Nutrient management in coffee-based agroforestry systems plays a critical role in soil nitrogen (N) cycling, but has not been well documented. The objective of this study was to evaluate the effect of coffee canopy management and fertilization on soil N dynamics. This study used a randomized complete block design (2 × 3 × 2) with four replications. There were three factors: 1) coffee canopy management (T1: Pruned, T2: Unpruned), 2) fertilizer type (O: Organic, I: Inorganic; M: 50% Organic + 50% Inorganic), and 3) fertilizer dose (D1: low, D2: medium, D3: high). Soil N dynamic indicators (i.e., total N, ammonium (NH₄⁺), nitrate (NO₃⁻), net N-NH₄⁺, net N-NO₃⁻, soil microbial biomass N) were measured at two soil sampling depths (0–20 cm and 20–40 cm). Results showed that pruning increased soil total N and microbial biomass N (MBN) by 10–56% relative to unpruned coffee trees. In contrast, the unpruned coffee canopy had 15–345% higher NH₄⁺, NO₃⁻, net N-NH₄⁺, net N-NO₃⁻, and microbial biomass N concentration than pruned coffee. Mixed fertilizer application increased NO₃⁻ and net N-NH₄⁺ accumulation by 5–15% relative to inorganic and organic fertilizers. In addition, medium to high dose fertilization led to a 19–86% higher net N-NO₃⁻ concentration and microbial biomass N as compared to low dose fertilization. The treatment of no pruning and mixed fertilizer at low to medium doses was the optimal management strategy to maintain soil available N, while pruning combined with organic fertilizer has the potential to improve soil total N and MBN.

The range between boron deficiency and toxicity in plants is utterly narrow, so that the certain dose of boron fertilizer is required for plants. Indicators of optimum boron fertilization can be measured from plant production and boron use efficiency (BUE) value. BUE influenced by the amount of soluble B-soil, type of B fertilizer, amount of boron input, type of plant, and adequacy of available macronutrients (NPK). However, excessive application of NPK base fertilizer from inorganic fertilizers can trigger soil degradation. Currently, there has not been much research that measures the reduction in the dose of NPK base fertilizer combined with boron fertilizer on plant BUE. The combination of reducing the dose of NPK base fertilizer and boron fertilizer was tested on sweet corn plants on production and BUE. This study was conducted with a randomized block design with 7 treatments, namely without fertilization (K0), base fertilization (D1), 100% base fertilization and 50–15% borate (D2–D4), and 75% base fertilization and 50–15% borate (D5–D7). The results of the initial soil analysis showed low boron content in the soil, so borate fertilization was required to provide nutrients for sweet corn plants. Application of NPK base fertilizer (100%) and addition of borate fertilizer at a dose of 50-100% (~3-6 kg/ha) significantly increased growth, plant biomass, B uptake, boron recovery efficiency (BRE), and B fertilizer efficiency ratio, compared to lower NPK-base fertilizer. Based on the estimated response curve, the recommended dose to achieve optimum-maximum sweet corn production and maximum boron recovery efficiency is 100% macro inorganic fertilization (urea, SP-36, KCl) combined with 5.72-6.75 kg/ha borate fertilizer.

The low nitrogen-use efficiency (NUE) in sandy soils, due to high porosity and poor nutrient retention, necessitates proper management in fertilization. This study aims to evaluate the effect of biochar-coated urea (BCU) with different coating thicknesses and nitrogen doses on soil nitrogen content, nitrogen uptake, NUE, growth, and yield of sweet corn in sandy soil. The experiment used a factorial randomized block design with two factors, including biochar coating thicknesses (i.e., 14% and 29%) and fertilization doses (i.e., 50%, 100%, 150%, 200%, and 250%). The results showed that the 29% biochar coating thickness led to 9.9–21.3% higher plant height, N uptake, and N-use efficiency, but it led to 22.8% lower yield, as compared to the 14% biochar coating thickness. Additionally, the application of BCU doses of 100% and 150% (~161 and 241.5 kg N/ha) led to 9.2–97.3% higher maize growth, yield, N uptake, and NEU as compared to the other doses (i.e., 50%, 100%, 250%). This study confirmed that the combination of a 29% biochar coating thickness with 150% of the recommended BCU dose (~241.5 kg N/ha) was the best combination, resulting in the highest N uptake, growth, and yield of maize.