Introduction

In Sarawak, Malaysia, pepper (Piper nigrum L.) was planted by smallholders as one of the crops to supplement their farm incomes. Its method of cultivation involved excessive chemical fertilization as pepper is a high nutrient-demanding crop (Yap 2012; Kho and Chen 2017; Kumar and Swarupa 2017). This system gave good yields but this was achieved at a considerably high cost of production (Paulus and Anyi 2011). According to the Malaysian Pepper Board, MPB (2018), low pepper prices and increasing production costs in recent years have burdened pepper farmers and made pepper cultivation unattractive as smallholders had started shifting from pepper to other crops such as pineapples and durian cultivation. Hence, introducing organic fertilizers is seen as a viable alternative to reduce use of inorganic fertilizers and at the same time providing farmers with sustainable and low-cost pepper cultivation package (Paulus 2011).

In pepper cultivation, immature vines (Fig. 1) are commonly referred to vines which are 3 years and below from the day of first planting. Compared with mature vines (Fig. 1), immature vines required careful attention in the first 2 years after initial planting for them to grow well. Together with formation pruning and flower spike removal in the first year (Sim and Paulus 2011), fertilization of young pepper vines requires balanced formulation of primary nutrients, namely, N, P, and K to create canopies. Currently, inorganic compound fertilizer formulations which are in use for immature vines are 9:9:9 and 15:15:15 (Paulus 2011). According to Paulus and Anyi (2011), there are profound differences in the agronomic practices between immature and mature vines such as fertilizer use, labor requirements, and fertilization costs. These differences affect the overall production costs. To date, enhancing food security through organic farming in Malaysia is not a well-established option because of lack of technical knowledge in the required subject. The desired effects for applying organic fertilizers to soils can vary, at least initially. In some soils, a single application may be enough to produce expected results, whereas for other soils, repeated applications may be ineffective (Javaid and Bajwa 2010).

Fig. 1
figure 1

Immature and mature pepper vines

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Hence, proper and regular addition of organic amendments is often an important part of any strategy to introduce organic farming (Zamora and Calub 2016). To this end, there is a strong premonition that application of organic fertilizers can ensure productive pepper farming, clean environment, increased profits of pepper growers, and at the same time increased production of affordable healthy and fresh organic produce.

Because of the afore-stated reasons, a study to assess immature pepper’s performance following adoption of organic amendments was conducted. Therefore, the objective was to study the effects of organic amendments on selected soil properties, morphological characteristics, and yield of immature vines and its economic viability on immature pepper production.

Materials and methods

Study site

The study was conducted at Kampung Jagoi, Duyoh, Serikin, Sarawak with an area coordinate of 1.341265, 110.026002. The study plot was a newly cleared 2-year-old pepper farm with a size of approximately 0.5 ha. The Piper nigrum var. Kuching was chosen for this study because it is the most common variety cultivated in Malaysia. Immature pepper vines are vines that are less than 3 years old from the day after field transplanting. For the purpose of this study which was to obtain at least 2 years of harvesting data, uniform and healthy fruit-bearing premature pepper vines which were 2 years of age were selected. To prevent significant variation in data, only vines planted on flat land were selected. Pepper vine planting using standard farm practice recommended by the Malaysian Pepper Board (MPB) was used in this study. The study started in July 2016 and ended in February 2019.

Experimental soil

The soil at the planting site was previously surveyed by the Department of Agriculture, Soil Branch, Kuching, Sarawak and it was named Bemang series (Soil Survey Staff 2000). Bemang series is an alluvial soil; fine loamy/silty, siliceous/mixed, acid, isohyperthermic, Typic Dystroepts, alluvium from sedimentary rocks (Paramanathan 2000).

Experimental design and treatments

A randomized complete block design (RCBD) with five treatments and five replications resulting in a total of 25 experimental plots was used for this study. The treatments used in this study (Table 1) were (i) F0—control, (ii) F1—fermented plant juice (FPJ), (iii) F2—fermented plant juice incorporated with biochar and compost (FPJBC), (iv) F3—fermented fruit juice (FFJ), and (v) F4—fermented fruit juice incorporated with biochar and compost (FFJBC). The FPJ and FFJ were prepared monthly to ensure only fresh batches of fermented juices were applied to the soils. From beginning of the experiment, FPJ and FFJ were applied once a month.

Table 1 The details of the treatments used in this study—description, composition, and rate of application
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Compound fertilizer (15:15:15) application

For immature vines, a 15:15:15 compound fertilizer was applied in two narrow bands just below the outer canopy of the vine. The fertilizer was placed in a shallow trench made using a rake and then covered over with a thin layer of soil. Frequency and rate of the fertilizer application are shown in Table 2.

