Suarau Odutola Oshunsanya and Tolafe Olayinka Adeniran
The quality of untreated water used by dry season vegetable growers determines the safety of the vegetables produced for human consumption. Traditionally, small scale vegetable farmers site their farms along banks of streams which gradually dry up during the dry season resulting in isolated pockets of ponds at different intervals along the path of the streams which are used by farmers to irrigate. A field experiment was initiated at Ibadan to ascertain the quality of irrigation water used to produce vegetables along Ona-stream during the dry season. Five isolated ponds and one locally dug well were sampled and analysed to ascertain the heavy metals status. Results of soil analysis from five farms (A - E) sited very close to the stream revealed high concentrations of heavy metals ranging from 0.96 to 2.34 mg kg-1 for Pb, 0.72 to 2.16 mg kg-1 for Cr and 0.30 to 0.92 mg kg-1 for Co while farmland F sited about 90m away from the stream was free of Pb, Cr and Co contaminants. Locally dug well F water was free of Cr, Co and Pb while isolated ponds had Cr, Co and Pb in the range of 0.01 to 0.23 mg kg-1 which is beyond safe consumption thresholds. There were strong correlations between heavy metals in water and vegetable for Cr (0.992**), Cd (0.599**), Ni (0.614*) and Pb (0.552**) indicating that the hygienic status of dry season vegetables is largely determined by the quality of irrigation water. In addition, all vegetables irrigated with untreated isolated ponds contained Cd, Pb and Ni concentrations above maximum permissible standard which could pose risk to human health. Therefore, farmers should be enlightened on the need to use hygienic water for irrigation. Construction of shallow wells on the farms instead of using contaminated stream water directly could be a better option for healthy and sustainable agriculture.
Accurate quantification of irrigation water requirement at different physiological growth stages of okra (Abelmoschus esculentus L.) life cycle is important to prevent over or under irrigation. Field experiments were therefore initiated to model okra irrigation water requirements at the four physiological growth stages of okra life cycle using CROPWAT model. Derived savannah 1 (DS1), derived savannah 2 (DS2) and humid forest (HF) occupying 493.36 ha, 69.83 ha and 305.25 ha respectively were used. Some selected soil physical properties coupled with weather parameters were used to develop irrigation water requirements for okra crop. In DS1, the estimated crop co-efficient (Kc) values were 0.30, 0.52, 0.84 and 0.70 for the germination, crop growth, flowering and fruiting stages, respectively. Corresponding Kc values in DS2 were 0.30, 0.54, 0.90 and 0.84 and in the HF were 0.30, 0.56, 0.87 and 0.86 respectively. Daily crop evapo-transpiration values ranged from 1.16 to 3.36, 1.17 to 3.64, and 1.2 to 3.38 mm day-1 for DS1, DS2 and HF respectively with significant (p = 0.05) peak at the flowering stage for the three locations. Sustainable okra cultivation would require maximum daily irrigation water at flowering stage (reproductive phase) to meet the crop physiological needs and evapo-transpiration demand of the atmosphere.
The universal soil loss equation (USLE) and water erosion prediction project (WEPP) (inter-rill and rill) erodibility factors are important indicators for land degradation assessment all over the world, which were primarily developed for the United States of America (USA). However, information on suitability of USLE and WEPP for tropical environment is scarce. Therefore, studies were carried out to investigate the suitability of USLE and WEPP for selected tropical soils of Southwestern Nigeria. Four pedons classified based on USDA soil taxonomy as Plinthic Petraquept (Adio series), Kanhaplic Haplaustalf (Oyo series), Typic Plinthustalf (Temidire series) and Typic Haplaustalf (Owutu series) were used for the study. Soil erodibility factor was determined using USLE and WEPP models. Origin-Pro. 8.1 software was employed to compare USLE and WEPP models for conformity and suitability. The results showed perfect agreement (R2 = 1.0; P < 0.001) between the two WEPP (inter-rill and rill) erodibility models in all the four soil types investigated. In addition, WEPP models (inter-rill and rill erodibility) significantly (R2 = 0.82; P < 0.001) related to USLE (El-Swaify and Dangler, 1977) erodibility model. There was a poor relationship (R2 = 0.46; P < 0.06) between USLE (Wischmeier and Mannering, 1968) and the WEPP erodibility factors. The WEPP erodibility models with a perfect relationship with soil properties of the four soil types are more suitable than USLE models for predicting soil erodibility of the identified soil types in tropical environments.