RESPONSE OF SOLAR RADIATION BIOCONVERSION ON MEDICAGO ... · and Mihaela). The cultivars were sown in a Latin rectangle design with four replicates. For ensiling, wilted Medicago

RESPONSE OF SOLAR RADIATION BIOCONVERSION

ON MEDICAGO SATIVA L. SILAGE POTENTIAL

D. DUNEA1, N. DINCA2*, C. RADULESCU3,4*, C. MIHAESCU5, I.D. DULAMA4, S. TEODORESCU4

1 Valahia University of Targoviste, Faculty of Environmental Engineering and Food Sciences, 13 Sinaia Alley, 130004 Targoviste, Romania, E-mail: [email protected];

2 University of Agronomic Sciences and Veterinary Medicine of Bucharest, 59 Marasti Blvd, District 1, Bucharest, Romania, E-mail: [email protected];

3 Valahia University of Targoviste, Faculty of Sciences and Arts, 13 Sinaia Alley, 130004 Targoviste, Romania, E-mail: [email protected];

4 Valahia University of Targoviste, Institute of Multidisciplinary Research for Science and Technology, 13 Sinaia Alley, 130004 Targoviste, Romania, E-mail: [email protected],

[email protected]; 5 University of Pitesti, 1 Targu din Vale Street, Pitesti, Romania.

*Corresponding authors: [email protected]; [email protected].

Received October 31, 2017

Abstract. 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 ¼ 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-1 m-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 ¼ 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.

Key words: biometeorology, radiation use efficiency, Medicago sativa, crude

protein, relative feed value, alfalfa.

Romanian Journal of Physics 63, 803 (2018)

mailto:[email protected]:[email protected]

Article no. 803 D. Dunea et al. 2

1. INTRODUCTION

Medicago sativa L. is widely considered “the queen of forage crops”

because of its ecological plasticity, fodder quality, resistance to drought, important

break crop in the rotation, and symbiotic fixation of nitrogen in soil. Medicago

sativa is estimated to fix 83–594 kg N ha-1

yr-1

[1]. Crop yield varies with climate

and length of total growing period. Good yields after the first year are in the range

of 2 to 2.5 tons/ha per cut (hay with 10–15% moisture) of about 25 to 30 day

cutting interval [2]. It has valuable fodder properties due to its high content of

proteins, vitamins and minerals. Traditionally, Medicago sativa is preserved as hay,

but the process of obtaining the hay is influenced by the weather conditions and

also delays the regrowth period if the harvested material is not removed from the

field. Wilting is usually performed after harvesting to increase DM content and

decrease the growth of clostridial bacteria [3]. The weather pattern for a growing

season, especially temperature-induced lignification of the neutral detergent fiber

(NDF) and leaf loss from damaging rains can dramatically change the NDF level,

crude protein content or digestibility of the forage even though the fiber content

can remain relatively stable [4].

Furthermore, the hay production is characterized by significant loses e.g.,

21% from dry matter (DM), 28% from crude protein (CP) and up to 40% from the

weight of leaves [5]. Such loses also affects significantly the nutritional quality.

Silage is an alternative method to retain the forage quality. The assessment of

silage quality is typically based on determining the fermentation qualities and

changes in microbial compositions. The most common indicators include the silage

DM weight and content, water-soluble carbohydrate concentration, and target

bacterial counts [6]. In the mass of ensiled fodder, there is mainly lactic

fermentation, but also secondary fermentations: acetic, butyric and alcoholic may

occur. The predominance of one or the other depends on several factors, of which a

decisive role is the presence or absence of oxygen, the reaction of the environment

and the content of the silage plants in soluble carbohydrates. Lactic fermentation

has the main importance because it leads to the accumulation of lactic acid, a

preservative, on which depends the quality of the silage. Lactic fermentation is

produced by lactic bacteria (e.g., Streptococcus, Leuconostoc, Lactobacillus,

Pediococcus), which convert carbohydrates to lactic acid and small amounts of

acetic, succinic, formic and propionic acid.

Lactic bacteria support a stronger acidic environment than butyric bacteria,

i.e., pH less than 4.5. At these pH values, butyric fermentation bacteria as well as

other bacteria leading to unwanted secondary fermentations cease their activity.

