Changes of crude protein content in lucerne plant during the first three vegetation cycles

Investigation was performed to observe the changes of crude protein (CP) content in lucerne plant during the first three vegetation cycles within one vegetation season, with the aim to optimize the lucerne utilization in ruminant nutrition. A total of 143 samples were collected from 7 April 2010 (the start of the spring vegetation) to 9 August 2010 (the end of the third vegetation cycle). The sampling was done by cutting a randomly chosen area of 0.1 m2. Crude protein (CP, expressed in dry matter) was analyzed in all samples with standard Kjeldahl procedure. Samples were collected in all stages of the three vegetation cycles, from the early vegetation to the ripe pod phase. There were large differences in plant protein content changes during different vegetation cycles. During the first vegetation cycle, which had the highest yield of plant green mass, there was a sudden drop in the protein content that was coinciding with optimal cutting moment. In absolute values, this drop was more than 8 percent points of CP during the 10-day period. Second and third vegetation cycles had slower and more uniform decreases in CP content during vegetation. Postponing the cutting moment in order to obtain higher yield, during the first vegetation cycle may lead to radical decrease of the nutritive value in lucerne. Adequate and rapid evaluation of the right moment for lucerne cutting is very important in order to obtain quality forage rich in protein