Evaluation of Fertilizer-manure Blocks as a Slow Release Fertilizer Formulation for Okra [Abelmoschus esculentus (L.) Moench]

Kerala is a state with tropical humid climate and heavy rain fall leading to leaching of bases and results poor soil fertility. Thus adequate quantities of nutrients have to be supplied through appropriate nutrient delivery techniques. There are different nutrient delivery techniques for ensuring adequate plant nutrition which include soil application, foliar application of nutrients and nutrient mixtures, fertigation by using water soluble fertilizers etc. Effective fertilizer use is the key factor that determine agricultural production. Direct application of fertilizer nutrients to the soil cannot ensure high nutrient use efficiency (NUE) and nutrient security for the crops due to the physico-chemical properties of the soil as well as the environmental factors which may lead to nutrient loss from the system. Loss of applied nutrients from the site of application not only cause harmful effect on the environment but also affect the socio-economic situation of the farmers because fertilizers are one of the costliest inputs in agriculture. To overcome this, targeted application of plant nutrients is necessary and this can be ensured by using slow or controlled release fertilizers.

According to Morgan et al. (2009) slow/ controlled release fertilizer formulations offer agricultural producers the opportunity to increase nutrient use efficiency, especially in soils with very low cation exchange capacity. Incorporation of organic manures have some additional advantages like improving the physical, chemical and biological properties of soil. Kumar et al. (2012) developed a customized formulation, organic matrix entrapped urea in granular form by mixing natural materials such as  cow dung, rice bran, neem leaf powder and clay in 1:1:1:1 along with half of the recommended dose of commercially available soluble for rice (Oryza sativa L. cv. Basmati) and it was found effective method for improving growth, productivity and nutritional status of rice  and enrichment in soil fertility. They suggested that organic matrix entrapped urea, a biodegradable slow release fertilizer, can be attempted to replace the conventional use of soluble urea in rice. 

Okra, Abelmoschus esculentus (L.) Moench is an important vegetable crop widely grown in tropical, subtropical and warm temperate regions of the world. The fruits or pods are harvested when immature and are used as vegetables. Okra is a fertilizer responsive vegetable crop. Since okra is a vegetable crop with indeterminate growth pattern it has simultaneous vegetative as well as reproductive growth. Abbasi et al., (2010) found that foliar application of multinutrients supplement plant nutrition in integration with soil applied chemical fertilizers improved growth traits of okra such as days to flowering, plant height, number of branches per plant, number of fruits per plant, fruit length etc.

This study is mainly focused on the effect of fertilizer-manure blocks of different sizes and varying dosage of fertilizers on yield and yield characteristics of okra plant.

The fertilizer-manure blocks of proportion- Coirpith- 35%, Cowdung- 25%,Vermicompost-13%, Groundnut cake- 10%, Neem cake 10%, Zeolite- 2%, Humic acid- 5% showed slow release pattern of nutrients as compared to sole use of fertilizers in a laboratory incubation study conducted at Regional Agricultural Research Station, Pattambi. No adhesive was used for formulating the blocks. The nutrient contents of various component materials used for formulating the fertilizer-manure blocks are given in Table 1.



The best proportion (Treatment) selected based on the laboratory incubation experiment was used for the pot culture study conducted at Regional Agricultural Research Station, Pattambi during the year 2017-18; to investigate the efficiency of fertilizer-manure blocks on growth and yield of okra (variety Arka Anamika).

For pot culture study fertilizer- manure blocks was prepared in two dimensions (100g and 25 g blocks) using three different dosages (100 per cent POP (Package of Practices, Kerala Agricultural University), 50 per cent POP and 25 per cent POP) of fertilizers for the crop. The per plant dosage of fertilizers was calculated based on the POP and ad hoc POP recommendations of primary, secondary and micro nutrients and were used for formulating single block. Combinations of the various dosages of recommendations and sizes of the blocks were taken as T1-T6. Hence the experiment consisted of a total of 11 treatments with 3 replications such as T₁: Blocks of size 100 g with nutrients as per 100 per cent  POP @ 1 block per grow bag, placed below the level of planting, T₂: Blocks of size 100 g with nutrients as per 50per cent POP @ 1 block per grow bag, placed below the level of planting, T₃: Blocks of size 100 g with nutrients as per 25 per cent POP @ 1 block per grow bag, placed below the level of planting, T₄: Blocks of size 25 g with nutrients as per 100 per cent POP @ 4 blocks per grow bag, placed on 4 sides of the plant at soil surface, T₅: Blocks of size 25 g with nutrients as per 50 per cent POP @ 4 blocks per grow bag, placed on 4 sides of the plant at soil surface, T₆: Blocks of size 25 g with nutrients as per 25 per cent POP @ 4 blocks per grow bag, placed on 4 sides of the plant at soil surface, T₇: T₃ + 50 per cent POP recommendation as top dressing, T₈: Nutrients as per general POP of  KAU, T9: Nutrients as per soil test based POP recommendation, T₁₀ : Control( Organic manure as per POP of KAU ) and T11: Absolute control.

The experiment was laid out in a completely randomized design with 11 treatments and three replications. Five pots were maintained in each replication. Days to flowering, plant height, number of leaves per plant, number of branches per plant, total number of fruits per plant, fruit length, fruit girth, total fruit yield per plant and number of seeds per plant are the observations recorded during pot culture study.

