QUALITA’ DELLA BIOMASSA E RALAZIONI FRA PARAMETRI QUALITATIVI E
BIOMETRICI
Roberta Rossi1*, Rocco Bochicchio2, Rosanna Labella2, Mariana Amato2
1 Consiglio per la Ricerca in Agricoltura e l’Analisi dell’Economia Agraria- Centro di Ricerca Zootecnia e Acquacoltura (CREA-ZA) - sede di Bella, via
Appia, Bella (PZ) , Italy
2 Scuola di Scienze Agrarie, Forestali, Alimentari e Ambientali (SAFE) , Università degli Studi della Basilicata (UNIBAS), viale dell’Ateneo Lucano, PZ,
Italy
Abstract
Chia seeds are considered one of the richest source of omega-3 but recently the interest has shifted to the whole plant. Chia leaves are rich in beneficial long-chain fatty acids and flavonoids and have themselves a market potential as a functional food or feed ingredient. Little is known on crop response to agronomic management and much less is available on herbage yield and quality . These preliminary data indicate that forage quality is affected by plant density, is high at early vegetative stages and decreases during the growing season and is higher at low plant density. Protein content drops from 18% at early vegetative stage to the 9% of early flowering while fiber content (ADF) increases from 25% to 37% on average from sowing to flowering. Proteins and lipids are significantly affected by sowing density at late vegetative and early flowering stages (P-value < 0.05). Chia forage shows a low proportion of palmitic and stearic acids and a high proportion of alpha- linoleic acid especially at early vegetative stage (max value 623 g fatty acid kg-1 Total Fatty acid), and a favorable omega-3
to omega-6 FA ratio that during the growing season ranges from 6 to 4. Leaf-to-stem ratio declines exponentially with yield (R2= 0.87, P-value< 0.05) and it increases with N content following a power relationship (R2=0.64, P-value< 0.05). Crop height is inversely related to polyunsaturated:total fatty acid ratio and is positively and linearly related to fiber content. These linear relationships differ for the two plant densities being steeper at high plant density. Crop height, LAI and leaf-to- stem ratio are useful indicators of forage quality variation during the growing season and can be used to individuate optimal cutting windows
Keywords: Chia (Salvia hispanica L.); forage quality, omega-3; functional feed; allometric relationships Parole chiave: Chia (Salvia hispanica L.); qualità del foraggio; foraggi funzionali; relazioni allometriche Introduction
In recent years a special attention has been given by dairy industries in altering milk fatty acid (FA) composition by maximizing the content of long-chain polyunsaturated fatty acids (PUFA) such as omega-3 and omega-7 FA (Dewhurst et al., 2003). These bioactive compounds play a key role in reducing cardiovascular risk and increase milk anti-carcinogenic properties (Williams, 2000). Ruminants cannot synthesise long-chain FA endogenously so their content in milk depends on their proportion in ingested feed and is mediated by rumen bio-hydrogenation processes (Witkowska et al., 2008). The use of farm-grown forages represents as a low-cost sustainable approach for modifying milk lipids and at the same time reducing the purchase of expensive formulates (Dewhurst et al., 2006). Chia (Salvia hispanica L.) seeds are considered the richest botanical source of omega-3 (Ayerza, 2009). Chia seeds have been used as feed supplements to improve the fatty acid composition of meat (Ayerza et al., 2002), eggs (Ayerza and Coates, 1998) and milk (Ayerza and Coates, 2006) with no adverse effects on sensory attributes. Despite the fact that much work has been undertaken on seeds, Chia vegetative parts are also of great interest. Chia leaf essential oils show potential for their flavoring and fragrance value (Ahmed et al., 1994). Peiretti and Gai (2009) reported for the first time Chia whole plant fatty acid profile and forage gross properties under uniform agronomic management. Chia forage showed potential for large scale ensiling (Peiretti, 2010). The interest in Chia whole plant is also supported by the high biomass yield. Bochicchio et al. (2015) tested the influence of agronomic management on biomass and seed yield of commercial varieties grown in Mediterranean Europe and reported values up to 8.77 t ha-1 of total dry mass at flowering under non-limiting irrigation. These authors suggested the high biomass and leaf
production during the growing season can be exploited for forage uses, in fact since commercially available varieties are short-day flowering when cultivated at Mediterranean Europe latitude require relatively long growth cycles for flowering which allow the plant to achieve a remarkable size. Chia leaves are also an interesting source of flavonoids, such as
quercetin, common in Salvia species and of uncommon flavonoids (acetyl vitexin and acetyl orientin) showing potential as a functional ingredient (Amato et al., 2015). From the traditional growing areas of Mexico and Guatemala, Chia cultivation is rapidly spreading oversea and therefore there is a growing need to develop appropriate agronomic management techniques for maximizing yield and quality in different environments and latitudes and for different market objectives. In this work we analysed the effects of plant density and nitrogen fertilization on chia forage quality and FA profile and analysed the relationships between forage quality and biometric parameters. Allometric relationships between quality parameters and fast measurable crop biometric attributes such as LAI, height, leaf- to- stem ratio can be used to refine agronomic management strategies and help individuating optimal cutting windows for obtaining a Chia forage with a high digestibility and reach in health-promoting polyunsaturated fatty acids.
