Perennial ryegrass productivity and nutritive quality as affected by frequency of nitrogen fertilizer addition

In intensive dairy pasture-based systems, split applications of nitrogen (N) use throughout the growth cycle has played an important role in increasing the herbage production and additional forage supply at specific times across the pasture growth season. However, little is known about how the frequency of N applications can modify the crude protein content and their fractions. A mini-sward study was conducted between August 2011 and January 2012 in Valdivia, Chile, to quantify the effect of frequency of N application on herbage yield, growth dynamics and protein fractions in perennial ryegrass swards. A single N rate equivalent of 250 kg N ha(-1) year(-1) of ammonium nitrate (27% N) fertilizer was applied in five patterns based on phyllochron. Thus, the mini-swards were fertilized when they reached 1-2-4-8 phyllochrons, and there was a zero rate of fertilizer application. All mini-swards were defoliated when the ryegrass reached two complete expanded leaves per tiller. The treatments were replicated four times in a completely randomized block design. Defoliations were carried out by harvesting each plot with hand shears to a stubble height of 5 cm. Crude protein fractions were analyzed using the Cornell Carbohydrate and Protein Scheme (CNCPS). The results showed that plants fertilized more frequently (1-2-4 phyllochrons) had a higher (p < 0.001) accumulated herbage mass than plants fertilized every 8 phyllochrons. On the other hand, the fertilization frequency modified the herbage production over the experimental period (p < 0.05). Total crude protein was higher in plants fertilized less frequently, but crude protein fractions were not affected by fertilization frequency.