Table 2 Rate of compound chemical fertilizer application for immature vines (Paulus 2011; MPB 2017)
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Fermented plant juice production and application

The FPJ was produced monthly based on the method of Zamora and Calub (2016). The FPJ is composed of plants with fresh, juicy, and succulent parts including “kangkong” or water spinach, Chinese mustards, banana stem, tapioca, bamboo leaves, and green grasses. For application that covers 100 immature pepper vines, 100 mL of FPJ was mixed in 16 L of water after which the mixture was sprayed directly onto mounded area of the soil until the soil was relatively moistened. The FPJ was applied early in the morning and late evening to avoid losses.

Fermented fruit juice production and application

The FFJ was produced monthly based on the method of Zamora and Calub (2016). The FFJ consisted of discarded fruits including banana, papaya, pumpkin, and pepper berries. Approximately 100 mL of FFJ was mixed in 16 L of water and afterwards, the mixture was sprayed directly to the mounded area of the soil until the soil was relatively moistened. The FPJ was applied early in the morning and late evening to avoid losses.

Biochar production and application

The method of Wahi et al. (2015) was used to produce biochar from palm kernel (PK) shell which was obtained from Kota Samarahan, Sarawak, Malaysia. The PK biochar was applied to the soil before spraying of the fermented juices (Zamora and Calub 2016). For immature vines, approximately a 1 kg of PK biochar was broadcast on top of mounded area of the soils. The soils were then loosened and mixed with PK biochar using a hoe. Application of PK biochar was done once a year.

Compost production and application

The method for compost production which involved fermented plant juice (FPJ) application to accelerate composting process was adapted from Zamora and Calub (2016). The raw materials which were used in producing the compost were leaves from tapioca, bamboo, vegetables, and banana plants, grass chippings, discarded fruits, rice straw, rice hull, and corn stalks. Approximately 2 kg of compost was heaped on top of mounded areas of the soil. The application of the compost enables it to act as mulch and also as a soil conditioner. The compost application was done every 3 months from the onset of the experiment.

Organic soil amendment total NPK analysis

An analysis was done on fermented juices, biochar, and compost to determine its total N, P, and K using standard procedures (Aizawa et al. 2010).

Selected soil physical property determination

Before the start and during the course of the experiment, soil samples were analyzed for bulk density, porosity, and soil texture according to the method by Edwards (2010).

Selected soil chemical property determination

Samples were collected with an auger at a depth of 0–15 cm and analyzed for pH, electrical conductivity (EC), cation exchange capacity (CEC), total organic carbon (TOC), total nitrogen (N), C/N ratio, available phosphorus (P), exchangeable potassium (K), exchangeable calcium (Ca), exchangeable sodium (Na), and exchangeable magnesium (Mg) according to the method by Edwards (2010).

Soil biological property determination

At the end of each harvesting period, on-site soil respiration was conducted following the method of DiCristina and Germino (2006), whereas soil samples were collected for total microorganism count analysis following the method of Edwards (2010).

Pepper morphological measurement

Before annual harvest of pepper berries, measurement on average length of fruit spike and fresh berry yield was recorded during the harvesting months, whereas measurement of leaf area index (LAI) was obtained according to the method by Bianco et al. (2005).

Economic analysis

Data on the yield can be used to measure the economic viability in pepper cultivation (Paulus and Anyi 2011). At the end of the assessment period (2018), fresh berry yield was used for the economic analysis. Black pepper yield data were then obtained by calculating the 33% conversion rate of the fresh berry yield results. The black pepper yield data were used to estimate the first year to the tenth year of pepper cultivation. Benefit-cost ratio (BCR), net present value (NPV), internal rate return (IRR), gross income (GI), total production cost (TPC), accumulated net cash flow (ANCF), year of payback, and cost of production (COP) calculations were based on the formula of Paulus and Anyi (2011). The calculation took into account cost of fertilizers, dolomites, weedicides, pesticides, miscellaneous farm implements, maintenance of farm, harvesting, and processing for an estimated 10-year period.

Statistical analysis

Data were analyzed using one-way analysis of variance (ANOVA) and the SPSS software (version 15) was used as the statistical software. Tukey’s honest significance difference (HSD) test, at α = 0.05 level of significance, was done to compare treatment means.