Materials and Methods
The experiment was conducted in 2013 and 2014 at Masserie Saraceno (Atella - PZ, Southern Italy, Lat. N 40° 51’ 37.59”, Long. E 15° 38’ 49.43”) on a Luvi-vertic Phaeozem (Iuss working group, 2006). Soil texture and weather parameters were described by Bochicchio et al. (2015). A black chia (Salvia hispanica L.) commercial seed available at Eichenhain (Hofgeismar - DE) was sown on 21/06/2013 and grown with non-limiting water supply. Drip irrigation amounted to 711.3 m3 ha-1. The soil was amended in June 2013 with 25 t ha–1 of the solid fraction of biogas digested materials with the following characteristics: dry matter 8.5%; carbon 20.4 kg t–1; nitrogen (N) 2.8 kg t–1; ammonium (N-NH4) 0.6 kg t–1; P
2O5
1.4 kg t–1; K
2O 2.5 kg t–1.Sowing density (D1=125 plants m-2 and 8 plants m-2) and top-dressing nitrogen fertilization (0 and
20 kg ha-1 at 49 DAS) were tested within a split-plot design replicated 2 times . Samples were taken in each plot at different stages: EV (early vegetative stage, 44 DAS), LV (late vegetative stage, 77 DAS) and EF (early flowering, 103 DAS) and crop height and LAI were measured manually. For chemical analyses samples were dried and ground to pass through a 1 mm screen and analysed for the following determinations: total N content by Kjeldahl method, ash content by ignition to 550 ◦C, and ether extract by Soxlet method were determined as described in AOAC 963.15 (1990). Acid detergent fibre and neutral detergent fibre were determined as described by Van Soest et al. (1991) expressed exclusive of residual ash. Lignin was determined by solubilization of cellulose with sulphuric acid as described by Robertson and Van Soest (1981). Lipid extraction was performed on freeze-dried samples according to Hara and Radin (1978). Fatty acids were analysed as their methyl esters (FAME). The analysis was carried out by gas chromatography, using a a Varian Star 3400 CX GC (Varian-Agilent, Milan, Italy), equipped with a SLB®-IL111 Capillary GC Column (100 m × 0.25 mm × 0.20 µm) (Sigma- Aldrich, Milan, Italy). The separation was carried out at 90/240 °C with helium as carrier gas and using a flame ionization detector (FID) at 300 °C. FAMEs were identified by comparison of retention times with FAME standard mixture under the same conditions (Supelco 37 Component FAME Mix analytical standard, Sigma-Aldrich, Milan, Italy). Data were subjected to regression analysis and to a mixed effects ANOVA with random effects for both block and nitrogen top- dressing (Pinheiro and Bates, 2000) .
