RESPONSE OF SOLAR RADIATION BIOCONVERSION ON MEDICAGO SATIVA L. SILAGE POTENTIAL

Medicago sativa L is an important perennial plant species, especially in temperate regions, having large requirements for light, heat and water. Dry matter accumulation (DM) and forage qualitative parameters are directly correlated to the amount of photosynthetically active radiation (PAR) intercepted by the canopy. The objective of the study was to assess the solar radiation bioconversion to DM and silage quality in Medicago sativa L during three years of cropping in Targoviste Piedmont Plain, Romania. The experiments were carried out on pseudogleic brown alluvial soil using two Romanian synthetic cultivars (i.e., traditional species Roxana and Mihaela). The cultivars were sown in a Latin rectangle design with four replicates. For ensiling, wilted Medicago sativa and 1/4 green maize leaves were chopped at 2-3 cm, mixed together and compacted in 2-L containers with gas release valve for 35 days. Forage chemical composition of silage was determined using Attenuated Total Reflection - Fourier Transform Infrared Spectrometry (ATR-FTIR). Organic acids were determined by gas chromatography (GC). Relative feed value (RFV) was computed. The multiannual average of Radiation Use Efficiency (RUE) ranged between 1.3 and 1.4 g MJ M--1 (2) in tested cultivars. It was found that increasing of RUE determines the decreasing of CP content (% DM) of the silage (Pearson r = -0.985; p< 0.001). More efficient bioconversion processes may occur with advancing in maturity and crop aging that increase the DM content, but the quality of DM may decrease pointing out that stand management is a key factor to insure optimal nutritional value of the resulted fodder. The RFV average of Medicago sativa silages mixed with 1 /4 maize leaves ranged between 137.3% (year 2014) and 141.9% (year 2012) confirming the relative reduction of forage quality with crop aging. Based on RFVs, both cultivars showed good quality of obtained silages that were superior to the value reported for corn silage-well eared (133%). This type of experiments may provide key milestones for Medicago sativa stand management for maintaining the nutritional quality in the context of climate change.