Results and discussion

Chemical composition of organic soil amendments

The chemical composition of organic soil amendments is presented in Table 3. The result shows that the total N, P, and K composition of the fermented juices and biochar were significantly lower when compared to that of the compost. Based on the results in Table 3, the estimated amount of total N, P, and K for treatment F1—FPJ and F3—FFJ was very low, which were less than 1% for each of the aforementioned macro-nutrient. Meanwhile, the estimated amount of total N, P, and K in treatment F2—FPJBC was 1.62, 10.23, and 8.12% respectively. Almost similar as treatment F2, the estimated amount of total N, P, and K in treatment F4—FFJBC was 1.55, 10.23, and 8.15% respectively This observation is consistent with those of Kimpinski et al. (2003) and Zuraihah et al. (2012) who documented that soil organic amendments such as fermented juices and biochar are primarily used as a soil conditioner and not as a fertilizer because they are rather high in organic content (90‑95%) but generally low in macro- and micro-nutrients compared with commercial fertilizers. As the fermented juices are in liquid form, Green (2015) stated that moisture content is a factor that reduces or dilutes the nitrogen, phosphorus, and potassium concentrations. This result also suggests that most of the macro-nutrients that are available for the plant were derived from the compost. Because of this, the fermented juices only treatments (F1 and F3) deliver lower amount of NPK to the soil than the combined fermented juices, biochar, and compost treatments (F2 and F4). Generally, high-quality composts have full spectrum of plant nutrients, although the exact amounts vary from sample to sample (Schulz and Glaser 2012). Well-rotted compost is rich in macro- and micro-nutrients (Sharma et al. 2017). Marcote et al. (2001) opined that because composts make macro- and micro-nutrients more available to plants, they are nature’s ultimate organic fertilizer and soil conditioner.

Table 3 Total NPK of fermented juices, biochar, and compost used in this study
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Selected soil physical properties

Effects of the organic soil amendments on soil bulk density and porosity are presented in Table 4. Except the soils with FPJ, compost, and biochar (F2), bulk densities were high with other treatments (first year of assessment) because organic amendments do not significantly affect hardness of soils if they are applied in less than a year (Tanaka et al. 2008). Furthermore, the soil bulk density of the pepper farm is related to initial land preparation and subsequent soil maintenance and in pepper cultivation, soils are compacted during land preparation. In the second year of assessment, the treatments with compost and biochar (F2 and F4) showed the lowest soil bulk density followed by the treatments with only FPJ and FFJ (F1 and F3), whereas the chemical fertilizer (F0) treatment showed the highest soil bulk density.

Table 4 Effects of organic amendments on soil bulk density and porosity of immature vine farm for 2 years of observation
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At the end of the study, soil porosity results showed similar trend as soil bulk density where F2 and F4 demonstrated higher soil porosity compared with those of F1, F3, and F0. These findings also suggest that prolonged use of composts and biochars can minimize soil compaction to improve soil aeration and drainage. These organic amendments are reputed for improving the arrangement of sand, silt, and clay hence maintaining the soil structure of the pepper farm involved in this present study (Wahi et al. 2015; Schulz and Glaser 2012).

Zuraihah et al. (2012) also attributed significant improvement in soil porosity and bulk density following application of fermented juices to biochar and compost compared with fermented juices only. The authors added that decomposition of organic matter caused by beneficial microbes in fermented juices caused the soil porosity and bulk density improvement. This suggests that mixture of fermented juices, biochar, and compost can increase meso- and macro-pores because of improved aggregation and stabilization of soils through the activities of soil micro- and macro-organisms (Partanen et al. 2010). Sim and Paulus (2011) opined that, having soils with ideal bulk density is essential for root growth and development of immature pepper vines as they enable plant root extension with less restrictions on available nutrients and water.

Selected soil chemical properties

Soil pH, EC, and CEC of the organic farm with immature pepper vines are shown in Table 5. Knowing soil pH is important for crop cultivation because many plants and soil organisms prefer slight alkaline or acid conditions thrive. Wong (1986) mentioned that pepper can be grown on a wide variety of soils, but deep and well-drained clay loam soils which are rich in organic matter with a pH range of 5 to 5.5 are preferred. Based on the soil pH (water) of the pepper farm in 2017 and 2018, the treatments with fermented juices, composts, and biochar (F4 and F2) significantly improved soil pH, followed by the soils with only the fermented juices (F1 and F3). The control treatment (F0) showed the lowest soil pH in 2017 and 2018. A similar trend was observed for soil pH in KCl in 2017. In 2018 however, the effects of F0, F1, and F3 on soil pH were not significantly different but the fermented juices, biochar, and compost (F2 and F4) improved soil pH.

Table 5 Effects of organic amendments on soil pH, electrical conductivity, and cation exchange capacity of immature vine farm for 2 years of observation
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Zuraihah et al. (2012) noted that fermented juices in organic farming do not play any role in increasing soil pH because decomposition of organic matter by beneficial microorganisms rather increases soil acidity. In this present study, the decrease in soil acidity could be attributed to the high pH of the biochar and compost used. Hunt et al. (2010) pointed out that incorporating biochar and compost in soils can increase soil pH because of their liming effects. These findings agree with those of Fischer and Glaser (2012) who attributed increase soil pH in biochar-amended soil to ash accretion. They further explained that ash residues are highly dominated by carbonates alkali and alkali earth metals. Agegnehu et al. (2016) also reported that composts have liming effect because of their richness in alkaline or base cations such as Ca, Mg, Na, and K which were liberated from organic matter through mineralization. Lawrinenko (2014) also added that increase in soil pH following application of organic amendments was due to organic anions in such amendments, and this was suggested by the concentration of excess cations over inorganic anions.

