CROP RESPONSE, N AND C DYNAMICS AFTER COVER CROP INTRODUCTION

Cover crops (CCs) exert varying influences on the soil nitrogen (N) cycle and water content (SWC) throughout different crop rotation seasons. A thorough assessment of CC growth patterns, nitrogen accumulation, and mineralization holds crucial importance in optimizing their effects on N, SWC resources, and cash crop performances. Furthermore, introducing CCs into cropping systems alongside organic fertilizers is regarded as a pivotal strategy for enhancing short-term soil organic C (SOC) levels. Within this context, the present thesis examines the short-term effects of introducing CCs in two northeast Italy experimental fields, aiming to achieve four objectives. The first three objectives involve studying the impact of two CC successions (in the experimental farm of the University of Padova “L. Toniolo” in Legnaro) - grasses followed by grasses; and grasses followed by leguminous and brassica species - within a 3-year maize-soybean succession experiment. Specifically, the objectives aim to: (i) evaluate CC performance (aboveground and roots production and N uptake) and their influence on silage maize production and soil nitrates (NO3-) content; (ii) use satellite data and model to monitor CC growth and predict their N contribution to subsequent crops; (iii) study CC effects on soil NO3-, N functional genes (NFGs), and their relation to SWC and crop yield across different season. The fourth objective examines the short-term impact of two CC successions (in the demo farm “Podere Fiorentina” of the local Land Reclamation Authority in San Dona di Piave) - grasses followed by grasses, brassica followed by grasses - alongside organic fertilization matrices and irrigation, within a 4-year maize-soybean crop succession in on-farm experimentation, aiming to assess their combined influence on the short-term SOC stock. All CC treatments showed comparable yields of maize and soybean compared to fallow control (without any weeds control). However, diverse CCs exhibited distinct growth patterns and differently affected soil NO3- and NFGs throughout different phases of crop rotation. Satellite imagery analysis indicated that rye and triticale exhibited accelerated growth rates during the winter season compared to clover, but slower than mustard, which suffered a frost winterkilling. During the growing season both grasses CC reduced soil NO3- content, acting as catch crops, and potentially enhanced microbial-mediated N fixation. Conversely, clover CC exhibited greater residual soil NO3- compared to grasses and promoted microbial-mediated N nitrification. Following the CC residues incorporation, the CC-NCALC model estimated a net N mineralization for all CC residues, excluding N immobilization following triticale root residues. Throughout the ensuing cash crop season, the estimated N release from clover and mustard residues was around 33%, whereas, for triticale, it was about 3% of their total N uptake, with a releasing peak 2 months after their termination. While CCs influenced the temporal variation of SWC, none of the tested CCs competed with subsequent cash crops for water resources. Additionally, the introduction of CCs in a conventional maize-soybean succession did not notably affect short-term SOC content. The use of remote sensing imagery and prediction models for CC residue decomposition exhibits promising potential for optimizing CC utilization. Nonetheless, further analysis incorporating various CC species, environmental variables, and diverse cropping systems is necessary to ascertain their applicability and reliability. NFGs were sensitive N cycle indicators, but their susceptibility to various factors demands careful sampling time to distinguish the main effects under analysis.