Site-specific Nitrogen management in citrus orchard to minimize N pollution

Dolev Termin, Raphael Linker, Tarin Paz-Kagan, Shahar Baram, and Eran Rave

Permanent crops agriculture covers 1.2% of the global land area. Such agricultural land requires the addition of the essential nutrients (nitrogen (N), phosphorous (P) and potassium (K)) to the soil in order to sustain commercial viability. In the agricultural context, N is often regarded as the most critical nutrient, and the soil-related growth limiting factor. The relatively low cost of N fertilizers compared to the possible loss of crop yield has led to its over-application and increased losses of different N-forms into the environment. Nowadays, efforts are being directed toward: (1) optimizing and reducing N application rates, while maintaining crop productivity, and (2) enhance N use efficiency (NUE), thus decreasing N losses. Precision agriculture aims at sustainably optimizing the management of cultivated fields by addressing the spatial variability found in crops and their environment with Site-Specific Management (SSM). Therefore, the overall objective of the proposed project is to develop tree based optimal nitrogen (N) for SSM application to citrus orchard. Derived from this are the following sub-objectives: (1)Identify the spatial and temporal variability in N status across the orchard, (2) Correlate between the temporal (monthly) leaf N status, the “standard” leaf N status and the fruit yield per tree, (3) toping fertigation with tree-based application of controlled release N fertilizer to account for tree N status and needs and (4) correlate spatial and temporal variation pattern in N status to N leaching and NUE using remote sensing applications. There are several ways to estimate NUE including (a) yield produced per unit of fertilizer, (b) biomass production per unit of fertilizer, (c) biomass divided by amount of N absorbed and (d) mass balance ratio between the N taken up by the plant and the applied N. Enhancement of the NUE can be achieved via knowledge of the optimal N nutrient uptake curve, and adjustment of the plant N nutrient status throughout the growing season to fit that curve. The research is conducted in four citrus plots at Kfar-Monash – Hefer Valley. These four plots, which include 270 trees, are fertigated by sprinklers. Analysis of the existing heterogeneity was used to choose 12 representative trees that were sampled at regular intervals. The data will be used to build a fertigation model, which will then be used to develop a site-specific fustigation strategy. The preliminary result shows N variance in soil (NO₃ 0 – 8.84 mg/Kg DM, NH₄ 0 – 5.57 mg/Kg DM) and leaves (1.91-3.25%) at each plot for the chosen trees’ position. Thermal Image shows temperature differences which relate to variation in leaf temperatures and water uptake. The research has begun at November 18 and will focus in the first two years (2018-2020) on data gathering for the fertigation model to be built, while at the next two years (2020-2022) will focus on survey of fertigation making the needed adjustments.