In 2017, soil EC of F0, F1, and F2 were similar but significantly higher than those of F3 and F4. However, in 2018, EC of the inorganic fertilizer (F0) was significantly higher than in the plot amended with organic fertilizers (F1, F2, F3, and F4). These findings corroborate those of Huerta-Pujol et al. (2010) who also reported increase in soil EC following application of inorganic fertilizers. The possible explanation for increase in soil EC following application of inorganic fertilizers was due to the high contents of soluble salts of the fertilizers (Rajkovich et al. 2011). Sanchez et al. (2011) also observed that soil pH and EC were inversely related and because of this, they concluded that high pH soils will be low in EC.

In 2017, CEC of the plot amended with organic fertilizer treatments (F1, F2, F3, and F4) were significantly (P < 0.05) lower than that of the inorganic fertilizer (F0) (Table 5) but the opposite was true in 2018. The increase in soil CEC in 2018 was in the order of F4 > F2 > F0 > F3 > F1. Overall, the fermented juices with biochar and compost improved soil CEC with increasing time because the porosity and surface area of biochars increase their surface sorption ability and base saturation (Glaser et al. 2001). Atiyeh et al. (2000) and Marcote et al. (2001) indicated that composts can increase CEC because they are composed of stabilized organic matter which is rich in functional groups such as carboxylic and phenolic acid groups. These functional groups are noted for high negative charges and reputed for holding positively charged nutrients such as ammonium, K, Ca, Mg, and Na in soils.

Effects of different organic amendments on soil total organic carbon (TOC), total N, C/N ratio, and available P are presented in Table 6. In 2017 and 2018, TOC of the soils with fermented juices, biochar, and compost (F2 and F4) were significantly higher than those of inorganic fertilizer (F0) and fermented juices alone (F1 and F3), suggesting that application of biochar and compost to soils increases TOC. A report by the International Biochar Initiative (2012) which stated that biochar and compost applications to soils can enhance C accumulation and sequestration is in agreement with this present finding. Javaid and Bajwa (2010) attributed higher TOC levels in biochar and compost amended plots to the fact that these organic materials have significant impact on mineralization rates to increase soil C, unlike the inorganic fertilizers whose effects are less pronounced. In many compost studies, addition of organic plant residues increased soil microbial biomass and activities leading to increase in organic matter and soil organic C levels (Kimpinski et al. 2003; Partanen et al. 2010; Sharma et al. 2017).

Table 6 Effects of organic amendments on soil total organic carbon, total nitrogen, C/N ratio, and available phosphorus of immature vine farm for 2 years of observation
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Regardless of year, total N of the soil with inorganic fertilizers (F0) was significantly higher than those under organic amendments (F1, F2, F3, and F4) (Table 5). At the end of this present study, F1, F2, F3, and F4 increased soil total N by 30%, 25%, 11%, and 11%, respectively and these values were comparable to that of Bemang series (total N—0.10%). The inorganic fertilizer used in the immature pepper vine cultivation was NPK 15:15:15 which is higher in N than the organic amendment treatments used in this present study. Agegnehu et al. (2016) documented that inorganic compound fertilizer such as NPK 15:15:15 has significant amounts of readily available primary plant nutrients and variety of essential trace elements. Thus, inorganic compound fertilizers can be defined as multi nutrient fertilizers (Yap 2012). Nevertheless, the diverse beneficial properties of organic soil amendments for soil amelioration outreach their nutrient contents (Higa 2000; Khaliq et al. 2016). Although composts are rich in readily available nutrients for optimum plant use, their fertilizing effects last longer than inorganic fertilizers because of gradual decomposing and release of plant nutrients (Hashemimajd et al. 2004). Sharma et al. (2017) ascribed this to the existence and different intensity of various binding forms within the organic matrix, resulting in partial immobilization of nutrients. This partly explains why composts are able to minimize leaching of plant nutrients than soluble inorganic fertilizers (Hashemimajd et al. 2004; Zimmermann 2008). Rajkovich et al. (2011) stated that lower N in soils amended with microbe-based liquid organic fertilizers and compost was due to N immobilization by microbes. Doran and Zeiss (2000) documented that accumulation of N in microbial biomass and accumulation of N in by-products of microbial activity were the types of mechanisms that immobilize N in soils.