The mold develops to the reaction of the medium corresponding to a pH between

1.2 and 1.8, but does not support anaerobiosis [7].

An important role has the content of soluble carbohydrates. Thus, perennial

grasses, harvested in the optimum stage for silage, have soluble carbohydrate

3 Response of solar radiation bioconversion on Medicago Sativa L. silage potential Article no. 803

content up to 20%, depending on the species and cropping technology, while in

legumes, the proportion of soluble carbohydrates is only 9–10% of the DM [8],

which is insufficient to achieve the required amount of lactic acid.

Medicago sativa can be preserved in silage with some difficulties due to its

low content of fermentable sugars requiring extra carbohydrates and lactic acid

bacteria (LAB)-containing additives for proper fermentation [9]. The fermentation

of Medicago sativa silage with LAB additives results in a decrease in pH due to the

production of organic acids during the process [6]. Growth of Clostridia increases

proteolysis and butyric acid in legume silages [10, 11]. Butyric acid is considered

to be responsible for reducing silage palatability.

In Romania, the traditional method uses the direct harvest and silage of

harvested material after a preliminary chopping and mixing with green maize [12],

Sudan grass, straws and preservatives [7]. In these conditions, the fermentation

process runs slow because of the low content of soluble sugars (7–8%). To support

the fermentation process, the lowering of the humidity is required up to 55–65%

for the harvested material, followed by its chopping and depositing in silages [5].

Later on, the stored material must be compacted to obtain the anaerobic conditions

that favor the multiplication of lactic ferments. Hence, the fodder conservation is

realized in short time and loses (especially the percentage of leaves) are

significantly diminished. The butyric fermentation may occur at > 65% humidity,

while a humidity < 55% favors aerobic fermentation because the compaction is

hindered.

DM accumulation and allocation in morphological organs as well as the

qualitative parameters of forage are directly correlated to the amount of intercepted

photosynthetically active radiation (PARi) by the canopy of species [13]. Radiation

use efficiency (RUE) is a key indicator of biological efficiency of a species

regarding the conversion of light in DM (b) [14]. In Medicago sativa, Justes et al. [15] found a RUE of 1.72 g DM MJ

−1 irrespective of sowing date (spring or

summer), and Allirand [16] 1.76 g DM MJ−1

, respectively. Brown et al. [17]

showed that estimated radiation use efficiency (RUE) in Medicago sativa had a

distinct seasonal pattern, increasing from 0.80 g DM MJ-1

in early spring to

1.60 g DM MJ-1

in late summer before decreasing to 0.80 g DM MJ-1

in late

autumn. In dry and full sunlight conditions, Varella [18] observed mean RUEs over

the experimental period of 1.06 g MJ-1

. Stanciu et al. [19] found RUEs of

1.82 g DM MJ-1

m-2

for orchard grass in mixture with Medicago sativa. Generally,

mixtures of perennial grasses with Medicago sativa provided increased RUEs

during growth seasons due to a better interception of solar radiation in the

heterogeneous canopy [20].

Consequently, a higher quantity of light and a better cropping management

including proper hay and silage production are expected to increase RUEs and

improve forage quality. Solar cycle, nebulosity and climate change are independent

factors that are determining PAR availability and thus, Medicago sativa growth. In


this context, the objective of the study was to assess the solar radiation

bioconversion to DM accumulation and silage quality in Medicago sativa during

three years of cropping in Targoviste Piedmont Plain, Romania. Farmers may use

this type of information to maximize the maintenance of the nutritional quality for

obtained fodders in the context of climate change.

2. MATERIALS AND METHODS

The experiments were carried out in Targoviste Piedmont Plain, Romania

(N44°46¹.905, E25°43¹.045, 179-m altitude) between 2012 and 2014 on

pseudogleic brown alluvial soil using two Romanian synthetic cultivars of

Medicago sativa (i.e., Roxana and Mihaela species) developed at NARDI Fundulea

[21]. The cultivars were sown in a Latin rectangle design with four replicates. The

plants were given nitrogen fertilizer in all experimental variants at one rate (25 kg

N ha-1

) to support crop establishment and avoid nutrient limiting growth. Irrigation

was not applied to comply with the common cropping practices used by farmers in

the region. Three cutting cycles were performed each year according to the

recommended phenophases for Medicago sativa harvesting [5] i.e., first cutting

cycle: at the beginning of flowering stage; second: +7 weeks from the first cut;

third cutting: +6 weeks after second cutting.

