Glyphosate-based herbicide products are the most widely used broad-spectrum herbicides in the world for postemergent weed control. There are ever-increasing concerns that glyphosate, if not used judiciously, may cause adverse nontarget impacts in agroecosystems. The purpose of this brief review is to present and discuss the state of knowledge with respect to its persistence in the environment, possible effects on crop health, and impacts on crop nutrition.

Citrus ( Citrus sp.) root length density (RLD) can help in understanding and predicting nutrient and water uptake dynamics. A study was conducted at two sites in Florida to investigate root and water distribution patterns among different irrigation and fertigation systems. The results over the 2 years showed that RLD was highest in the 0- to 15-cm soil depth and decreased with depth for all treatments at both sites. About 64% to 82% of the fibrous roots (<1 mm diameter) were concentrated in the irrigated zones of drip- and microsprinkler-irrigated trees and 18% to 36% were found in the nonirrigated zones at the Spodosol site (SS). At the Entisol site (ES), the RLD (<0.5 mm diameter) in the 0- to 15-cm depth soil for intensive microsprinkler or drip irrigation was 3- to 4-fold (nonirrigated zone) and 4- to 7-fold (irrigated zone) greater at the 0- to 15-cm soil depth than that for conventional irrigation system. The trees at SS were symptomatic for Huanglongbing (HLB; Candidatus Liberibacter asiaticus ) in the second year, while those at ES were asymptomatic throughout the study. This might have limited the density and extent of root distribution at SS. The water contents remained either close to or slightly above the field capacity. The results showed higher RLD for intensive irrigation and fertigation practices in irrigated zones compared with conventional grower applications suggesting greater water and nutrient uptake potential for the former.

Understanding citrus tree root development and dynamics are critical in determining crop best nutrient management practices. The role of calcium (Ca) and magnesium (Mg), manganese (Mn), Zinc (Zn), and boron (B) on huanglongbing (HLB) affected citrus trees’ root growth and lifespan in Florida is not fully documented. Thus, the objective of this study was to determine the impact of foliar and ground-applied essential nutrients on seasonal fine root length density (FRLD; diameter (d) < 2 mm) and coarse roots (d > 2 mm), FRLD dynamics, root survival probability (lifespan), and root-zone soil pH of HLB-affected sweet orange trees. Results indicated that Ca treated trees budded on Cleopatra (Cleo) and Ca and Mg combined treatments on Swingle (Swc) rootstocks significantly increased seasonal FRLD of fine (< 2 mm) and coarse roots. The highest median root lifespan of Ca treated trees was 325 and 339 days for trees budded on Cleo and Swc rootstocks, respectively. In the second study, the coarse roots showed a significantly higher reaction to the nutrition applied than the fine roots. Meanwhile, the 2× (1× foliar and 1× ground-applied) treated trees showed a significantly higher median root lifespan compared to the other treatments. Thus, the current study unwraps future studies highlighting the combined soil and/or foliar application of the above nutrients to stimulate FRLD and improve root lifespan on HLB-affected sweet oranges with emphasis on root-zone soil pH.

Citrus greening, also called Huanglongbing (HLB), has affected citrus production globally. In Florida, the disease has decimated citrus production area and overall fruit yields. Emerging results show that some nutrients applied in a balanced and constant nutrition (BCN) program alleviate tree stress by improving root health, canopy size and tissue nutrient concentration. In this paper, we discuss the current strategies for managing citrus in Florida, and roles of macro- and micronutrients in citrus and other crops. Further, we discuss the role of macro- and micronutrients in potentially restoring root health and tree performance. We wrap up by discussing future research opportunities on the health and nutrition of HLB-affected citrus trees.

Small-scale irrigation continues to cushion the food security gap in sub-Saharan Africa. Irrigation is largely governed by water availability, soil type and crop water requirements, among other factors. Thus, a study was conducted to assess the suitability of various water sources for irrigation in northern Ghana. Specifically, the study sought to assess quality of water sources in the Savelugu, Kasena-Nankana East, and Nabdam districts for small-scale irrigation development. The water quality parameters used were: pH, electrical conductivity (EC_w), sodium adsorption ratio (SAR), sodium percent (Na%), soluble sodium percentage (SSP), magnesium adsorption ratio (MAR), Kelley9s ratio (KR), total hardness (TH), Chloride (Cl), E. coli, and Feacal coliforms. While we found most of the irrigation water sources, including small reservoirs, dams, wells and rivers suitable, few unsuitable irrigation water sources were also identified. Overall, the study found that opportunities for scaling small-scale irrigation exist in all the sites. The knowledge generated from this study will guide irrigation water use, and agricultural policy for sustainable smallholder irrigation development in the region.

The decrease in the rate of inflow and outflow of water—and thereby the uptake of plant nutrients as the result of Huanglongbing (HLB or citrus greening)—leads to a decline in overall tree growth and the development of nutrient deficiencies in HLB-affected citrus trees. This study was conducted at the University of Florida, Southwest Florida Research and Education Center (SWFREC) near Immokalee, FL from January 2017 through December 2019. The objective of the study was to determine the effect of rootstocks, nutrient type, rate, and frequency of applications on leaf area index (LAI), water relations (stomatal conductance [g_s], stem water potential [Ψ_w], and sap flow), soil nutrient accumulation, and dynamics under HLB-affected citrus trees. The experiment was arranged in a split-split plot design that consisted of two types of rootstocks, three nitrogen (N) rates, three soil-applied secondary macronutrients, and an untreated control replicated four times. LAI significantly increased in response to the secondary macronutrients compared with uncontrolled trees. A significantly greater g_s, and thus a decline in Ψ_w, was a manifestation of higher sap flow per unit LA (leaf area) and moisture stress for trees budded on Swingle (Swc) than Cleopatra (Cleo) rootstocks, respectively. The hourly sap flow showed significantly less water consumption per unit LA for trees that received a full dose of Ca or Mg nutrition than Ca + Mg treated and untreated control trees. The soil nutrient concentrations were consistently higher in the topmost soil depth (0–15 cm) than the two lower soil depths (15–30 cm, 30–45 cm). Mobile nutrients: soil nitrate–nitrogen (NO₃-N) and Mg²⁺ Mg²⁺, Mn²⁺, Zn²⁺, and B leached to the lower soil (15–30 cm) depth during the summer season. However, the multiple split applications of N as Best Management Practices (BMPs) and optimum irrigation scheduling based on reference evapotranspiration (ET_o) maintained soil available N (ammonium nitrogen [NH₄-N] and NO₃-N) below 4.0 mg kg⁻¹, which was a magnitude 2.0–4.0× less than the conventional N applications. Soil NH₄-N and NO₃-N leached to the two lower soil depths during the rainy summer season only when trees received the highest N rate (280 kg ha⁻¹), suggesting a lower citrus N requirement. Therefore, 224 kg ha⁻¹ N coupled with a full Ca or Mg dose could be the recommended rate for HLB-affected citrus trees.