Irrespective of year, the effects of treatments on soil C/N ratio were similar. Soils with fermented juice, biochar, and compost showed higher C/N ratios in year 2017 (F2—23.88 and F4—22.71) and 2018 (F2—22.38 and F4—22.14). In 2017, the soils with only fermented plant juice (F1) and fermented fruit juice (F3) recorded C/N ratios of 14.69 and 13.20, respectively. In 2018, F1 and F3 showed C/N ratios of 11.75 and 11.60, respectively. In 2017 and 2018, the C/N ratios of the inorganic fertilizer (F0) were the lowest (2.20 and 1.62, respectively). Unlike F0, F2, and F4, the findings on F1 and F3 were in accordance with those of Huerta-Pujol et al. (2010) who also reported optimum balanced C/N ratio (10 to 12) for soils amended with plant residue composts because of organic matter mineralization over immobilization. Nonetheless, a similar study which was carried out by Lawrinenko (2014) showed an increase in C/N ratio from 10.7 to 22.2 in the second year after biochar and compost application. This observation can be explained based on depletion of N reserve, probably because of plant N uptake. However, there are often other explanations for such increase in C/N ratio. It is well known that if an organic amendment with high C/N ratio is added to soils, the soil microbes compete with plants for soil N and this causes N immobilization (Doran and Zeiss 2000; Rajkovich et al. 2011). On low C/N ratio in soils amended with inorganic fertilizer, Sharma et al. (2017) associated it to low concentration of easily decomposable C compounds and a larger N quantity in respect to that required by microbial biomass. This leads to net N mineralization to release of inorganic N. To enable microorganisms to decompose organic residues, Sharma et al. (2017) added, N of the residues has to be assimilated in an amount determined by the C/N ratio of microbial biomass. More specifically, the amount of N required by microorganisms should be 20 times smaller than that of C.

During the first and second years of assessments, available P of the soil with the inorganic fertilizer (F0) was significantly higher than those under organic amendments (Table 6). This finding is comparable to that of Yap (2012) who also stated that inorganic NPK fertilizers are superior to any organic amendment because of their higher essential nutrients such as P. It was also found that the effects of F1, F2, F3, and F4 on available P in year 2017 were similar. However, in 2018, the available P in the soils with FFJ, biochar, and compost (F2 and F4) were significantly higher than in those with FFJ only (F1 and F3). The higher soil available P of F2 and F4 compared with the treatments with only fermented juices (F1 and F3) was due to the biochar and compost in F2 and F4. This finding also agrees with that of Fischer and Glaser (2012) who also reported that the combined use of biochars and composts as soil conditioners usually housed phosphate solubilizing microbes and at the same time stimulates their activities to release soil available P. Zimmermann (2008) also mentioned that it was possible to enhance effectiveness of phosphate solubilizing microbes by adding biochar, or a similar material with tiny perforations, in which the microbes are housed. Sharma et al. (2017) added that composts which are inoculated with beneficial microorganisms from fermented fruit juices are good sources of nutrients for crops because they are able to promote mobilization of insoluble nutrients and activate phosphate solubilizing microbes in amended soils. Besides, it was known that the fermented juices contained many of these microbes including Aspergillus sp., Bacillus sp., Lactobacillus sp., Sporosarcina sp., Anaerobacillus sp., Trichococcus sp., Talaromyces sp., and Penicillium sp. which are capable of transforming insoluble P to soluble forms for readily plant uptake or use (Talaat et al. 2015; Yadav et al. 2017; Saeid et al. 2018).

The soil exchangeable K, Ca, Na, and Mg in the immature pepper vine farm are shown in Table 7. Soil exchangeable K of inorganic fertilizers (F0) was significantly higher in 2017 and 2018. Only in the first year of assessment (2017), the treatments with fermented fruit juices (F3 and F4) showed comparable exchangeable K to that of the inorganic fertilizer (F0). In the second year, the organic amended treatments (F1, F2, F3, and F4) had lower effect on soil exchangeable K relative to F0 (Table 7). This significantly higher soil exchangeable K is related to the high K of the inorganic fertilizers (Yap 2012). However, it was found that there were substantial amounts of soil exchangeable K in the organic amended soils (Table 7) because of the presence of K-solubilizing microbes in the fermented juices (Yadav et al. 2017). Some examples of beneficial microorganisms in the fermented juices which can convert insoluble K to soluble K are Bacillus sp., Sporosarcina sp., and Aspergillus sp.

Table 7 Effects of o rganic amendments on soil potassium, calcium, sodium, and magnesium of an immature vine farm for 2 years of observation
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During the 2-year study (2017–2018), soil exchangeable Ca was significantly higher in F0, F2, and F4. Wong (1986) and Yap (2012) stated that in most chemical compound fertilizers, some essential macro-nutrients such as Ca are included in the formulation as supplementary nutrients for plants. This partly explains the higher soil exchangeable Ca in the NPK-fertilized plots (F0). It was also found that addition of biochar and compost into the soils contributed to higher soil exchangeable Ca (Table 7). Lehmann et al. (2006) found that amending soils with biochar improved exchangeable Ca and yield of several cash crops. They concluded that the increase in the exchangeable bases was due to ash of the biochar to release mineral nutrients such as Ca and K for crop use.