Effect of treatments of fertilizer-manure block on yield and yield characteristics (Table 2)
 
Fruit yield, fruit number, fruit length, fruit diameter and number of seeds per fruit were recorded from the Okra crop and the data is presented in the table II. Highest fruit number was recorded by the treatment T₇ where in 25% of the recommended nutrients based on KAU POP recommendation was given as fertilizer-manure block and 50% as top dressing. However it was found to be on par with the treatments T₈ (Nutrients as per KAU POP recommendation) and T₉ (Nutrients as per soil test based recommendation) i.e. savings of 25% recommended fertilizers is obtained where fertilizer-manure blocks was used. This can be attributed to reduced loss of nutrients from the fertilizer-manure block owing to its slow release of nutrients and hence fertilizer use efficiency (FUE) is improved to a greater extent. Kiran et al., (2010) also suggested such improvement in FUE on use of slow release fertilizer technology.



More over the slow release nature of the fertilizer-manure block can supply the nutrients in accordance with the crop growth resulting in reduced leaching and increased plant uptake. Venkadeswaran and Sundaram, (2016). conducted an experiment on nutrient uptake of hybrid okra under drip fertigation plot receiving daily fertigation of water soluble fertilisers recorded higher fruit N, P and K uptake than the crop receiving daily fertigation of conventional fertilizers. Akter et al. (2017) reported that the use of fertilizers and organic manures in combination improved crop growth and yield in tomato. Similar results of use of fertilizers and organic manures were reported by Sharma and Singh (2011) in Brassica juncea. Singh et al., (2013) recorded the parity of yield between full recommended dose of urea and diammonium phosphate (DAP) and organic matrix entrapped urea and DAP containing ¼th of the recommended dose.

The yield attributes such as number of fruits per plant, fruit length and girth showed the similar trend as that of the fruit yield. Treatments T₄, T₉ and T₇ were having highest number of seeds per fruit, which can be attributed to the graded supply of all nutrients for seed filling and yield (Table 2).
 
Effect of fertilizer-manure blocks on Biometric parameters (Table 3)
 
The fertilizer-manure blocks made with different fertilizer dosages and in different size placed in grow bags of Okra crop showed significant difference in biometric parameters and the data is presented in theTable 2. Pant height, number of leaves per plant and number of branches per plant showed significant difference among treatments. The results revealed that biometric parameters are in general higher for the treatment T₇ where 25% of the recommended nutrients was applied in the form of 100 g fertilizer manure block as basal and 50% of the recommended nutrients was applied as fertilizer as top dressing at 1 month after planting.



The comparison of size and placement of the different fertilizer-manure blocks revealed the superiority of the 100 g block placed below the planting depth over 4 numbers of 25 g blocks placed around the plant just below the surface (Plate 1).



This may be due to the fact that leaching of nutrients from the 25 g blocks placed just below the surface occurred before the complete establishment of the root system. However the root system might have entered directly in to the 100 g blocks resulting in effective utilization of the nutrients entrapped inside the fertilizer-manure blocks. This is very clearly visible in the Plate 2.



The use of organic components along with fertilizers slow down the release of nutrients which can be taken as a point to explain the reduction in fertilizer recommendation needed when the fertilizer manure blocks was used. Trinh et al. (2022) significant studied the effect of organic Fertilizer and planting type on growth and yield of Curcuma aromatica. Puri (1999) reported the effect of neem on inhibition of nitrification. Neem cake is a component in fertilizer-manure block formulated in the study.

The treatments showed significant influence on number of days taken to flowering. Shubham Chawla et al., (2018) conducted a field study on effect of dates of sowing and nitrogen levels on growth and yield of okra and reported remarkable significant influence on all growth attributes, flower characters and yield parameters. Significantly early flowering was observed in the treatment T₈ which received nutrients as per KAU POP recommendations and it was on par with all treatments except T₄, T₁ and control. Shukla et al., (2018) also reported that, the occurrence of days to flowering in okra is directly related to the fertility status of the soil.

The control and absolute control treatments T₁₀ and T₁₁ had took more days to flowering (34.83 and 36.33 days) and this may be due to in adequate nutrient availability in these treatments.
 

The results of the pot culture study revealed that fertilizer manure blocks showed significant influence on the growth and yield of okra. Fertilizer-manure blocks can be used in Okra as an efficient and sustainable nutrient management technique. Twenty five per cent reduction in the recommended dose of nutrients is achieved by using fertilizer-manure blocks. Among various treatment, treatment with 25% of the recommended nutrients applied in the form of 100 g fertilizer-manure block and 50% as topdressing 1 month after planting was the best treatment which recorded highest yield (457.9 g), high nutrient use efficiency, B:C ratio greater than 1(1.26) and saves 25% of the recommended nutrients. Thus fertilizer-manure block is a slow release fertilizer capable of ensuring long term nutrient availability and by adopting this technique we can reduce the fertilizer load in the soil and hence improve nutrient use efficiency and productivity. In future, studies can be undertaken to standardize controlled release fertilizer-manure formulations in open field conditions and in various crops including long duration crops.
 

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