Samples were collected before each cutting cycle using a quadrate of 50

50 cm in two points of each variant and each repetition to determine DM

accumulation (g·m-2

). The continuous energetic fluxes of solar radiation at the location were determined using a PAR Quantum Sensor (range = 0–2000 µmol m

-2s

-1) connected to a data logger. Meteorological parameters at the experimental

field were acquired using a Delta-T Devices automatic weather station (Table 1).

For ensiling, wilted Medicago sativa from both cultivars (50–60% moisture)

and ¼ green maize leaves were chopped at 2–3 cm, mixed together and compacted

in 2-L containers with gas release valve for 35 days. The silage samples (2 for each

replicate; n = 16) were made only in the first cropping cycle of each year.

The containers were opened on 36 day for determination of pH, DM, CP,

and total acids content. The silage pH was determined using a WTW pH-meter.

Molecular identification of chemical functional groups of organic/inorganic

compounds (i.e. forage chemical composition CP, Acid Detergent Fiber – ADF,

Neutral Detergent Fiber – NDF, and mineral content) was performed by

Attenuated Total Reflection – Fourier Transform Infrared Spectrometry (ATR-

FTIR) using Vertex 80v spectrometer (Bruker), which absorbs infrared radiation in

350–8000 cm-1

range, equipped with diamond attenuated total reflection accessory,

as well as with Hyperion IR microscope [22–26].


Table 1

Meteorological parameters recorded during the experiment in Targoviste Piedmont Plain

between 2012 and 2014 (annual averages)

Meteorological parameter 2012 2013 2014 Average Coeff. of

var.(%)

Temperature (C) 10.9 8.1 10.8 9.9 16

Relative humidity (mm) 71.4 78.3 79.8 76.5 5.9

Sum of precipitations (mm) 612 553 1039 734.7 36.1

Days without precipitations 308 235 300 281 14.2

Global radiation (MJ/m2/day) 13.9 14.2 12.9 13.7 5

Total global radiation (MJ/m2/yr) 5110 5161 4892 5054.3 2.8

ADF is the fibrous component representing the least digestible fiber portion

of forage, while NDF is an estimate of the total fiber components (lignin,

cellulose, hemicellulose, tannins, cutins and silica).

The organic acids (i.e. lactic, acetic and butyric) were determined by gas

chromatography (GC) method [27]. Analyses were performed with an Agilent

6890N GC Chromatograph equipped with Flame Ionization Detector (FID) and

Autosampler. A J&W DB-624UI GC column, 30 m × 0.32 mm, 1.8 µm was held at

the temperature of 260 ºC. Hydrogen (38 cm/s) was used as carrier gas. Injection

volume was 1.0 mL/min, constant flow mode; n-propanol was used as internal

standard.

Nutritive value of forages depends on their DM digestibility and voluntary

DM intake. Relative feed value (RFV), which is a widely accepted forage quality

index that combines the estimates for forage digestibility and intake into a single

number, was computed. RFV for legumes and legumes mixtures is calculated from

estimation of ADF and NDF [28], as follows:

RFV = (65.5+0.975 ADF–0.0277 ADF2) (39.0+2.68 NDF–0.041 NDF

2) 0.025

The indicators of fodder quality were correlated with the amount of available

PAR during various crop cycles using Pearson correlation. Statistical analysis was

carried out using Statgraphics (StatPoint Inc., 2005) [29]. Significance between

individual means was identified using Least Significant Difference (LSD) multiple

comparison test. Mean differences were considered significant at p < 0.05.

Regarding the climatic variability during experiment, the year 2013 recorded

the lowest annual average temperature (8.1 C) with more than 2.5 C lower

compared to 2012 and 2014. The year 2012 showed the highest amplitude of

temperature regime, while year 2014 was characterized by the significant amount

of annual precipitations and increased relative humidity.