From 2017 to 2018, the NPK-fertilized plots (F0) showed higher soil Na availability compared with those under organic amendments. In year 2018, the soil exchangeable Na under F0 increased by 39%, suggesting that application of NPK inorganic fertilizer increased soil Na availability. Similarly, soil exchangeable Mg under F0 was significantly higher than those of F1, F2, F3, and F4. In 2018, the soil exchangeable Mg of F0 increased by 37%. The significant increase in soil exchangeable bases (Ca, K, Mg, and Na) with F0 is related to their contents in the inorganic NPK fertilizer used in this present study (Table 7).

These findings are consistent with that of Yap (2012) who also observed that patterns of the availability of Na were affected by continuous fertilizer use. Nevertheless, organic amendments can also provide soils and plants with sufficient nutrients such as P and K through degradation of organic materials in the fermented juices by beneficial microorganisms to release unavailable nutrients (Lee et al. 2008). Furthermore, the biochar-compost combination makes macro- and micro-nutrients more available to plants. Talaat et al. (2015) documented that improved productivity in crops with effective microorganism-inoculated composts compared with untreated composts was related to hastened decomposition of organic compounds into plant available nutrients.

Selected soil biological properties

Soil biological characteristics of a farm grown with immature vines for two assessment years under different soil amendments are presented in Table 8. In 2017, the soil respiration increased in the order of 5.06 < 5.37 < 6.30 < 7.70 < 8.77 μmolm−2 s−1 for F0 < F1 < F3 < F2 < F4, respectively (Table 7) and a similar trend occurred in 2018 as 4.91 < 5.13 < 5.37 < 6.82 < 8.07 μmolm−2 s−1 for F0 < F1 < F3 < F2 < F4, respectively. These results suggest that the soils with biochar, compost, and fermented fruit juice (FFJ) (F4) had the highest effect on soil respiration rate, whereas those with NPK chemical fertilizer only (F0) exhibited the lowest soil respiration rate. In a similar study by Zamora and Calub (2016), they also found that high soil respiration rate was related to stimulation microbial interaction in the soil or from the FFJ concoction. Fischer and Glaser (2012) also mentioned that composts with beneficial microbes increased soil respiration rate because of increased decomposing activities by beneficial microbes. Moreover, survival rate of the beneficial microbes was higher in the soils with biochar because microbes can inhabit the tiny perforations of biochars (Zimmermann 2008; Lawrinenko 2014). Mensah and Frimpong (2018) found that combined use of biochar and compost increased respiration rate in soils, indicating the positive interaction between these soil amendments and microbes.

Table 8 Effects of organic amendments on soil respiration, bacteria count, actinomycetes count, and fungi count of immature vine farm for 2 years of observation
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The findings on soil respiration in Table 8 were further supported by the results on soil microorganism count (bacteria, actinomycetes, and fungi). In 2017, bacteria count in 1 g of dry soil showed no significant differences among the organic treatments (F1, F2, F3, and F4), whereas the NPK-fertilized plots (F0) and the fermented juices only plots (F1 and F3) showed no significant differences. In 2018, the fermented juices, biochar, and compost treatments (F2 and F4) showed the highest bacteria count, followed by fermented juices only treatments (F1 and F3) and NPK inorganic fertilizer treatment (F0). Similar patterns manifested in the actinomycetes and fungi count where the soils with organic amendments especially those with biochar and compost were significantly higher than that of the NPK fertilizer soils. These findings corroborated with studies of Higa (2012) and Zamora and Calub (2016) who also observed that the use of soil organic amendments increased bacteria, actinomycetes, and fungi count by two to fourfold.

Population of the beneficial microorganisms of the fermented juices can be increased in soils mixed with compost and biochar that also has a large stable population of beneficial microorganisms, especially facultative anaerobic bacteria (Higa 2000; Doran and Zeiss 2000). Park and DuPonte (2008) added that repeated applications, especially during first cropping season, can markedly facilitate early establishment of the introduced beneficial microorganisms. Mensah and Frimpong (2018) stated that when these mixed cultures become established in soils together with biochar and compost, soil respiration rates increase significantly. If the microorganisms in the mixed culture can coexist and are physiologically compatible and mutually complementary, and if the initial inoculum density is sufficiently high, there is a high probability that these microorganisms will become established in soils and will be effective as an associative group, whereby such interactions would definitely increase carbon efflux from the soil (Lee at a., 2008; Partanen et al. 2010; Sharma et al. 2017).

