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Over-fertilization is a common practice in ornamental nursery production. Oftentimes, visual analysis is used to determine plant nutrient levels, leading to less accurate estimates of fertilizer application. This study focused on exploring the suitability of two non-destructive sensors, Soil Plant Analysis Development (SPAD-502) and GreenSeekerTM, for measuring plant tissue nutrient uptake. Florikan Top-Dress fertilizer 12N-6P-8K was applied to Justicia brandegeana in various increments (0, 10, 20, 30, 40, and 50 g) to simulate plants with deficient to excessive nitrogen rates. Various parameters were recorded including Normalized Difference Vegetation Index (NDVI) and SPAD readings, soil leachate analysis (nitrates and phosphate), and total leaf carbon:nitrogen (C:N). The NDVI and SPAD readings were recorded biweekly for three months after the initial controlled release fertilizer (CRF) treatments. Leaf C:N was analyzed through dry combustion while nitrates and phosphate were determined from soil leachate. Results suggest that the smaller amount (20 g) of CRF is as effective in providing N to J. brandegeana as larger amounts (30, 40, 50 g). Implementation of this fertilizer regimen will result in reduced agricultural nutrient runoff and overall negative environmental impacts. Application of optical sensor technology using SPAD and GreenSeekerTM showed promising results in determining the fertilizer requirements of J. brandegeana. This method could serve as a guideline for nursery producers and landscape personnel as a fast and non-destructive tool for sustainable fertilizer management practices within the ornamental plant industry.

Agricultural practices, specifically crop and land management schemes, greatly influence the ability of soil to produce CO2 under varying conditions. A 2-year research study was planned to quantify carbon-dioxide (CO2) emission fluxes and total C (TC) contribution in a no-till tropical soil under carambola with sunn hemp-velvet bean cover cropping (CC) systems. Composted poultry manure (PM) was applied as an additional N source. The treatments were fallow control (F), fallow with PM (FM), sunn hemp (SH), SH with PM (SHM), velvet bean (VB), and VB with PM (VBM). Average daily CO2 emission from VB was 23 and 15% higher than control and SH plots, respectively, during CC growing season. Similarly, CO2 emission after CC termination was highest from VB plots. About 17% higher CO2-C emission was observed from manure applied plots which indicates that additional food sources stimulated microbial activity in the soils and subsequently produced more CO2. However, total C contribution in SH plots were significantly higher than in VB plots and was more apparent when manure was not applied. Soil and air temperature played key roles in CO2 emission, specifically during the CC growing season. Considering both input and output parameters of C in the soil, our results suggest that SH has the better potential in reducing CO2 emission and accumulating more C in the soil than VB in tropical fruit orchard.

This document synthesizes information about the warm season cover crop sunn hemp. The question-and-answer format addresses frequently asked questions for growers with answers that summarize the growing body of sunn hemp research. The information is provided so that growers in Florida can learn about up-to-date cultivation and management options for sunn hemp as well as better understand its practical uses. This document is a follow-up to the following: Wang, Qingren, Yuncong Li, Waldemar Klassen, and Edward Hanlon. 2015. “Sunn Hemp : A Promising Cover Crop in Florida”. EDIS 2015 (7), 4. https://doi.org/10.32473/edis-tr003-2015. Wang, K., and Robert McSorley. 2004. “Management of Nematodes and Soil Fertility With Sunn Hemp Cover Crop”. EDIS 2004 (18). https://journals.flvc.org/edis/article/view/114109.