The highest amount of solar radiation was recorded in 2013, the second year

of Medicago sativa cropping and the lowest in 2014, which was a year with

increased nebulosity and rainfalls exceeding the multiannual average. Global


radiation showed the lowest variance, while the sum of precipitations reached the

highest coefficient of variation (36.1%).

3. RESULTS AND DISCUSSION

3.1. SOLAR RADIATION BIOCONVERSION TO DRY MATTER IN MEDICAGO SATIVA

Medicago sativa L. is a perennial crop that produces its highest yields during

the second year of growth [2]. However, in this experiment the highest yields were

obtained in the third year of cropping mainly due to the higher amounts of

precipitations that were optimally distributed during the cropping cycles of year

2014.

Although it is resistant to drought, Medicago sativa provides profitable yields

only in regions where the annual precipitations sum exceeds 500 mm, which are

well distributed during the growth season [9]. Medicago sativa required 750–

800 C for each cutting cycle. Temperatures > 35 C occurred in the first cycle of

year 2013 reducing the yield and corresponding RUE.

Table 2 shows the RUEs recorded during the field experiment. Mihaela

cultivar showed higher RUEs than Roxana excepting the 3rd cutting in 2012. No

statistical difference (p > 0.05) was observed between cultivars.

Mihaela cultivar showed an improved bioconversion of solar radiation to DM

throughout growth seasons recording RUEs of 1.6–1.77 g MJ-1

m-2

in the 1st cycle,

1.4–1.66 g MJ-1

m-2

in the second cycle, and 0.78–1.02 g MJ-1

m-2

in the third

cycle. Roxana cultivar provided similar RUEs i.e., 1.47–1.74 g MJ-1

m-2

in the 1st

cycle, 1.27–1.61g MJ-1

m-2

in the second cycle, and 0.79–0.98 g MJ-1

m-2

in the

third cycle. The similar responses occurred because the cultivars were obtained

from the recombination of foreign and Romanian germplasm [21]. Both cultivars

presented closed canopies, rapid spring growth, faster regrowth after cutting, good

resistance to common diseases occurring in Romania, and improved winter

hardiness. RUE had a reduced variance between years in the same cropping cycle,

the highest being observed for the 3rd

cutting cycle (Coeff. of var. = 13.8%).

The main factor determining the Medicago sativa growth, including the rate of

biomass accumulation, is the amount of carbon assimilated through photosynthesis,

which in turn is dependent on the amount of light intercepted by the canopy. Once

carbon is assimilated though photosynthesis, biomass can be partitioned to

aboveground morphological components (leaves and stems) or perennial

belowground organs (crowns and roots) [30]. The canopy architecture of Medicago

sativa provides efficient light capture because of the leaf area distribution of flat

leaves in the lower layers of the canopy and vertical leaves in the top [31].

Medicago sativa detains an optimal light extinction coefficient per unit of leaf area

between 0.8 and 0.9.


Table 2

Radiation use efficiency (g MJ-1 m-2) of Medicago sativa cultivars grown

in Targoviste Piedmont Plain, Romania between 2012 and 2014 (three cutting cycles/year)

Cultivar 2012 2013 2014 Average Coeff. of var.(%)

Roxana

1st cutting 1.51 1.47 1.74 1.6 9.3

2nd cutting 1.33 1.27 1.61 1.4 12.9

3rd cutting 0.84 0.79 0.98 0.9 11.3

Annual average 1.23 1.18 1.45 1.3 11.2

Mihaela

1st cutting 1.61 1.60 1.77 1.7 5.7

2nd cutting 1.47 1.40 1.66 1.5 8.9

3rd cutting 0.78 0.86 1.02 0.9 13.8

Annual average 1.29 1.29 1.48 1.4 8.1

LSD 95% diff. ±0.90 ±0.83 ±0.91 – –

The RUE results of Romanian cultivars were in agreement with data reported

for Medicago sativa in [15, 16]. Moot [31] pointed out that in Medicago sativa,

RUE for total biomass, as a proxy for net canopy photosynthesis, is approximately

1.8 g MJ-1

(total solar radiation). Under water stress, the RUE of a Medicago

sativa-grass mixture was 1.4 g MJ-1

[32]. An increased RUE value does not

necessarily imply an improved quality of the forage because by advancing towards

maturity the proportion of lower quality stem material (lignification) increases and

the overall leaf to stem ratio declines [33]. Leaf/stem ratio is a reliable indicator

regarding the fodder quality in Medicago sativa, but was not determined in this

study.

