before the runoff collection event, respectively (Table 1). Each
pre-irrigation event consisted of a 12 mm simulated rainfall event
resulting from 10 min of irrigation at a rate of 70 mm h−1. Treatments
without irrigation were subjected to the runoff collection
event immediately after biosolids or MF application. The runoff
collection event captured 30 min of runoff and began when flow
from the collection gutter became continuous. These rainfall scenarios
were selected to quantify the effect of small rainfall events
(e.g. 12 mm) on nutrient losses in runoff when compared to a worst
case scenario where a large, runoff-producing rainfall occurs within
hours after application of the amendment. The probability that
50 mm of rain will fall in 24 h is less than 2%, and the probability
that 25 mm of rainfall will occur in 24 h is approximately 4%
based on over 100 yr of precipitation data from the Wright County,
MO, area (High Plains Regional Climate Center, 2010). However,
the likelihood of a 13 mm rainfall occurring in 24 h is nearly 10%.
Therefore, it is more likely that small rainfall events will occur after
biosolids or MF applications before a larger rainfall event generates
runoff.