Theoretical analysis of manure transport distance as a function of herd size and landscape fragmentation

ABSTRACT:

Fragmentation of the agricultural landscape increases the distance that manure from confined livestock must be transported in order to be properly recycled. We used simple theoretical models to investigate how this distance is impacted by landscape fragmentation and herd size. An expression for manure distribution cost as a function of farm attributes (herd size, manure spreader capacity, crop phosphorus removal, and manure quantity and phosphorus concentration) was applied to three landscape models with which manure-hauling distances were derived. The landscape models were an analytical expression that assumed manure could be distributed radially from the barn, a randomly generated farm neighborhood model, and actual landscapes of three Wisconsin counties. The model yielded estimates of the distance that a herd's manure must be transported to equal crop removal as a function of the fraction of adjacent land available for manure spreading. The fraction of land unavailable for spreading had little effect on total manure hauling distance until this fraction fell below about 0.4 (depending on herd size), after which it increased dramatically. From purely geometric considerations, a diseconomy of scale resulted with manure hauling distance and herd size. Finally, when 30% of the farmland in a county was made unavailable for manure recycling, it made little difference if the removed parcels were spatially random or clustered into fewer and larger areas.