Yield, nutrient and carrying capacity of aerial cassava as influenced by organic fertilizers and defoliation on drylands in lampung, Indonesia

Anhar Faisal Fanani^2,3, Asnath Maria Fuah, Komang Gede Wiryawan¹, Salundik and Sri Rahayu

Department of Animal Production and Technology, Faculty of Animal Science, Bogor Agricultural University. Jl. Agatis, Kampus IPB Darmaga, Bogor 16680, Indonesia
asnath.fuah@gmail.com
¹ Department of Nutrition and Feed Technology, Faculty of Animal Science, Bogor Agricultural University, Jl. Agatis, Kampus IPB Darmaga, Bogor 16680, Indonesia
² Program Study of Animal Science, Faculty of Agriculture, Fisheries and Animal Science, Nahdlatul Ulama University of Lampung, North Lampung 34192, Indonesia
³ Program Study of Animal Science, Faculty of Agriculture, Mulawarman University, Jl. Pasir Balengkong, Kampus Gunung Kelua, Samarinda 75123, Indonesia

Abstract

The aerial part of the cassava plant (leaves and petioles) has value as a protein source in livestock feed. This study aimed to determine the effect of organic fertilizers on the nutrient content this foliage and the effect of defoliation on the yield of cassava roots at the time of harvest. The study was arranged in a completely randomized design with 2 factors and six replications. The factors was source of organic fertilizer: CTL (non organic fertilizer); GM: goat manure at 2.5 tonne/ha; VC: vermicompost. The second factor was defoliation (DF) or none (NDF). The variables measured were: nutrients, aerial biomass, carrying capacity, yield of roots.

There was no interaction between organic fertilizer and defoliation on nutrient content. Organic fertilizer increased yield of foliage and carrying capacity. Defoliation decreased the yield of roots. It was concluded that the use of organic fertilizer with defoliation resulted in better nutrition as feed for goats and increased carrying capacity, with no reduction in roots at harvest.

Key words: aerial harvest, HCN, nutrients composition, vermicompost

Introduction

Most of the population living in rural areas in the world earn their livelihoods from mixed farming systems. In Indonesia, 43.58% of the population are working in the agricultural sector (Statistic Indonesia 2021). Small-scale agricultural management plays an important role in developing villages and supporting local food by integrating agricultural and livestock components. The management of livestock in the village generally utilizes by-products from agricultural crop commodities as animal feed, especially cassava. Like other tropical countries that cultivate cassava, Indonesia is one of the major cassava-producing countries with production reaching 19.34 million tonnes per year with the largest production being in Lampung (Ministry of Agriculture 2020). However, in general, farmers only use plant residues at the top, namely the stem on the lowest leaf or about 50 cm from the top as feed. In the meantime, the need for seeds for the next planting period is about 15% of the previous crop, leaving a lot of stem waste and not being handled as an effort to return organic matter to the soil. The ratio of the top of cassava plants to roots at harvest is 2:3 (Munyahali et al 2017).

Cassava cultivation is generally carried out on dry land (Hafif 2016). However, the use of dry land as marginal land has problems with low soil fertility due to chemical barriers (Sardiana et al 2017). This soil has a low pH and organic matter content and low cation exchange capacity which further limits crop yields (Maswar and Soelaeman 2016; Iqbal 2012; Anda and Kurnia 2010; Haridasan 2008). Inorganic fertilizers are more commonly used to maintain agricultural production (Aainaa et al 2015). The use of inorganic fertilizers has a negative impact on the environment if it is poorly managed. According to Omidire et al (2015), inorganic fertilizers release high nutrients needed by plants and do not go through a decomposition process. The combination of inorganic and organic fertilizers on plants has been reported to have a positive effect on growth, productivity and yield quality (Sarhan et al 2011; Anjanappa et al 2012). Reports (Prabowo et al 2015) imdivate that cassava farmers in production areas sometimes do not apply the use of organic fertilizers.

Many studies have reported the use of various organic fertilizers on land to increase yields such as liquid fertilizers, manure fertilizers, biological fertilizers and vermicompost (Esmaielpour et al 2018; Filho et al 2018; Han et al 2016). However, there have not been many tests using a combination of fertilizers with the aim of maximizing the aerial yield in the form of cassava foliage as a means to improve livestock carrying capacity.

