Excessive fertilizer application, majorly nitrogen- and phosphorus-based fertilizers, in farmland has intensified environmental pollution of rivers, lakes, and other surface water bodies worldwide by agricultural non-point sources, especially the highly-mobile nitrogen. To solve nitrogen pollution in sugarcane areas, exploring the nitrogen output characteristics of agricultural watersheds in crop fields becomes necessary. Therefore, the objective of the study was to evaluate the characteristics of nitrogen output during typical rainfall events in different sugarcane growth stages in a southern tropical watershed in China. Dynamic monitoring of runoff and nitrogen concentration was carried out for four rainfall events and compared among four sugarcane growth stages (Establishment; Vegetative growth; Grand growth; Ripening) during the growing season of 2018 in the Nala watershed, Kelan Reservoir, Guangxi, China. The results showed that the total dissolved nitrogen flux of the 4 rainfall events ranged from 0.08 to 9.88 kg·hm⁻² for the different growth stages. Nitrate nitrogen was the main component of the total flux, accounting between 75.7 and 92.1% of the total dissolved nitrogen while ammonium nitrogen accounted between 1.80 and 5.26% of the total flux for the 4 rainfall events. Total dissolved nitrogen and nitrate-nitrogen were significantly and negatively correlated with runoff (p < 0.05), while total dissolved nitrogen concentration did not correlate with runoff. The incipient scouring effect of total dissolved nitrogen and nitrate-nitrogen was not noticeable. The concentration of total dissolved nitrogen in the Nala watershed was inferior to class V water quality standard, indicating water eutrophication danger. The study showed that nitrogen nutrient inflow into the river was promoted by N-fertilization time and rainfall. Therefore, reasonably reducing N-fertilization dose and post-rain fertilization could effectively reduce nitrogen inflow into rivers and avoid the intensification of eutrophication in sugarcane areas. We recommend multiple years of studies to verify the possible impacts of differences in weather conditions.

Irrigation scheduling is important for efficient use of applied water and for maximizing crop yields. Therefore, the aim of this study was to evaluate the short-term effect of drip irrigation frequency on soil hydro-physical properties of an Alfisol and performance of two maize varieties, at the Teaching and Research Farm, Faculty of Agricultural Sciences, Ekiti State University, Ado Ekiti, Southwest Nigeria. The experiment was laid out using a split-plot experiment in randomized complete block design (RCBD) and three replications. Irrigation frequency constituted the main plot namely: irrigation four times a week (I4), irrigation thrice a week (I3), and irrigation twice a week (I2) of re-filling soil to field capacity while the subplot was maize variety namely: V1: SAMMAZ-27 and V2: OBA-super-6. Plant growth parameters and soil physical properties of soil water content (SWC), bulk density (BD) and saturated hydraulic conductivity (Ksat) were monitored during the growing cycle. Water use efficiency (WUE) and yield components were determined at maturity. There were significant interactions between irrigation regime and maize variety on SWC and Ksat. The maximum bulk density (BDmax) and optimum soil water content SWCopt were 1.41 g/cm3 and 0.12 g/g, respectively. Plant height (PH) did not differ between the two maize varieties throughout the growth cycle. Drip irrigation frequency did not significantly affect plant height until growth stage V12 (12 fully opened leaves), with I4 irrigation treatment having the tallest plant. Both drip irrigation and maize variety had no significant influence on both LAI and CC, neither was there any significant interaction effect. Increasing irrigation water increased maize yield and yield components. The treatment combination of I4V1 had the highest performance indices in terms of yield components. WUE decreased with increasing frequency of irrigation water application while the WUE of SAMMAZ-27 > OBA-super-6. Therefore, irrigating four times a week and SAMAZ-27 maize variety could be a suitable irrigation-variety combination for providing sustainable irrigation agriculture for maize in this region.

The increased demand for irrigation to boost food supply has placed emphasis on the use of wastewaters. However, the indiscriminate use of wastewaters could impair soil functions and influence other hydrologic processes. The objective of this study was to evaluate soil hydrophobicity and evapotranspiration of two indigenous vegetables under wastewater irrigation in southwest Nigeria. The study was a factorial experiment, laid out in randomized complete block design (RBCD) with three replications. The vegetable factor consisted of SM - Eggplant (Solanum macrocarpon) and CA – Lagos spinach (Celosia angentea), while the wastewaters were abattoir wastewater (AW), bathroom and laundry wastewater (BW) and cassava effluent (CE), with rainwater (RW) as control. Soil hydrophobicity was determined before the experiment and after harvest using water-droplet penetration time (WDPT) method while the crop evapotranspiration was determined using soil water balance technique. Wastewater irrigation significantly (p<0.05) influenced soil hydrophobicity, as the initially wettable soil became slightly hydrophobic, with the highest degree from CE wastewater. The evapotranspiration of both vegetables was significantly (p<0.05) affected, with none of the wastewater treatments dominating the temporal distribution of crop evapotranspiration. Continuous application of wastewater for irrigation could increase the level of water repellency, affect soil water dynamics and availability. Key words: Soil water repellency, wastewater effluent, evapotranspiration.

Aims: The objective of this study was to evaluate water quality status of rivers OBA, ORA and SUNSUN for irrigated agriculture in Ogbomoso, Southwest Nigeria. Study Design: Data were analyzed using 2 x 3 factorial design, with two sampling sites and three sampling periods as treatments in three replications. Place and Duration of Study: The experiment was conducted in six Fadama sites along three rivers (Oba, Ora, and Sunsun) in Ogbomoso located on Latitude 8° 10’N and Longitude 4° 10’E, about 342 m above the mean sea level, southwest Nigeria between December 2014 and March 2015 during the 2014/2015 irrigation (dry) season. Methodology: Water samples were collected from two representative Fadama sites along each river and at three different periods during the 2014/2015 irrigation season for the determination of water quality indicators and overall water quality index (WQI). Results: There was significant temporal variation in the water quality indicators of the three rivers. Except for permeability index (PI), other integrated water quality characteristics of SAR, KI, SSP, ESP, MI and RSC varied significantly (p<0.05) with respect to sampling site and period, and the average values were within permissible limits for irrigation. Of the three rivers, only River SUNSUN had salinity and sodicity classification of C3-S1 and water quality index of class III during a particular period. Conclusion: The results from SUNSUN River showed that care must be taken in using the river for irrigation, especially at the peak of dry season, because of salinity problem. Further studies is also recommended for heavy and trace metals contamination as a result of the observed anthropogenic activities in the vicinity of the river bodies.