Alfalfa-Oat-Clo er Pasture for Dairy Cattle


 Grazing on irrigated pastures was begun 14 and 51 days
 earlier during the respective two years (1955 and 1957) but
 terminated on the same dates as the unirrigated. Irrigation in-
 creased the number of calendar days the pasture was grazed by
 69 in 1955-56 and by 51 in 1957. Increases in yield of total di-
 gestible nutrients per acre by irrigation were 1,203 pounds in
 1955-56 and 2,017 pounds in 1957. A summary of results of the
 grazing experiments with unirrigated and irrigated alfalfa-oat-
 clover pastures is shown in Table 3.
 Distribution of Feed Supply and Carrying Capacity of the
 Pasture.-In general, the amount of total digestible nutrients
 obtained from the pasture was highest in spring and then de-
 clined during the summer. The yield of nutrients usually was
 low during the late fall and winter periods. In addition to sea-
 sonal variations in feed supply, there were year to year fluctu-
 ations in distribution. Soil moisture, temperature (cold weath-
 er), and diseases were important factors influencing these vari-
 ations. The amounts of total digestible nutrients obtained from
 the pasture per acre biweekly are shown in Figure 1. The base
 line in the figure represents a suggested uniform level of total
 digestible nutrients per acre selected for the purpose of calcu-
 lating the acreage of unirrigated pasture to plant for a herd.
 Further discussion of the base line is presented later in this
 section.
 Dry weather was responsible for suspension of grazing on
unirrigated pasture for seven days in August 1955. Cold dam-
age to the pasture during the winter of 1955-56 necessitated re-
moval of animals from the irrigated plots for 35 days. Dry and
cold weather were responsible for a 62-day interruption in graz-
ing of the unirrigated pasture during the winter, and dry weath-
er caused a 28-day suspension in April 1956.
 Severe freezes in December 1956 and January 1957 along
with an epidemic of Stemphylium leaf spot were responsible for
a delay in grazing on the irrigated pasture until February 20.
These factors plus dry weather delayed beginning of grazing
on the unirrigated pasture until April 1957.
 In determining the acreage of pasture to grow, both the level
and uniformity of supply of total digestible nutrients it will
provide are important. These factors also will influence the
amounts of supplemental feeds the herd will need and the quanti-
ty of surplus forage likely to occur. Each person must assess
these factors in relationship to his resources in arriving at the
acreage of pasture to plant. To illustrate the principle involved