Therefore, this experiment was carried out to evaluate: (i) the effect of adding organic fertilizer on the forage quality, production and carrying capacity of livestock from the aerial part of cassava plants; and (ii) effect of defoliation tield of total biomass and yield of roots at harvest.

Materials and Methods

Study area

Figure 1. Research location in Sidodadi Village, Pekalongan District, East Lampung Regency, Lampung Province, Indonesia. The coordinates (5°05'23.0"S 105°23'21.5"E)

Figure 2. Rainfall during the study

This study was carried out on dry land from March to November 2021 in Sidodadi Village, Pekalongan District, East Lampung Regency, Lampung Province (Figure 1). The research site is located at an altitude of 55 m above sea level. The soil has a pH of 4.48 and has a dusty clay texture. Soil chemical content in the form of total N, P, K, C-organic, and cation exchange capacity was 0.173%, 11.87 mg 100g^-1, 1.86 mg 100g ^-1, 1.16%, and 5.28 me 100g^-1, respectively. Rainfall data in the low category <100mm to high>300 mm are presented in Figure 2 (BMKG 2021).

Design and treatment

The experimental design used a completely randomized design with a factorial arrangement that was repeated six times. The first factor was the effect of organic fertilizer which consisted of 3 types, namely without organic fertilizer (CTL); 2.5 tonnes of DM/ha of goat manure (GM); and 2.5 tonnes/ha as DM of vermicompost manure (VM). The second factor was the amount of aerial defoliation of cassava plants, namely non-defoliation (NDF) and defoliation (DF).

Five ha of land was divided according to the number of experimental plots. Soil preparation was carried out before planting. Inorganic fertilizers were applied to all treatments and nursings in accordance with the recommendations of ILETRI (2021). Application of organic fertilizer was done before planting. Fertilizer came from fermented fresh goat manure, while vermicompost came from goat manure media which was previously refined and decomposed using african night crawler earthworms (Eudrilus eugeniae). The C-organic content, total N, P, K, and C/N ratio in organic fertilizers are presented in Table 1. The cassava variety ad a low cyanide content that as accepted by the flour industry. The plant stems for seed were obtained from farmers around the test site. Spacing of cassava was at 80 x 80 cm in monoculture (15,625 cuttings/ha).

Data collection and crop harvest

Aerial yield is all above-ground biomass, including stems and leaves (twigs with leaves). The cutting is done 40 cm above the soil surface. Sampling of each experimental plot was carried out in an area of ​​1x1 m (four plants). Unused material is the part of the stem in the ground attached to the cassava roots tuber up to 40 cm cutting above the ground or the local term is called the hump. In the treatment with defoliation, measurements are carried out twice, namely 4 months after planting and 8 months after planting (when harvesting the roots). Analysis for crude protein (CP), crude fiber, crude fat, ash, nitrogen free extract (NFE) are taken for the stems and leaves that have been composited and analyzed proximately according to the AOAC method (2005). Hydrogen cyanide (HCN) analysis was carried out on all treatments at harvesting the roots. The HCN content is analyzed following the AOAC method (1990). Calculation of the total digestible nutrient content (TDN) based on the results of the proximate analysis follows the method of Moran (2005). Starch testing is based on the method of Sudaryono and Supeno (2017). The carrying capacity is calculated based on the production of dry matter, crude protein and TDN following the method of Kusmiyati et al (2019). The approach in determining the carrying capacity based on the needs used for one livestock unit (an steer of 450 kg and an ADG of 0.5 kg/day; Kearl 1982).

Data analysis

The data were analyzed using analysis of variance with SPSS 16 software. Duncan's multiple range test was performed if there were significant differences (Steel et al 1997).

