growth characteristics and leaf moisture content than in control.

Table 1: Influence of graded level of nutrients on moisture percentage, moisture retention capacity (%) and crude protein (%) of tree mulberry.

Note: (NS– Non-Significant)

Similar results were obtained by Fotedar et al. (1988) who found out the impact of various nitrogen levels (0, 100, 200, 300, and 400 kg ha-1 yr-1) on mulberry quality (Table 2).

Table 2: Influence of graded level of nutrients on Chlorophyll ‘a’ (mg/g), chlorophyll ‘b’ (mg/g), total chlorophyll (mg/g) content.

Note: (NS– Non-Significant)

Larval progression and larval weight. The research investigated larval progression (%) in FC 1 and FC 2 breeds of silkworm Bombyx mori L. under varying treatments. Notably, FYM application at 40 t/ha/yr resulted in higher larval progression compared to 20 t/ha/yr in both breeds (96.38% and 96.79%, respectively). Similarly, NPK application at 100% RDF recorded the highest larval progression, with values of 97.25% and 97.67% in FC 1 and FC 2 breeds, respectively. Foliar spray application demonstrated increased larval progression compared to non-application, with values of 95.88% and 96.44% in FC 1 and FC 2 breeds, respectively. Two-factor interactions revealed the highest larval progression when FYM was combined with NPK, with values of 98.00% and 98.13% in FC 1 and FC 2 breeds, respectively. FC 2 breed exhibited superior larval progression compared to FC 1 breed across treatments. Specific treatment combinations, such as T14 and T15, showed particularly high larval progression in both FC 1 (98%) and FC 2 (98.74%) breeds. Overall, these findings suggest that FC 2 breed displays greater hardiness and better larval characteristics than FC 1 breed under certain treatment conditions.

The study investigated the impact of agricultural inputs on larval weight and progression in two silkworm breeds, FC 1 and FC 2. Larval weight increased progressively with instar growth, with the final two instars contributing around 90% of body weight. Application of farmyard manure (FYM) at 40 t/ha/yr resulted in the highest larval weight (32.34 g/10 larvae) compared to 20 t/ha/yr (31.11 g/10 larvae) in FC 1 breed, while similar trends were observed in FC 2 breed with 39.08 g/10 larvae. Higher doses of NPK and foliar spray treatments also led to increased larval weight, with NPK at 125% RDF resulting in 34.95 g/10 larvae and 41.50 g/10 larvae in FC 1 and FC 2 breeds, respectively. Interaction effects between FYM, NPK, and foliar spray showed varying impacts on larval weight, with certain combinations yielding the highest weights, such as A2×B4 level (35.65 g/10 larvae and 41.93 g/10 larvae in FC 1 and FC 2 breeds, respectively). FC 2 breed demonstrated superior hardiness and recorded higher larval weights compared to FC 1, with treatment T16 (40 T FYM/ha/yr + 125% RDF + Foliar spray of POSHAN) resulting in the highest larval weight (43.67 g/10 larvae) among all treatments. Even though larval progression (%) was higher among many treatments in both races, the Larval weight was found to be highest only in the T16 (40 T FYM/ha/yr + 125 % RDF + Foliar spray of POSHAN). This could mean that the larval progression (%) is not directly contributing to the larval weight rather the treatments are influencing the larval weight (Table 3).

Sannappa et al. (2003) found that when silkworms were fed mulberry at 5 feeds per day and raised with N at 125 kg/ha/yr, they had higher fifth instar larval weight (43.83 g/10 larvae), larval survival (92.33 %), ERR (89.50 %) and cocoon yield (38.19 kg/50 DFL's) with shorter total larval duration (25.32 days) than when they were fed 4 and 3 feeds per day. 

Mulberry growth and yield were significantly increased after application of NPK @ 400:180:25 kg/ha/yr, as were larval weight, larval duration, and moulting duration. The cocoons that were spun were of good quality (Sreerama, 2006). The study was carried out to ascertain the performance of silkworm (B. mori L.) double hybrid fed on leaf raised through splitting the recommended dose of chemical fertilizers. The weight of ten mature larvae was recorded to be higher (55.40 g) in treatment T14 (N4P1K2) being statistically at par with 55.38, 55.31 and 54.90 grams found in treatments T13 (N4P1K1), T16 (N4P2K2) and T15 (N4P2K1), respectively. Cocoon yield per 10,000 larvae by number was recorded highest 9133.33 in T14 (N4P1K2) treatment which was found statistically at par with 9100.00 and 9066.67 in treatments T13 (N4P1K1) and T16 (N4P2K2) respectively (Nazim et al., 2020).

Table 3: Influence of graded level of nutrients on Larval progression (%), test weight (g/10 larvae) of FC 1 and FC 2 bivoltine silkworm breeds.

Note: (NS – Non-Significant)

A comprehensive scientific investigation into mulberry leaf parameters reveals significant influences on moisture percentage, moisture retention capacity (MRC), crude protein content, and chlorophyll content by the combined application of fertilizers and these are the crucial factors for optimizing mulberry plant productivity in sericulture. Application of farmyard manure (FYM) at 40 t/ha/yr demonstrates superior performance across parameters, notably yielding highest moisture percentages, MRC, crude protein content, and chlorophyll levels, with synergistic effects observed particularly in combined treatments with NPK at 125% recommended dose of fertilizer (RDF) and foliar spray of micronutrients (POSHAN), highlighting the pivotal role of nutrient management strategies in enhancing mulberry leaf quality and photosynthetic efficiency.

The larval progression (%) of FC1 breed peaked at 98% in treatments T8, T13, T14, T15, and T16, while FC2 breed showed its highest progression in treatments T8 (A1B4C2 – 20 T FYM/ha/yr + 125% RDF + Foliar spray of POSHAN), T14 (A2B3C2 – 40 T FYM/ha/yr + 100% RDF + Foliar spray of POSHAN), and T15 (A2B4C1 – 40 T FYM/ha/yr + 125% RDF) at 98.74%. Non-significant differences were observed between these treatments for both breeds. Regarding larval weight, significant differences were noted in FC2 breed, whereas FC1 breed showed non-significant differences.