Trees and Soil Management Impacts on Soil Nutrient and Coffee Production in Coffee-Based Agroforestry

Trees and soil management practices (i.e., pruning and fertilization) are essential in maintaining the soil fertility and coffee yield sustainability in coffee agroforestry systems. This study aimed to evaluate the impact of trees and soil management practices on the soil nutrient status within coffee-based agroforestry systems. The research was conducted in coffee agroforestry systems within Universitas Brawijaya Forest (UB Forest) from January to July 2023. The experiment was performed using a factorial randomized block design with three factors, including: 1) pruning of coffee (T1: pruned coffee, T2: unpruned coffee), 2) Fertilizer type (O: organic fertilizer, A: inorganic fertilizer, M:50% organic + 50% inorganic), and 3) Fertilizer dosage (D1: Farmer‘s dose, D2: recommended doses from the Indonesian Coffee and Cacao Research Institute (ICCRI), D3: Dosage from nutrient replacement), totaling 18 treatments with four replications of each. The soil sample was collected at topsoil (20 cm soil depth) around 50 cm from the coffee stem at the beginning of the research and six months after fertilization. The study revealed that tree management affected (p>0.05) soil nutrient status (i.e., soil total N and available P), where pruned coffee management increased soil nutrient status by 2.02 to 4.53 times compared to the unpruned coffee plot. Types and doses of fertilizer significantly affected soil pH (P < 0.05), where the application of organic fertilizer with the recommended dose (OD2) had the highest soil pH. The correlation analysis showed that soil nutrients correlated to coffee yield. The principal component analysis shows that pruned coffee combined with mixed fertilizer at the farmer‘s dose (T1MD1) is closely related to coffee production.


Introduction
Coffee plantation has significant value from an economic and ecological perspective.The high demand for coffee has encouraged increased coffee cultivation, including in Indonesia.Malang Regency is one of the three largest coffee producers in East Java province, Indonesia [1].Coffee is one of the plantation commodities that has an essential impact on Indonesia's foreign exchange from the non-oil and gas sector.1,238,596 hectares of coffee land produces 717.962 tons.year-1coffee beans [2].Coffee 1299 (2024) 012003 IOP Publishing doi:10.1088/1755-1315/1299/1/012003 2 cultivation using agroforestry is common because coffee plants need shading to grow and produce coffee beans.Agroforestry positively impacts the environment by maintaining soil fertility, carbon stocks, biodiversity, regional hydrological functions, and reducing greenhouse gas emissions [3].The benefits of coffee-based agroforestry have caused coffee-based agroforestry to be widely implemented in Indonesia.
UB Forest, with an area of around 554 hectares, is an education forest that applies an agroforestry system with coffee as the main cash crop, pine, silk trees, and mahogany as the shade trees [4].However, the management applied in coffee-based agroforestry is different for each farmer.Farmers manage coffee in UB Forest with a relatively small land area, an average of 0.7 hectares [5].The size of the coffee site influences agricultural business; the smaller the land use, the more inefficient the farming, and will impact the farmer's income [6].The small land area causes farmers to decide on land management based on their income, especially the management of coffee trees and soil.Differences in tree and soil management (i.e.fertilization and pruning) potentially affect coffee yield and soil fertility [7].
Pruning is a vital coffee plant management activity to grow well and get optimal yields.Pruning aims to remove diseased branches and unproductive branches and also adjust the height of the plants to make it easier for farmers to harvest [8] and maintain coffee productivity [8]; [9].Previous studies explained that the practice of pruning coffee plants has higher productivity than those that are not pruned [10].Regular pruning management will lead to gains in coffee yield.
Fertilization is one of the soil management practices that aim to maintain the availability of nutrients in the soil for supporting plant growth and production.Adding fertilizer (both organic and inorganic) at appropriate dosage significantly impacts soil macro and micronutrients [11], as well as coffee yield.Previous research reported that applying organic fertilizer increased soil organic matter, water-holding capacity, and the number of microbes in the soil [12]; [13].In addition, organic fertilization also increased soil pH and P content, reducing the amount of Al and Fe content in the soil [14]; [15] as well as increasing the growth of coffee plants [16].Further, inorganic fertilizers also increase soil availability of nutrients that plants can absorb directly [17].Previous studies reported that organic fertilizer significantly affected Arabica coffee production [18].
Combining appropriate tree and soil management will impact sustainable soil fertility and coffee productivity.Another study explains that pruning and fertilization treatments increase crop production [19].Nutrients are one of the soil health indicators and are closely related to sustainable coffee production.The imbalance of nutrients in the soil is one of the factors in reducing soil fertility, which results in decreasing yield.On the other hand, the balance of available nutrients in the soil is also supported by the physical and biological properties of the soil.Reducing the nutrient content in the soil, either due to leaching or erosion, will impact the growth and yield of coffee production [20].In addition, land-use systems, including their management, controlled soil nutrient storage [21].Thus, maintaining nutrient balance and availability through land management practices is crucial for the sustainability of coffee agroforestry systems.However, the understanding of the effect of combined management (i.e., pruning, types, and doses of fertilizer) applied on soil nutrient and their relationship to coffee production has yet to be reported.Therefore, this study aims to evaluate the impact of coffee pruning and fertilizer application on soil nutrients in a coffee agroforestry system.