Results and discussion

Chemical content of cassava plants

There was no interaction between organic fertilizer application and defoliation on chemical composition (Table 2). The application of organic fertilizers had no effect on the nutrient content of the aerial plants except for DM. Cassava plants with vermicompost without defoliation produced the highest DM (25.26 g) (Table 2). In the study, it was found that harvesting carried out twice (defoliation) resulted in lower DM compared to aerial harvest when harvesting the main crop (non-defoliated) which was influenced by the age of the plant. Defoliation treatment caused rejuvenation in cassava plants. High DM levels in the non-defoliating treatment were related to the length of photosynthesis, namely the period of the plant filling phase (Sriagtula et al 2021). In non-defoliation, aerial harvest was at the age of cassava plants 8 months after planting (BST), so that photosynthetic activity was longer than in the defoliation treatment (4 BST and 8 BST cutting). This result is in line with (Koca and Erekul 2016) where DM accumulation will increased from the emergence of shoots to the maturity stage. Organic fertilizers affected the DM content of all aerial plants. The application of vermicompost resulted in higher DM compared to others, but the trend of increasing CP was not found in the application of organic fertilizer.

The CP content of all organic fertilizers treatments harvested with the highest defoliation (15.11 g 100g^-1 DM) and decreased (p<0.01) without defoliation (10.4 g 100g^-1 DM). In this study, differences in CP content due to the number of cuts were also observed by Hue et al (2012). It could be that the increase in CP content was related to rejuvenation in the defoliation treatment, resulting in more young leaf production. Cassava plants with increasing age would experience leaf loss as experienced in the non-defoliation treatment so that it affected the leaf: stem ratio (Table 4), while the highest CP content in the cassava plant was in the leaves. The results of this study's CP were lower than Khang et al (2005) the CP content of cassava leaves was 18.33 g 100g^-1 DM. In general, CP is a chemical component of forage that moves downward as a vegetative to the generative stage with increasing plant age. In addition, the crude fiber content increased over the same time period.

The decrease in crude fiber content occurred in all applications of organic fertilizer with defoliation. The crude fiber content of all aerial cassava plants harvested by defoliation resulted in the lowest crude fiber (32.4 g 100g^-1 DM). This can be explained that cassava plants that undergo rejuvenation by defoliation also reduce crude fiber. The high proportion of stems (Table 4) resulted in higher fiber content in non-defoliated cassava plants so that defoliated crude fiber could decrease up to 19.8%. Sriagtula et al (2017) stated that crude fiber was affected by the accumulation of sugar in the stem with increasing time. The crude fiber content in forage also affects the quality of animal feed. Crude fiber can be a measure of digestibility and is often associated with the negative contribution of livestock farming to global warming due to enteric methane (CH4) production (Archimède et al 2011; Berça et al 2019).

The aerial ash content of plants in all organic fertilizer applications increased (p<0.01) with defoliation treatment, due to the dynamics of mineral nutrition in cassava plants. The ash content of all non-defoliated aerial harvests decreased by 28% with no delay in cassava maturity. During the rejuvenation phase with defoliation, the ash content, especially Ca and P increased for stem and leaf growth, then with increasing time it would be translocated to the tuber part of the plant. Gracia and Grusak (2015) stated that micronutrients from leaves and stems will be mobilized to developing plant parts such as tubers. Plants with increasing age of maturity will increase starch so that it affects the percentage of ash (Sriagtula et al 2017; Rosser 2013). The effect of maturity age also affects higher crude fat. This increase is of course also influenced by the accumulation of starch that begins to be stored in cassava tubers. Wang et al (2018) explained that lipids are part of starch in the form of free fatty acids. The decrease in crude fiber and increase in CP in the defoliation treatment affected TDN numerically.

Production characteristics

The ability of the land to provide animal feed is a farmer’s goal in choosing a cultivation system (alternative feed) because the livestock that is raised must be adjusted to the production cycle with the carrying capacity of the land owned to produce the number of kilos of aerial crop production. In this study, the use of organic fertilizer applied to cassava plants with defoliation gave better aerial quality (Table 2). In the test area, defoliation treatment would maintain more leaves that fall due to the maturity of cassava plants. Organic fertilization (eg vermicompost) will add nutrients that tend to increase new leaves as a result of the production of new cells.

