The frequency of fertilizer application increases linearly with the age of the farms in both sites and consequently, with high rates of NPK 20 10 10 which might contribute not only to degradation but also to the pollution of these soils.The two most common ways of fertilizer applications in Nkolbisson and Nkolondom III sites are by simple spreading and landfilling. These fertilizers are applied at 93% by simple spreading and 8% by landfilling at the Nkolondom III site . At Nkolbisson, only simple spreading is used for fertilizer application. In most cases 35.4% of these fertilizers are applied during planting, but in a few cases it is done at 4.9% several months before planting.It is worth noting that in Nkolbisson water used to irrigate vegetables have a dual origin; where 40% are from small wells build near the plots and 60% from the streams .

The water used to irrigate vegetables in Nkolbisson comes only from Abiergue stream which is highly polluted because it is the dumping ground for various excrement , waste and waste water from hospital, washing cars, motorcycles, harvested products, equipment used for the application of pesticides, as well as clothes and discarded dishes and traffic jam. Conversely, the irrigation water used inNkolondom III comes from the Kankouna River, which appears to be less polluted because human activities are less accentuated around and in this watercourse .Agricultural pesticides mainly insecticides and pesticides are applied at very high rates by farmers at the Nkolbisson and Nkolondom III sites. Most have not been trained on the management of these products .Fertilizer application is never done after soil analysis in both Nkolbisson and Nkolondom III sites, leading to several consequences ranging from improvement to degradation of soil structure according to the number of years of exploitation .

There is a potential degradation of 4.5% to 50% and 8.3% to 70%, as well as a change in soil properties in the range of 14.3% to 60% and 15% to 44% in Nkolbisson and Nkolondom III respectively. This worrying degradation coupled with the modification of soil properties is highly observed in plots of more than 26 years old at Nkolbisson, and above 16 years old at Nkolondom III. This degradation highlights the negative impact of the high use of chemical fertilizers on soil resources in these sites. A decline in crop production from 60% to 8% and 98% to 39% was observed and also the quality of the soil structure from 30.8% to 2% and 60% to 9% in the two sites .The socioeconomic data from the survey showed that farmers of the Nkolbisson and Nkolondom III sites are of equal proportion of men and women; Contrary to the trend observed in the Nkolbisson site in 2010 by Kouam and et al. . This situation may be due to urbanization, lack of jobs and dynamism of women who are now also conducting activities out of their homes. vegetable farming are mostly done at the Nkolbisson site by farmers age between 0 to 60 years while at Nkolondom III, it is carried out by those age over 30 years old.

Most vegetable farmers lack training in agriculture from both sites at Nkolbisson and Nkolondom III. This could be explained by the “high” level of intensification of this activity exerted on these soils. Indeed, new plots are more exploited compared to old plots because farmers consider that the for-mer is more productive than the latter. This justifies the high rates of fertilizers applied on the older farms. The fact that most farmers lack training on the application of chemicals products can be a major problem for health and the environment as raised by Kanda et al. . Their level of education indicates a poor knowledge on the use of pesticides, their remanence, their degree of pollution and their limit of efficiency according to the movement of pests . The level and type of training of farmers explain the regression of the frequency of exploitation of the soils according to the number of years under use. Thus, vegetable farming is practiced with techniques that are inadequate for sustainable production, which leads to a change in land use .

The continued and high rate applications of chemical fertilizers in vegetable farming increases the health, soil and water pollution risks . This could result in the degradation of groundwater quality, soil structure and changes in physicochemical properties, thus significantly reducing their fertility . Wastewater used in this agriculture increases the risk of food and groundwater pollution.These waters are suspected to be loaded with pollutants, Fecal Coliforms, Fecal Streptococci , which is not in line with the guidelines prescribed by OMS. Human activities will have to be reoriented in these areas in order to guarantee the nutrition and health of the populations.