Agronomic recycling of pepper crop residues: Their influence on soil properties and broccoli crop

The agricultural production in the Murcia Region occupies a very important place in the regional economy and especially in the agricultural land of Campo de Cartagena. The intensive agricultural production has resulted in a diffuse pollution problem due to an excessive use of chemical fertilizers and a large amount generation of post-harvest crop residues resulting after the growing season, especially from greenhouse crops. In this thesis the recycling of crop residues applied as soil organic amendment is proposed to improve soil quality and reduce the use of chemical fertilizer. The crop residues have a great potential as organic amendment in agricultural lands representing a source of both organic matter and nutrients; however it is necessary to study their effect when they are applied in soil. We have evaluated, under laboratory conditions, the medium-term influence of pepper residues (very common in Campo de Cartagena) applied at different rates on carbon and nitrogen dynamics in an agricultural soil. The results highlight the importance of dose when applying crop residues. The addition of pepper residues at low doses (2 g kg-1) produce a net N immobilization in soil, while higher doses (3 and 5 g kg-1) show a net N mineralization of 13.7 and 56.7 mg kg-1. Was also studied the effect of pepper crop residues application on broccoli production compared with the exclusive use of chemical fertilizers. We focused on the effect of crop residues on soil physico-chemical and biochemical properties related to the carbon cycle, soil fertility and broccoli nutrient, yield and quality. The results showed that large application rates of crop residues with a minimum chemical fertilization improved chemical and biochemical soil properties increasing, among others, microbial biomass and some enzymatic activities compared with control. Likewise, positive effects on broccoli quality were found with no negative impact on broccoli yield. Finally, the carbon turnover mediated by soil microbial populations was assessed using isotopic labeling techniques to know the amount of labeled C (13C) incorporated into different organic pools considering the influence of three plant materials and under two management systems. Results indicated that the 13C-glucose was much more assimilated into microbial biomass C in plants-amended samples. However, plants addition also caused a positive priming effect and enhanced mineralization of organic 13C, thus C from glucose was incorporated in a lower proportion into soil recalcitrant and labile carbon in plants-amended soils.