3.2. SILAGE COMPOSITION AND RELATIONSHIP WITH BIOCONVERSION EFFICIENCY

The quality of herbage in Medicago sativa is directly related to the fraction of

leaf and palatable stem compared with lower quality lignified stem [31].

Traditional hay production determines high loses of leaves due to shaking, which

drops significantly the fodder quality. Furthermore, unfavorable weather conditions

during field drying in rows may compromise the forage yield. Proper ensiling may

maintain the nutritional quality preserving crude protein, minerals and vitamins.

Table 3 shows the silage composition determined for the harvested and ensiled

Medicago sativa material mixed with ¼ maize leaves at the first cycle of each year

of cropping. The DM content was almost constant between years recording a

multiannual average of 30.4%. CP showed a diminishing towards the third year of

cropping with 5% DM. A fodder rich in protein can be obtained from an early

harvesting but this could reduce the longevity of Medicago sativa [9]. In this

experiment, crop aging and later cutting applied in the third year were responsible

for the diminishing of CP and increasing of cellulose content in Romanian


cultivars. After 35 days of ensiling, total acids ranged between 4.9 and 6.8% DM

from 2012 to 2014 first crop cycles showing the highest variance of the tested

variables (Coeff. of var. = 17.3%). This increment suggests that the quality of

fodder has diminished with the crop aging, increasing the concentration of butyric

acid from 0.4 (2012) to 1.5% DM (2014) and acetic acid from 1.3 to 2.6% DM.

Acetic acid is associated with undesirable fermentations, while butyric acid favors

protein degradation, toxin formation, and significant losses of DM and net energy.

Lactic acid bacteria (LAB) utilize water-soluble carbohydrates to produce

lactic acid, which is the primary acid responsible for decreasing the pH in silage

[34]. The concentration of lactic acid remained almost constant (2.7–3.2% DM).

The lowest pH (5.2) was determined in the silage obtained in the third cropping

year, while the maximum was in the first year (5.8). The drop in pH was mainly

determined by the lactic acid formation during fermentation process. Low pH

values are favorable for better preserved and more stable Medicago sativa silages.

However, Medicago sativa has a high buffering capacity compared to maize

requiring increased acid production to lower the pH in Medicago sativa, which is

difficult to obtain. The DM content of the forage can also have major effects on the

ensiling process due to a number of various mechanisms [35]. First, drier silages do

not pack well making difficult to extract all the air from the forage mass. Second,

as DM content increases, growth of LAB is reduced followed by the reduction of

the rate and extent of fermentation (slower acidification process and less total

acids). In this experiment, addition of green maize leaves has increased the fodder

quality, ensiling potential and silage stability.

A very significant inverse correlation was observed between RUE and silage

CP content of each replicate (Pearson r = –0.985; p < 0.001) showing that the

increasing of RUE determines the decreasing of CP content (%DM) of silage

(Fig. 1).

Table 3

Silage composition of Medicago sativa cultivars grown in Targoviste Piedmont Plain mixed with

¼ maize leaves; ensiling was made at the first cycle of each cropping year between 2012 and 2014

after 35 days of fermentation

Year 2012 2013 2014 Average St. Dev. Coeff. of var. (%)

Dry matter – DM (%) 30.2 29.8 31.1 30.4 0.7 2.2

Crude Protein (%DM) 24.6 21.7 19.6 22.0 2.5 11.4

ADF (%DM) 29.7 28.4 26.5 28.2 1.6 5.7

NDF (%DM) 39.1 42.2 44.3 41.9 2.6 6.2

Total acids (%DM) 4.9 5.4 6.8 5.7 1.0 17.3

Lactic acid (%DM) 3.2 2.9 2.7 2.9 0.3 8.6

Acetic acid (%DM) 1.3 1.7 2.6 1.9 0.7 35.7

Butyric acid (%DM) 0.4 0.8 1.5 0.9 0.6 61.9

pH 5.8 5.5 5.2 5.5 0.3 5.5


More efficient bioconversion processes occurring with advancing in maturity

may increase the DM content, but the quality of DM may decrease pointing out

that stand management, especially the selection of harvesting moment is important

for obtaining a favorable balance between forage quantity and quality in Medicago

sativa.

