The implementation of the SPAD-502 Chlorophyll meter for the quantification of nitrogen content in Arabica coffee leaves.

The utilization of a non-destructive SPAD-502 chlorophyll meter, which enables the measurement of nitrogen status in plant leaves, has gained popularity in agronomic crops. Its application to horticultural crops like coffee remains relatively uncommon. The device provides quick and real-time measurements, helping to provide on-time nitrogen fertilizer to coffee plants before deficiency signs occur. Coffee leaves are characterized by thick and waxy leaves, together with many layers of tree crown. Therefore, the objective of this study was to develop a method for measuring nitrogen levels in coffee plants using the SPAD-502 Chlorophyll meter for an appropriate nitrogen fertilizer application rate in Arabica coffee plants. •Coffee trees were separated into upper, middle and lower levels. Data on SPAD values and total nitrogen were analyzed.•Pearson Correlation Coefficient (R), Coefficient of Determination (R2) and linear regression were calculated for different three levels of both SPAD-502 and total nitrogen values.•The results revealed a strong correlation (R2 = 0.63) between the SPAD readings of coffee leaves obtained from the upper canopy and their nitrogen content. These findings can provide a good concept of which coffee crown level will be a better part for measuring N content using a SPAD-502 Chlorophyll meter.

Dynamics of soil nitrogen availability following conversion of natural forests to various coffee cropping systems in northern Thailand.

Land conversion critically affects soil physiochemical and biological properties, yet very little remains clear about the impact of forest conversion on the N pool and related microbial N transformations. Therefore, this study aimed to examine the dynamics of soil N availability following forest conversion into the different coffee cropping systems, and explore the mechanisms behind these dynamics from the microbial N transformation. Disturbed soil samples from two depths (0-20 and 20-40 cm) were collected from four land uses consisting of three different coffee cropping systems (coffee monocultures (C), coffee agroforestry (FC), coffee associated with persimmon (Diospyros kaki L.) (CH)) converted from natural forest and adjacent natural forest (F) in northern Thailand. The soil labile N pools (including ammonium (NH4+), nitrate (NO3-), inorganic N (IN), dissolved organic N (DON) contents and microbial biomass N (MBN)) were measured, as well as the soil total N (STN) content. Soil N transformation rates, including net N mineralization, nitrification, and immobilization, were determined using a laboratory incubation experiment. The results showed that the forest conversion to coffee agroforestry significantly increased soil N content by 39.83 % in topsoil, but no significant difference was observed in C and CH soils as compared to F soil (p ≤ 0.05). The three labile N forms (NH4+, NO3- and DON content) were significantly higher under the C, FC and CH soils in both depths, while the coffee monoculture decreased the MBN content. The increases in soil IN, IN/DON and NO3-/NH4+ ratios used as an N availability indicator were positively associated with an increase in the N mineralization and nitrification processes following the forest conversion. Interestingly, the N immobilization processes in the F and FC soils were significantly higher than those in the C and CH soils, which indirectly regulated a decreased nitrification rate in F and FC soils in our study. With the exception of the FC soil, the nitrification/N immobilization ratios in the C (4.95) and CH (4.08) soils were higher than those in the F (0.70) soil, indicating an increased N loss risk after forest conversion. Therefore, coffee agroforestry systems have the potential to be effective management strategies for improving soil nitrogen sequestration following forest conversion.