The characteristics of aerial cassava production are presented in Table 3. There was no interaction between organic fertilizer and defoliation at harvest on production characteristics in this study. Aerial biomass, CP production, and TDN production increased significantly with differences in the application of organic fertilizer at harvest. Aerial biomass production increased 18.4% with the addition of vermicompost and defoliation of cassava plants. This increase in aerial feed biomass is explained by accelerated plant growth due to fertilization, resulting in increased leaf production (Venturini et al 2017; Schmitz et al 2020). In plants, the addition of nutrients increases the nutrient content of forages, especially the content of CP, because plants absorb N and combine it with sugars, producing amino acids to form proteins (Andrews et al 2013). Several reports also found that there was an increase in forage production by adding organic fertilizers to feed crops (Kumar et al 2017; Yoottasanong et al 2015). McRoberts et al (2018) added that providing nutrients for plants with the use of fertilizers is a strategy to increase plant mass.

Increased CP production (p<0.01) with defoliation in all treatments of organic fertilizers was due to the support of the N content of organic fertilizers. The lowest CP production value was 0.39 tons DM ha ^-1 and the highest was 0.70 tons DM ha^-1. This higher yield is in line with that reported (Vivasane et al 2017). The nutritional value of forage can be increased by adding N (Lee et al 2017). The nitrogen content of vermicompost used in this study was 1.61%. Adding 2.5 tons ha^-1 DM vermicompost indicated the addition of 40.25 kg ha ^-1 nitrogen to the soil and was correlated with increasing CP production by 16.7%. This is because N is a limiting element for plants (Berça et al 2019), and there is a positive relationship between growth and nutrient quality (Mazzetto et al 2016). The lower C/N ratio of vermicompost compared to manure makes it better for planting.

The carrying capacity of DM, carrying capacity of CP, and carrying capacity of TDN (p<0.01) were influenced by the presence of defoliation and supported by organic fertilizer. However, the total available DM production that could accommodate livestock was lower than the capacity based on CP. The CP carrying capacity of all organic fertilizer applications was the highest (4.08 AU ha^-1). In the defoliation treatment, the carrying capacity of CP was numerically 80% higher with 2.5 ton ha ^-1 vermicompost treatment than the non-defoliated and not given organic fertilizer. Meanwhile, the effect of defoliation on various organic fertilizer treatments did not affect the yield of fresh tubers obtained (Table 4).

The application of organic fertilizers and defoliation resulted in a higher capacity of DM carrying capacity. The carrying capacity of this study based on DM was 1.57-1.87 AU ha^-1 during the growing season. The results of the forage carrying capacity study reported in the lowland swamps of South Kalimantan was 2.91 AU ha^-1 year^-1 (Rostini et al 2014); lowland swamps of South Sumatera 2.04-2.61 AU ha ^-1 year^-1 (Muhakka et al 2019). Meanwhile, the grasslands of Timor Tengah Selatan Regency are 0.63 AU ha^-1 year^-1 (Se’u et al 2015). However, it is not justified to compare the carrying capacity of forages in nature with the results of this study, because the yield of cassava residues obtained is a one-time planting period of less than a year.

The quality and aerial palatability of cassava plants are quite good for small ruminants such as goats and sheep which can be fed alone or with other feed ingredients. Jiwuba (2020) reported that consumption of cassava leaves as much as 15% of DM rations was able to produce a weight gain of 85.26 g day^-1 in goats. DM intake and weight gain of sheep fed with cassava leaf alone were 544 g day^-1 and 41.6 g day^-1, respectively (Fasae et al 2012). Recommendations for DM, CP, and TDN requirements are 730 g DM day^-1, 71 g CP day ^-1, and 460 g TDN day^-1, respectively, for goats weighing 25 kg and gaining bodyweight of 75 g day^-1 (Kearl 1982). Based on the recommendations for the intake of DM, CP, and TDN, the remaining cassava plants with the application of vermicompost and defoliation can accommodate 26 goats based on DM, 41 goats based on CP, and 25 goats based on TDN.

