C. Rotz

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Armando Marques-Guedes

UNL - New University of Lisbon

Heather D Baker

University of Toronto

Viacheslav Kuleshov

Stockholm University

Mohamed Ahmed Youssef

Al-Azhar University

Francisco Mesias Diaz

Universidad de Extremadura

Aydin Mohseni

Carnegie Mellon University

Andrew Leach

The University of Sydney

erika lück

Universitaet Potsdam

Sean Clark

Berea College

Maria Niklińska

Jagiellonian University

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Papers by C. Rotz

The challenges – and some solutions – to process-based modelling of grazed agricultural systems

by C. Rotz and Roger Martin-Clouaire

Measures of Nitrogen Use Efficiency and Nitrogen Loss from Dairy Production Systems

Journal of Environment Quality, 2015

In dairy production systems, tradeoffs can occur between fertilizer N applications and crop N use... more In dairy production systems, tradeoffs can occur between fertilizer N applications and crop N use, feed N consumption and manure N excretion, and environmental impacts. This paper examines (i) how stocking rates affect N imports and management on dairy farms, N use efficiency (NUE; i.e., the amount of applied N incorporated into product N), and N loss; (ii) how reductions in fertilizer N and feed N may affect crop and milk production, NUE, and N loss; and (iii) why tradeoffs in N use outcomes should be considered when attempting to enhance overall NUE and reduce N loss. The Integrated Farm Simulation Model simulations of two representative dairy farm types and analyses of regional studies, long-term field experiments, and cow nutrition trials were used to demonstrate that (i) stocking rate affects cropping patterns, fertilizer and feed imports, and N loss; (ii) although fertilizer N reductions of 20 kg N ha may reduce slightly the crude protein (CP) content of corn silage (which would require purchase of additional CP supplements), this practice should not affect long-term corn yield but would reduce nitrate (NO) and nitrous oxide (NO) losses by 13 to 38%; (iii) dietary CP could be reduced on many dairy farms, which would not affect milk production but would reduce ammonia (NH) and NO emissions by 15 to 43%; and (iv) greater recognition of the tradeoffs in N use and N loss are needed to provide a better understanding of the potentials to enhance overall NUE and reduce environmental N loss from dairy production systems.

Alfalfa and Corn Silage Systems Compared on Michigan Dairy Farms

Journal of Dairy Science, 1997

Two primary roughages used for diets of dairy cows are corn silage ( Zea mays L.) and alfalfa ( M... more Two primary roughages used for diets of dairy cows are corn silage ( Zea mays L.) and alfalfa ( Medicago sativa L.). A dairy forage system model was used to compare the relative merits of these two forages when varied amounts (none, one-third, two-thirds, and all on a dry matter basis) of the forage requirement were ammoniated corn silage and the remainder was alfalfa. Primary comparisons were the net return above feed and manure costs, but manure management issues and labor requirements were also considered. Economic comparisons were made for representative farms using a partial budget analysis synthesized from research reports and surveys. The highest net return was from alfalfa at 100% of the forage requirement, but differences in net returns across forage systems were small compared with the variation caused by weather among years. Changes in assumptions concerning farm size, soil type, crop yield, milk production, relative prices, and manure handling did not affect the conclusions of the analysis. In systems that used all alfalfa forage, much of the manure was applied to alfalfa crops, a practice that is normally discouraged because the manure reduces weed control, stand persistence, and yield. With alfalfa at 100% of the forage requirement, large amounts of excess manure nitrogen were produced on the farm. Application of nitrogen to alfalfa must be compensated by a reduced nitrogen fixation to avoid ground water contamination. Because of the lack of a strong economic advantage among the forage systems, the practice of having at least one-third of the forage requirement provided by each of the forage crops is favored to improve management of crops, manure disposal, and labor. ( Key words: corn silage, alfalfa, forage systems, economics)

C. Rotz

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