Pepper morphological characteristics

In 2017, the organic fertilizer treatments (F1, F2, F3, and F4) showed significantly higher fruit spike length compared with that of the NPK-fertilized plot (F0) (Fig. 2). In 2018 however, the NPK-fertilized plot (F0) recorded the longest fruit spike length followed by the fermented plant juice treatment (F1), fermented juices with biochar and compost treatments (F2 and F4), and fermented fruit juice treatment only (F3). The results concurred with those of Wong (1986) and Yap (2012) who also suggested associated longer fruit spike length of immature pepper with level of primary nutrients in compound fertilizers.

Fig. 2
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Average length of fruit spike of immature pepper vines in 2017 and 2018 following application of organic fertilizers. Treatments are F0—compound fertilizer control, F1—fermented plant juice (FPJ), F2—fermented plant juice incorporated with biochar and compost (FPJBC), F3—fermented fruit juice (FFJ), and F4—fermented fruit juice incorporated with biochar and compost (FFJBC) (mean + S.D., n = 15). Means with same letter superscript within columns are not statistically different using Tukey’s at P > 0.05 probability level. Letters without prime represent year 2017 and single prime superscript represents year 2018

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According to Paulus (2011), NPK 15:15:15 is commonly used for young pepper vines especially during early fruit spike development in Sarawak, Malaysia. The immature pepper leaf area index (LAI) over two growing seasons is presented in Fig. 3. F1 recorded the highest LAI (4.92) in 2017 followed by F3 (4.66), F2 (4.63), F4 (4.58), and F0 (4.25). However, the effects of NPK fertilizer (F0) and soil organic amendments (F1, F2, F3, and F4) on LAI in 2018 were not significantly different (Fig. 3). It was observed that the LAI of F0 increased by 12% between 2017 and 2018 following NPK fertilization. On the other hand, between 2017 and 2018, F1, F2, F3, and F4 increased by 5%, 8%, 4%, and 9%, respectively following organic amendments. These findings are similar to those of Miller et al. (2013) who stated that 15:15:15 NPK fertilizer is effective in increasing LAI because it releases nutrients into the soil rapidly compared with organic fertilizers.

Fig. 3
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Average leaf area index (LAI) of immature pepper vines in 2017 and 2018 following application of organic fertilizers. Treatments are F0—compound fertilizer control, F1—fermented plant juice (FPJ), F2—fermented plant juice incorporated with biochar and compost (FPJBC), F3—fermented fruit juice (FFJ), and F4—fermented fruit juice incorporated with biochar and compost (FFJBC) (mean + S.D., n = 15). Means with same letter superscript within columns are not statistically different using Tukey’s at P > 0.05 probability level. Letters without prime represent year 2017 and single prime superscript represents year 2018

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Fresh berry yields of the immature pepper under different soil amendments are presented in Fig. 4. In 2017, the fresh berry yields were in the order of 7.59 < 7.67 < 7.99 < 8.06 < 8.44 kg for treatment F1 < F3 < F2 < F4 < F0, respectively. A similar trend was observed in 2018 during which the fresh berry yields were in the order of 7.10 < 7.24 < 8.04 < 8.52 < 8.82 kg for F1 < F3 < F2 < F4 < F0, respectively. Although F1 and F3 had longer fruit spikes, the immature vines grown on the soils with fermented juices alone did not significantly improve yield (Fig. 4). Paulus (2011) was of the opinion that this observation was due to the plants not receiving enough essential nutrients during fruiting and this led to fruit spikes having empty, smaller, and fewer berries. The NPK fertilizer plot (F0) showed the highest berry yield because of the response of the immature pepper vines to 15:15:15 NPK fertilizer (Yap 2012). In 2018, the yields of the organic amendment plots with biochar and compost (F2 and F4) were comparable to that of the NPK fertilizer plot (F0). In this study, it appears favorable that soil conditions are related to comparable yield increase of the immature vines under F2 and F4. Referring to the soil physical properties in Table 4, the soil bulk densities and porosities of F2 and F4 were good as those reported by McGrath and Henry (2016) that by incorporating biochar and compost into soils, soil aggregate stability increases most effectively in clayey and sandy soils. McGrath and Henry (2016) also mentioned that good soil structure or less compact soils are good for plant growth and yield. Besides, pH (5.0–5.5) of the soils with biochar and compost were near to pepper’s optimum pH requirement (Kumar and Swarupa 2017). Agegnehu et al. (2016) were of the opinion that biochar and compost application have liming effect because of their richness in Ca, Mg, Na, and K. These base cations are liberated from organic matter through mineralization. At the same time, soils with high CEC are more likely to develop high availability of K, Ca, Mg, Na, and other cations with less leaching of these cations (Fischer and Glaser 2012).

