Two-dimensional monitoring of soil water content in fields with plastic mulching using electrical resistivity tomography

Plastic mulching (PM) has become an important agricultural practice to improve crop yields worldwide, while there is still a lack of methods to quantify the complex spatial variations of soil water content (SWC) in the PM field. In this study, a methodology for using Electrical Resistivity Tomography (ERT) to get SWC information in the PM field was presented. Its performance in monitoring SWC was validated, and the spatial variation of SWC was analyzed using the ERT results. A simplified Waxman and Smits model was selected to calibrate the pedo-physical relationship, and it showed good performance (coefficient of determination > 0.92). With the calibrated model, the SWC obtained using ERT showed good agreement with soil moisture sensors in different soil layers (RMSE < 0.027 cm3 cm−3). The ERT results showed that rainfall and drying events have different effects on SWC at different growing stages. At the early stage, rainfall and drying events mainly influenced SWC on the bare strip, while at the later stage, rainfall and drying events had more obvious effects on the zone near the planting hole. On a seasonal scale, a higher SWC was not only found in the middle part of the mulched strip, but also in the bare strip, while a lower SWC was found in positions near the planting hole. At the same time, a high-resolution ERT measurement revealed that the SWC was also largely influenced by the soil heterogeneity. As such, SWC in the mulched strip was not necessarily higher than in the bare strip as we had supposed, but showed a high degree of irregularity in two dimensions. Considering the irregularity of SWC in two dimensions, our study calls for replacing point-scale measurement with two-dimensional monitoring methods when acquiring SWC information in a field with PM

APPLICATION OF GEOPHYSICAL AND GEOCHEMICAL METHODS FOR SOIL CHARACTERISATION IN SUSTAINABLE PRECISION AGRICULTURE IN SELECTED FARMS

All soils have potential for high yield for specific crops. Nigerian soils have potential for medium to high yield, but poor farming practices including the misuse of chemical fertilizers result in a number of constraints such as soil salinity, degradation and declining fertility, which militate against high crop yields. Nigeria, currently battling with food insecurity because population growth is not commensurate with agricultural production. Thus, there is need for urgent intervention in the agricultural sector. The aim of this study was to integrate geophysical and geochemical methods for sustainable precision agriculture in two farm sites of Covenant University and Landmark University, Nigeria. In this study, electrical resistivity, geochemical and satellite imagery methods were used for soil characterisation in farm sites at Covenant University, Ota, Southwest and Landmark University, Omu-Aran, North-central Nigeria between June, 2018 and January, 2019. The electrical resistivity data were processed using RES2DINV and Win-Resist software. Geochemical analysis of soil samples from the sites was conducted using ICP-MS in ACME laboratory, Canada. Monthly MERRA satellite data was used to determine the soil temperature and soil moisture content while soil salinity was estimated from Landsat-8 satellite imagery. The study showed that electrical resistivity of the topsoil in Covenant University farm ranged from 120 -500 Ωm, while that of Landmark University farm ranged from 345-527 Ωm. The soil types delineated at the Covenant University farm were clayey sand and lateritic clay; sand/lateritic gravelly sand was delineated at Landmark University farm. Potentially toxic elements were detected in the soil samples of both sites; arsenic (As), chromium (Cr), lead (Pb) and copper (Cu) exceeded FAO/WHO recommended standard limits in Covenant University farm. The pollution indices of Co, Cr, Ni, Pb and Mn in the Covenant University farm were within low to high contamination, while As was within medium to high contamination. In Landmark University farm, the pollution indices of Pb, Cu, Zn, Co and Cd ranged from low to medium, while As has pollution index within low to high contamination. Results showed elevated concentrations of As in all samples. Ca-Mg, P-Mg, Fe-Al, Ca-K, Mg-K and Na-K paired nutrients were positively correlated at 5% level of significance in both farmlands, indicating similar increase in both farmlands. Also, the geospatial maps revealed zones of high and low accumulation of essential macro nutrients within the farmlands. Landmark University farmland indicated higher soil salinity than Covenant University farm land. Soil temperature (ST) data at Covenant University farm ranged from 296 - 314 K, while ST at Landmark University farm ranged from 289 - 317 K. Soil moisture content data for both farms ranged from 23 – 113 3 3 mmand 10 - 110 3 3 mmin Covenant and Landmark University farms, respectively. The sandy gravelly soil of Landmark University farm is suitable for the planting of root and tuber crops such as carrot, yam, potatoes, turmeric and beets. Cabbage, leafy vegetables and lemon grass can be grown successfully in Covenant University farm. The ecological risk assessment of toxic metals, showed that arsenic may present a moderate to very high biological risk to both plants and animals that feed on the soil of both farm lands. The site-specific information of the farm sites has been provided. This study provides database that can serve as useful guide in soil management decision making for better yiel