Aerial structure of cassava plant

In the application of vermicompost and compost, the yield of cassava leaves (p<0.01) was higher in the presence of defoliation, but without organic fertilizer and without defoliation the yield of leaves was lower (Figure 3). The higher leaf yield in the defoliation treatment also resonated to increase the leaf/stem ratio of aerial cassava plants compared to non-defoliation, which certainly affected aerial CP because the highest protein content was located in the leaves. Tung et al (2001) stated that intensive cutting of cassava plants resulted in high CP production. The proportion of leaves with defoliation in this study was found to be 53% from aerial cassava plants which increased levels of CP 15.11 g 100g ^-1 DM from non-defoliated 10.40 g 100 g^-1 DM. The increase in CP production is certainly also influenced by the chemical content of aerial cassava.

Figure 3. Effect of organic fertilizer and defoliation on cassava leaves CTL: non-organic fertilizer; GM: goat manure; VC: vermicompost; ND: non-defoliation; D: defoliation

Higher stems (p<0.01) in the treatment without defoliation would affect the lower leaf/stem ratio compared to the defoliation treatment. Cassava plants in general will shed old leaves as the plant ages, causing the proportion of cassava stems to be high. However, the age of cassava leaves varies, depending on the genotype (Phosaengsri et al 2019). This is what causes many cassava stems to be not utilized in the field and farmers are not given special handling to return crop residues to the ground. Defoliation treatment was able to reduce stems by 33.2% and increase leaf yield 121.4% higher than non-defoliated. According to Khang et al (2005), cutting will affect the growth of new leaves.

Main production and content of HCN

The effect of the main yield of cassava and HCN content is presented in Figure 5. There was no interaction between organic fertilizer application and defoliation on main yield and HCN content in this study, with defoliation affecting aerial HCN of cassava (p<0.01). A large difference in HCN content with different harvest amounts was reported in the study of Hue et al (2012). The current experiment indicated that the HCN response pattern was similar to aerial harvests with defoliation, and the addition of organic fertilizers appeared to have an effect. The HCN content depends on the variety, plant genetics and soil fertilization (Nduwumuremyi et al 2017). Limiting substances such as HCN are toxic and can cause death. Therefore, efforts are needed to reduce it, for example, by way of drying or silage.

The production of tubers (Figure 4) and the number of tubers planted (Table 4) were not affected by the application of organic fertilizers or defoliation (p>0.05). This result is similar to the report of Munyahali et al (2017) that pruning twice did not affect tuber production. However, defoliation reduced the starch content of harvested tubers (p<0.05). The decrease in the estimated starch content in tubers with defoliation was 3.8%, and this is still profitable with the results of increasing the aerial nutrients obtained and not disturbing the production of fresh tubers. The cassava varieties used in this study were short-lived. Starch content can be increased by increasing the age of harvest. Photosynthetic yields are divided for new leaf growth and into tubers where the starch content becomes lower upon defoliation. The balance of leaves and roots as storage is very important to maximize productivity yields (Lemoine et al 2013; Kawano 1990). Leaves have an important function in photosynthesis, carbon assimilation and growth, and have simultaneous leaf and root growth as reserves (El-Sharkawy 2004). The right time to defoliate after the rain is expected to have a beneficial effect on the growth of new shoots of cassava plants. However, the addition of aerial harvesting of cassava by defoliation in Indonesia is not yet common.

Figure 4. Effect of organic fertilizer and defoliation on tuber production. CTL: non-organic fertilizer; GM: goat manure; VC: vermicompost; ND: non-defoliation; D: defoliation	Figure 5. Effect of organic fertilizer and defoliation on HCN content. CTL: non-organic fertilizer; GM: goat manure; VC: vermicompost; ND: non-defoliation; D: defoliation

Conclusion

• Increasing aerial production of cassava plants by improving foliage composition using a defoliation harvesting strategy supported by vermicompost fertilization resulted in better nutrition and carrying capacity.
  
  
• Could be developed for animal feed needs and still have economic value when harvesting tubers.

Acknowledgment

I would like to extend my gratitude to the Ministry of Education, Culture, Research, and Technology of the Republic of Indonesia for educational assistance through the BPPDN scholarship. My appreciation also goes to the Deputy for Strengthening Research and Development, Ministry of Research and Technology/National Research and Innovation Agency for financial support through research grants No. 1981/IT3.L1/PN/2021.

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