Study site characteristics
The research area is in UB Forest that located in Sumbersari, Tawang Argo Village, Karangploso District, Malang Regency.Topographically, UB Forest is 1,200 meters above sea level (m asl) with slopes ranging from 15% to 45%.UB Forest is geographically located at 112°34'37" E and 7°49'36" N [22] (Figure 1).The average annual rainfall at the study site is 2,107 mm.year -1 , with a monthly average of 204.75 mm.month -1 .Agroforestry is a system applied at the study site, with arabica coffee plants (Coffea arabica) as the main crop and pine trees (Pinus merkusii) as shade plants.

Research design
This study was conducted by using a factorial randomized block design with three factors, namely: 1) pruning of coffee plants (T1: pruned coffee, T2: unpruned coffee), 2) type of fertilizer (O: organic fertilizer, A: inorganic fertilizer, M: 50% organic + 50% inorganic), and 3) fertilizer dose (D1: farmer's dose, D2: dose from recommended doses from the Indonesian Coffee and Cacao Research Institute (ICCRI), D3: dose from nutrient replacement due to the coffee bean harvest) [22] (Table 1).The research had 18 treatments with four replications, resulting in 72 experimental plots.This research was conducted on coffee plants that were 8-10 years old.The research plots were selected based on differences in coffee plant management (pruned and unpruned coffee).The plot size is 4 × 6 meters for each treatment in each replication (Figure 2).Fertilization was applied by putting it into a 10 cm fertilizer hole around 50 cm from the coffee stem

Soil sample collection
Soil samples were collected at three different points around the coffee trees at 30 cm from the stem.Soil sampling was conducted at initial field study and six months after fertilizer application [23] (Figure 3).The soil samples are prepared in air-dried for a week and ground until pass a 2 mm sieve.Air-dried soil samples that passed through a 0.05 mm sieve were used for soil total N and available P, while soil that passed through a 2 mm sieve was used to determine soil pH.

Soil chemical analysis
Soil pH, soil total N (TN), and Available P (AP) were measured to determine the effect of treatment on soil nutrients.Soil chemical analysis is measured using laboratory analysis standards procedure [24].0.5 grams of air-dried soil samples that passed through a 0.05 mm sieve were used for total soil N analysis using the Kjeldahl method, and 2 grams of air-dried soil samples were used for P analysis available using the Bray method.Ten grams of soil was mixed in 10 ml of distilled water and then used to measure soil pH using a glass electrode.

Coffee production analysis
Coffee beans were harvested manually by picking ripe beans in all experimental plots, then composited and counting the number of beans in each treatment combination.Coffee bean yield was calculated using the formula: Coffee yield (kg.ha -1 )= Mean of Coffee bean of each tree x coffee tree population on ha -1 1000

Statistical analysis
The data obtained was tested for normality using the Shapiro-Wilk's Test.Normally distributed data was analyzed using factorial Analysis of Variance (ANOVA) at the 5% level, followed by the Fisher's Least Significant Difference (LSD) post-hoc test to determine the differences between treatments.Correlation tests were conducted to explain the relationship between parameters and coffee production.Principal Component Analysis (PCA) defines the relationship between management and the parameters being tested.All statistical analysis was conducted by using R studio.

Arabica Coffee Production
The results showed that the yield on pruned coffee management (T1), with an average of 666.4 kg.ha-1, was higher than unpruned coffee management (T2), with an average production of 212.9 kg.ha.-1.
Removing unproductive branches and preparing fruit-bearing branches to focus the transport of nutrients to productive branches are the main focus of coffee pruning management [25].This pruning can increase coffee production on pruned coffee land.Fertilizer application can speed up the availability of nutrients, causing the available nutrients to be used more quickly by coffee plants.Previous studies support our findings that the addition of fertilizer has a significant effect on Arabica coffee yield [26].
The preliminary measurement showed that total N in the research plot was ranged from 0.51 -0.63%, whereas in the end of research, the soil total N was slightly decreased (ranged from 0.37 -0.62%).Tree management gave a significant effect (p<0.05) on the total nitrogen (TN), where soil TN was higher in the pruned coffee plot than those in the un-pruned coffee plot (Figure 4a).The increase in TN was due to the addition of nutrients because the pruned coffee (T1) contains plant residues from pruning, thereby increasing the total N content in the soil.Litter and pruning residues slowly decompose, improving soil fertility [27].

Effect of pruning and fertilization on N-total in soil
Soil organic matter is one source of TN in the soil.Thus, The high total N in the soil is likely caused by a high soil organic matter content.Coffee-based agroforestry systems within UB Forest tend to have a high soil organic matter [21].Soil management practices such as addition of organic fertilizer can increase TN up to 0.25% [28] [29].Organic matter affects physical, chemical, and biological properties such as soil pH, CEC, base saturation, and exchangeable cations, so the increasing organic matter in the soil can impact the soil [30].