Fig. 4
figure 4

Average fresh berry yield of immature pepper vines in 2017 and 2018 following application of organic fertilizers. Treatments are F0—compound fertilizer control, F1—fermented plant juice (FPJ), F2—fermented plant juice incorporated with biochar and compost (FPJBC), F3—fermented fruit juice (FFJ), and F4—fermented fruit juice incorporated with biochar and compost (FFJBC) (mean + S.D., n = 15). Means with same letter superscript within columns are not statistically different using Tukey’s at P > 0.05 probability level. Letters without prime represent year 2017 and single prime superscript represents year 2018

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The use of biochar and compost significantly increased CEC of the soils (Table 5). The fermented fruit juices, biochar, and compost treatments contributed to positive changes in the soil physical, chemical, and biological properties. Four of the related soil property amendments that improved were TOC, available P, C/N ratio, and soil microorganism count (Table 6 and Table 8). These findings are in agreement with Zamora and Calub (2016) who also mentioned that application of fermented juices, biochar, and composts led to increased availability of nutrients through enhanced participation of microbial biomass, P, and K solubilizers, and associated soil enzymatic changes. These properties which were enhanced by F2 and F4 ultimately improved yield of the immature pepper under treatments (Fig. 4). The yield improvement observed could be attributed to improved nutrient and water retention capacity of the organic amendments. Thus, the increase in pepper yield due to organic amendments was in conformity with the expected soil improvements.

Economic analysis

Summary of the outcome on the economic assessment for introducing organic fertilizers in immature pepper cultivation is presented in Table 9. The estimated annual cost per hectare following the use of chemical fertilizer (F0) on immature pepper vines was RM8000, whereas by adopting organic amendments, the annual costs per hectare were reduced by F1—86%, F2—64%, F3—84%, and F4—63% (Table 9). Yield of the immature vines under NPK fertilization (F0) was 2.91 kg, followed by F4—2.81 kg, F2—2.65 kg, F3—2.39 kg, and F1—2.34 kg. In contrast, mature pepper vines ranging between 3 and 10 years have an average value of 3.60 kg/vine/year (Malaysian Pepper Board 2017). Based on the calculation of gross income (GI) and total production cost (TPC), the accumulated net cash flow (ANCF) of F0, F1, F2, F3, and F4 were RM94,324, RM94,098, RM103,663, RM72,192, and RM131,374, respectively. The cost of production for 1 kg of black pepper was highest in F0, followed by F4, F2, F3, and F1 with amounts of RM5.85, RM5.09, RM5.08, RM4.88, and RM4.87, respectively. With black pepper price at RM9.37 per kg and at a discount rate of 10%, the internal rate of return (IRR) of treatment F0, F1, F2, F3, and F4 were 17, 17, 19, 14, and 23%, respectively, whereas the net present value (NPV) were RM26,732, RM26,935, RM31,485, RM14,215, and RM48,575, respectively. The highest benefit-cost ratio was observed in soils amended with FPJ, biochar, and compost with a ratio of 1.4, followed by F2 (1.3), F1 (1.3), F0 (1.2), and F3 (1.2). The year of payback for the treatments under NPK fertilization (F0), FPJ combined with biochar and compost (F2), and FFJ plus biochar and compost (F3) will be in the fifth year, whereas those of FPJ and FFJ only will be in the sixth year.

Table 9 Summary of a 10-year economic analysis on immature pepper vines following different organic fertilizer applications based on 2018 fresh berry yield data
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Positive values on NPV and an almost similar BCR for F0–F4 treatments indicate that practicing organic farming in immature pepper vine cultivation is comparable to the existing practice (chemical fertilization). Paulus and Anyi (2011) stated that because immature vines do not need substantial amount of chemical fertilizers as required at mature stage, lower investment on expensive chemical farming input means income sustainability for farmers. At the same time, the organic fertilizer application of using fermented juices only or fermented juices with biochar and compost also will yield good economic return for farmers in the first 3 years of the immature vine cultivation. This is supported by a study done by Paulus and Anyi (2011) who also stated that although pepper yield was lower in organic farms that were not subjected to chemical fertilization, on the production cost per yield basis, it provides higher or comparable benefit-cost ratio compared with conventional practice.

Conclusion

Application of fermented juices, biochar, and compost can positively improve soil bulk density, soil porosity, pH, CEC, TOC, C/N ratio, available P, and exchangeable Ca. Furthermore, the treatments can improve soil respiration and soil microorganism count (bacteria, actinomycetes, and fungi). Although the fermented juices only, or fermented juices with biochar, and compost exhibited lower effect on LAI and fruit spike length, their effects on fresh berry yield were comparable to that of NPK fertilizer only. The economic viability study suggests that the organic approach of using fermented juices only, or fermented juices with biochar, and compost was comparable to the existing NPK fertilization program. Therefore, application of organic fertilizers in black pepper cultivation on soils grown with immature vines is essential, practical, and economically viable.