Nitrogen recovery and contribution to production agricultural systems are critical services provided by cover crops investigated in this study. Research was conducted to evaluate the effect of simulated residual N (SRN) on N recovery in various winter cover crop systems (CCS) and subsequent effects on corn N uptake. Biomass, C and N measurements, 15N recovery, and sources of N acquisition were quantified among CCS. Subsequently, CCS and SRN effects on corn productivity and N status were quantified. Grass-included CCS had the greatest N scavenging ability by CCS termination, though they had negative or neutral effects on corn N acquisition. Brassicas-included CCS were prolific early season N scavengers, though winterkill may have negated this effect. Legumes-included CCS generally accumulated large quantities of N and had narrow C:N ratios, positively affecting corn N acquisition. This study highlights the importance of context-specific CCS selection for N conservation.

Current interest in cover cropping is focused on enhancing ecosystem services beyond soil conservation. Cover crop (CC) species function uniquely in their effects on ecosystem services when grown in monoculture or mixtures. This research integrated field experiments and a literature synthesis to evaluate the role of cover crops in improving nitrogen (N) management and simultaneously providing multiple ecosystem services. Legume CC fertilized with poultry litter (PL) could replace 101 to 117 kg N ha-1 of fertilizer in corn (Zea mays L.) production. Rye (Secale cereale L.) CC fertilized with PL had a negligible effect on corn production. Biculture fertilizer equivalence ranged between -12 to +75 kg N ha-1. Fertilizer equivalence of legume-containing treatments increased across time. Without CC, fall-applied PL failed to supply N to corn. Ecosystem services of CC and PL illustrate complex species functions. Bicultures produced more total biomass than monocultures in year 1 but less than rye in year 2. Bicultures were as effective in suppressing weeds as rye, produced corn yield similar to legume, and by the second year had similar amounts of available soil N as the legume. Poultry litter effects and interspecific effects cover crop species biomass differed. Rye yield increased, while legume yield decreased slightly in biculture. Poultry litter increased legume N content and a decrease in legume C:N, while rye N content and C:N were unaffected. The synthesis corroborates that mixed and biculture cover crops yield more than the individual component species. Overyielding was transgressive in 60% of cases studied. Mixture effects varied by species: rye and brassica yield increased, while legume decreased in mixtures. The effect of mixed CC on crop yields varied by crop species and management practices, though generally crops increased 8 to 18% overall. This work can be applied to the design of complex CC and PL systems that optimize individual species functions to enhance ecosystem services. / Ph. D. / Current interest in cover cropping is focused on enhancing ecosystem services beyond soil conservation. Cover crop (CC) species function uniquely in their effects on ecosystem services when grown in monoculture or mixtures. This research integrated field experiments and a literature synthesis to evaluate the role of cover crops in improving nitrogen (N) management and simultaneously providing multiple ecosystem services. Legume CC fertilized with poultry litter (PL) could replace almost half of the inorganic fertilizer required by spring corn (<i>Zea mays</i> L.) production. Rye (<i>Secale cereale</i> L.) CC fertilized with PL had a negligible effect on corn production. Fertilizer equivalence of legume-containing treatments increased across time. Without CC, fall-applied PL failed to supply N to corn. Bicultures produced more total biomass than monocultures in year 1 but less than rye in year 2. Bicultures were as effective in suppressing weeds as rye, produced corn yield similar to legume, and by the second year had similar amounts of available soil N as the legume. Poultry litter effects and interspecific effects cover crop species biomass differed as well. Rye yield increased, while legume yield decreased slightly in biculture. Poultry litter increased legume N content and a decrease in legume C:N, while rye N content and C:N were unaffected. The synthesis corroborates that mixed and biculture cover crops yield more than the individual component species. Mixture effects varied by species: rye and brassica yield increased, while legume decreased in mixtures. The effect of mixed CC on crop yields varied by crop species and management practices, though generally crops increased 8 to 18% overall. This work can be applied to the design of complex CC and PL systems that optimize individual species functions to enhance ecosystem services.

Im Rahmen eines vierjährigen Feldversuches wurden der Einfluss von Bodenbearbeitung, Bodenbedeckung und Stickstoffdüngung auf die N-Dynamik und N-Verlagerung während der Winterhalbjahre und deren Nachwirkungen auf die Hauptfrucht der nachfolgenden Vegetationsperiode untersucht. Es zeigte sich, dass sich neben den Prüffaktoren auch Unterschiede der Vorfrucht und des Witterungsverlaufes auf die Höhe der Nitratauswaschung über Winter auswirkten. Generell führte der Anbau von Winterrübsen gegenüber der Brache erwartungsgemäß zu einer Reduzierung des N-Austrages, was sowohl auf die geringeren Sickerwassermengen als auch auf die geringeren Nitratkonzentrationen in der Bodenlösung zurückzuführen war. Die N-Konservierung der Winterrübsen wirkte sich auf die folgende Hauptfrucht positiv hinsichtlich der Stickstoffverfügbarkeit im Oberboden und der N-Aufnahme des Sommerweizens während dessen Standzeit aus. Der Schwerpunkt in der methodischen Vorgehensweise dieser Arbeit lag in der Erfassung der Sickerwassermengen zur Abschätzung der N-Verlagerung anhand der Daten der Nitratkonzentration in der Bodenlösung. Die Durchflussmengen im Boden wurden ausgehend von der klimatischen Wasserbilanz und unter Berücksichtigung der Veränderungen der Bodenwasservorräte bestimmt, die anhand von Messungen der Matrixpotentiale und der Kenntnis der Bodenwassercharakteristika im Profilverlauf des Bodens berechnet wurden. Dieser Ansatz wurde drei weiteren Ansätzen gegenübergestellt. Diese sind die klimatische Wasserbilanz, die klimatische Wasserbilanz unter Berücksichtigung der Veränderungen der Bodenwasservorräte anhand der volumetrischen Wassergehaltsmessung mit Hilfe der TDR-Messtechnik und die Bestimmung der Perkolation mittels Wasserleitfähigkeitsfunktionen und Potentialgradienten. Mögliche Fehlerquellen der verschiedenen Ansätze wurden diskutiert und Schlussfolgerungen für die praktische Versuchsdurchführung gezogen. / The influence of different tillage managements, soil covering and different nitrogen applications on the N-dynamic and N-leaching during winter and their effects during the following vegetation period have been investigated within the scope of a field trial of several years. Beside these treatments, differences of the preceding crop type and climatic conditions showed also effects on the amount of nitrate leaching during winter. The cultivation of winter rape compared to fallow reduced the N-leaching in accordance with the expectations; generally this was the result of lower rates of water flow as well as lower nitrate concentrations in the soil solution. During the successive vegetation periods the N-conservation by the catch crop led to higher nitrate contents in the soil, particularly in the upper layer, and to an increasing N-uptake of the fallowing spring wheat. Focal point of the methodical proceeding of this study was the recording of the downward water movement to estimate the N-leaching in combination with the nitrate concentration in the soil solution. The calculation of the water movement in the soil based on the climatic water balance in consideration of the variation of the soil water content; the changes in the soil water were determined by data of the soil matrix potential and the knowledge of the moisture characteristics of the horizons, their positions and their wideness. This approach was based to present the results, and was then compared with three other ones. These were the climatic water balance, the climatic water balance in consideration of the variation of the soil water content by data of the changes of the volumetric soil water content measured by ‘time domain reflectrometry’ and the calculation of water flow with hydraulic conductivity functions and data of the hydraulic potentials. Possible sources of error of the methods are discussed to draw conclusions for conducting field trials.