Fig. 1 – Relationship between Radiation Use Efficiency (g MJ-1 m-2) recorded in each replicate

and the crude protein content of resulted silages after 35 days of fermentation; Pearson r = –0.985

(p < 0.001; n = 16).

Fiber fraction digestibility from each crop cycle may differ, because it is

influenced by the air and soil thermal regimes and solar bioconversion at the

specific time of growth and development.

3.3. RELATIVE FEED VALUE OF THE TESTED MEDICAGO SATIVA CULTIVARS

RFV is a widely accepted forage quality index in the marketing of forages.

Higher RFV values indicate higher forage quality. With advancing maturity, plant

structural carbohydrates depicted by the ADF and NDF fractions increase [36].

ADF and NDF, which are fiber fractions, represent the more indigestible parts of

the plant. Consequently, forage digestibility and energy decrease with maturity

[28].


Fig. 2 – Relative feed value of silages resulted from tested Medicago sativa cultivars mixed with ¼

maize leaves after 35 days of fermentation; error bars represent the difference between replicates.

The RFV average of Medicago sativa silages mixed with ¼ maize leaves

ranged between 137.3 (year 2014) and 141.9% (year 2012) confirming the relative

reduction of forage quality with crop aging. Roxana cultivar recorded better RFVs

excepting the second cropping year. Based on RFVs, both cultivars showed good

quality of obtained silages that were superior to the value reported for corn silage-

well eared – 133% [37]. Both cultivars have very good digestibility coefficients

(72–73%) [21].

The current study tried to establish a link between solar radiation

bioconversion and fermentation processes occurring during Medicago sativa

ensiling in view to characterize the ensiling potential and resulted silage quality.

Some limitations of the study were related to the uncertainty determined by the use

of relatively small recipients that might not be suitable to characterize the processes

occurring in high capacity silos. The use of maize leaves in silage formation can

determine difficulties on large-scale farm operations. Consequently, proper grass –

Medicago sativa mixtures may replace the use of maize leaves [38]. RFV index has

some limitations because at the same RFV value, differences in the digestibility of

the fiber fraction can result in a difference in animal performance. RFV cannot

account this situation and other indices might be more suitable (e.g., Relative

Forage Quality [36]).

Future research directions will focus on finding the most appropriate

Medicago sativa – grass mixture in terms of ensiling potential involving a higher

number of Medicago sativa cultivars from various breeders adapted to the eco-

climatic conditions of the study region and variations of the harvesting moment in


the first cropping cycle of growth seasons. Future experiments will consider the use

of homofermentative LAB additives and other effective silage inoculants (e.g.,

buffered propionic acid-based additives [35]) because the inoculation is expected to

lower pH and ammonia-N, and to improve the lactic/acetic acids ratio.

4. CONCLUSIONS

Silage making may maximize the preservation of original valuable nutrients

in the forage crop for later use as fodder. Ensiling fermentation is an unstable

process that is difficult to be controlled and usually leads to nutritional loses

compared to the original harvested material. Dry matter accumulation and some

main qualitative parameters of forage were directly correlated to the amount of

PAR absorbed by the Medicago sativa canopy. The multiannual average of RUEs

in tested cultivars ranged between 1.3 and 1.4 g MJ-1

m-2

. In this experiment, it was

found that increasing of RUE determines the decreasing of CP content (% DM) of

the silage. 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 choice of the harvesting moment is

important for Medicago sativa forage as hay, haylage or silage for insuring the

proper balance between fodder quality and quantity during the whole cropping

cycle. Farmers need timely data regarding the nutritional status of their livestock

and the nutritive value of their forage crops, if they are to apply successfully an

optimized nutritional plan in varying agrometeorological conditions. Consequently,

such experiments may provide key milestones for Medicago sativa stand

management in the context of climate change.

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RESPONSE OF SOLAR RADIATION BIOCONVERSION ON MEDICAGO ... · and Mihaela). The cultivars were sown in a Latin rectangle design with four replicates. For ensiling, wilted Medicago

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