Effect of pruning and fertilization on available-P
Prior to fertilizer application, the soil available P in the site was ranged from 10.33 -21.55 ppm.The results showed that soil available P after 6 months fertilization ranged from 7.60 -22.95 ppm.Tree management gave a significant effect (p<0.05) on available P (AP; Figure 4b).Pruned coffee management (T1) had higher soil AP than unpruned coffee management (T2).Together with fertilization practices, the amount of organic matter from pruning added to the soil is expected to be the factor affecting this result.Organic materials addition (e.g., manure and plant residues) has been reported to increase the AP [31].P is the essential nutrient that plays a role in the growth of roots, fruit, seeds development, and disease resistance [32].
The study could not detect significant differences among different types and doses of fertilizer on soil AP.These were probably due to soil in the plot research being formed by the andic material, with a large capacity for binding P and resulting the low available P [21].In addition, the insignificant difference in soil AP among fertilizer treatments was probably due to the high uptake of P by coffee plants.The previous study reported that the P content in the leaf of Arabica coffee plants from different organic fertilizer applications ranged from 0.49 g.100g-1 to 0.62 g.100g-1 [33].

Effect of pruning and fertilization on soil pH
Soil pH is one indicator for determining nutrient availability in the soil.The initial soil pH was 5.54 -5.71 and it was categorized as slightly acid.While, after six months fertilizer application, the soil pH ranged from 5.42 -5.85.Fertilizer application with different types and doses were significantly affected to soil pH (p<0.05) (Figure 4c).Organic fertilizer with a recommended dose (OD2) had higher soil pH than the other combination treatments.Our finding corresponds to previous research that organic matter increased soil pH [34].The increase soil pH is due to base cations that release through the decomposition [35].More base cations release into the soil colloids, give a high base accumulation, increasing pH.The degree of soil acidity due to the application of organic material depends on the maturity level of the organic material, the shelf life of the organic material, and the type of soil [36].

The relationship between the effect of total-N, available-P, and soil pH on coffee production
The results of the correlation analysis showed that TN, AP, and pH were positively correlated to the yield of coffee (Table 2).The correlation coefficients were 0.705, 0.709, and 0.489, respectively.The results indicate that coffee yield increases with increasing soil fertility conditions.This finding aligns with previous research that increasing soil fertility can increase the production and quality of physical coffee beans [37]; [38].
Microorganisms use soil N to decompose compounds or materials in the soil.The mineralization rate is determined by the quality of organic materials, one of which is nitrogen content [39].The higher nitrogen content, the faster the organic material will decompose because microorganisms need nitrogen as a component of cell [40].The amount of available N in the soil is also closely related to the organic matter content of the soil, especially the degree of decomposition [41].Nitrogen is needed in the photosynthesis process [42].Sufficient N in the soil can provide better growth and production for coffee plants.
Soil phosphorus (P) supports the growth and yield of coffee plants, and P in plants will affect the absorption of other essential nutrients that support the growth and development of coffee plants.Malhotra et al. [43] stated that P deficiency can reduce crop production by 30-40%.P is a nutrient element that plants need.P is absorbed by plants as inorganic phosphate from the soil; after being absorbed by plants, inorganic phosphorus changes into organic forms such as adenosine triphosphate (ATP) and adenosine diphosphate, which are used as energy carriers [44].ATP and ADP play an essential role in photosynthesis, so an increase in P in the soil can affect the production of coffee plants.
While the pH in the soil influences soil fertility for plant survival, pH has an optimum limit for growth and good yields for coffee plants.The pH range of 5.5-6.5 is optimal for plant growth as the availability of nutrients is optimal.The ideal soil acidity (pH) level for growing coffee plants ranges from 5.3 to 6.5 [45] [46].
PCA analysis showed that pruning management is closely related to coffee production.Pruning will help transport nutrients to productive branches so that seed filling.Using fertilization doses with the optimal type has had a good impact.This research aligns with previous research that application organic fertilizer with inorganic fertilizer works synergistically; applying organic fertilizer increases the effectiveness of using inorganic fertilizer [47].
PCA results revealed that all soil chemical properties tested were related to coffee production (Figure 5).This condition indicates that soil fertility status is associated with forming and filling coffee beans that can run optimally.The management of pruned coffee with the application of farmer's doses of mixed fertilizer (T1MD1) has a close relationship with coffee production.

Conclusion
Pruning management practices in coffee plants influenced TN and AP.The pruning treatment increased the nutrient content by 2.02 to 4.53 times compared to the non-pruning treatment.Application of different types and doses of fertilizer had a significant effect (p>0.05) on soil pH in all treatments except for organic fertilizer at farmer's doses.Adding organic fertilizer at the dosage recommended by the Indonesian Coffee and Cacao Research Institute gave a higher soil pH than other combination treatments.Further, soil pH, and soil nutrients (i.e., TN and AP) positively corelated with coffee production.This research shows that coffee pruned with mixed fertilizers (organic and inorganic) according to farmer's doses (T1MD1) is the optimal management for coffee agroforestry systems.

Table 2 .
Matrix of coefficient correlation among soil total N, available P, soil pH, and coffee production