Results and Discussion
Forage quality (reported in table 1) decreases during the growing season but mostly at high plant density that at all crop stages showed a lower protein and lipids content, the opposite occurs with fibre content, data are consistent with literature (Peiretti and Gai, 2009). Protein content was significantly affected by top-dressing fertilization, a significant interaction with density was found at late vegetative stage (LV), where fertilization increased the difference in protein content between D1 and D4. Chia shows a low proportion of saturated fatty acids and it is rich in polyunsaturated fatty acids (PUFA), Alpha-linolenic acid (ALA) was the most abundant FA reaching the maximum concentration of 62 g 100g FA-1 at early
vegetative stages, and it is followed by linoleic acid whose proportion slightly increased during the growing season (max value 12 g 100 g FA-1 at EF) and by the monounsaturated (MUFA) oleic acid. The proportion of ALA remains relatively
high during the growing season. Even averaging only values from late vegetative stage to flowering (53 g 100g FA-1), it is higher than in many forbs and legumes (Elgersma et al., 2013). The percentage of the other fatty acids increased during the growing season, but the omega3:omega 6 ratio remains relatively high ranging from 6 (EV) to 4 (EF) and so is the ratio PUFA:MUFA.
Table 1. Chemical composition (g kg-1 DM basis) of Chia forage (Top) and Fatty Acid profile (g Fatty acid kg-1 Total FA)
measured at three growth stages: 44 Days after sowing (DAS) corresponding to early vegetative stage (EV), 77 DAS late
vegetative (LV) and 103 DAS early flowering and at two sowing densities (D1 = 125 plants m-2 and D4 = 8 plants m-2)
Tabella 1. Composizione chimica (g kg-1 DM basis) del foraggio di Chia (in alto) e profilo degli acidi grassi (g acidi grassi
kg-1 Totale acidi grassi) (in basso) misurati in tre stadi di crescita: 44 giorni dopo la semina (DAS) che corrisponde alla
fase denominata fase vegetativa precoce (EV); 77 DAS fase vegetativa tardiva (LV) e 103 DAS inizio fioritura (EF) e a due
densità di semina (D1 = 125 piante al m-2 e D4 = 8 piante al m-2)
Gross quality g kg-1 DM
Density Stage lipids PC ash NDF ADF Lignin
D 1 EV 23,35 b 167,60 141,40 414,70 a 253,70 59,09 b D 4 EV 33,48 a 184,03 148,78 380,85 b 253,10 59,16 a average 28,41 175,81 145,09 397,78 253,40 59,13 D 1 LV 19,18 b 107,78 b 98,38 429,53 b 341,33 a 75,09 a D 4 LV 24,65 a 125,73 a 98,48 468,53 a 282,85 b 62,04 b average 21,91 116,75 98,43 449,03 312,09 68,56 D 1 EF 17,13 81,40 b 67,65 b 434,33 B 394,73 a 85,00 D 4 EF 21,75 99,63 a 69,00 a 472,10 A 337,73 b 74,88 average 19,44 90,51 68,33 453,21 366,23 79,94
Fatty acids g fatty acid kg-1 Total Fatty acid
Density Stage C16 C18 c18:1n–9 C18:2n–6 C18:3n–3 D 1 EV 94,74 b 19,43 17,75 111,84 630,62 D 4 EV 98,29 a 20,50 19,56 108,24 615,34 average 96,52 19,96 18,66 110,04 622,98 D 1 LV 118,45 26,25 28,06 122,52 a 581,73 a D 4 LV 121,29 28,25 28,28 119,03 b 571,77 b average 119,87 27,25 28,17 120,78 576,75 D 1 EF 124,80 41,00 47,25 125,29 478,11 D 4 EF 123,78 41,12 44,76 124,55 475,82 average 124,29 41,06 46,00 124,92 476,96
Allometric relationships are displayed in Figure 1. Leaf-to-stem ration declined exponentially with yield
(y= exp (3.23-3.71x ; R2= 0.87, all parameters are significant at P < 0.05) and is increased with increasing N content
following a power low growth curve (y=9.52 x1.58; R2=0.64, all parameters are significant at P < 0.05). Crop height was
related to many important quality parameters such as N and ADF though the relationship differs for the two densities being steeper at low density. LAI can be used as a predictor of leaf-to-stem ratio that can be considered a synthetic indicator of forage quality . Crop height was linearly and negatively related to PUFA proportion and inversely and non-linearly related to leaf-to-stem ratio.
Figure 1 Relationships between Chia forage quality and crop biometry during the growing season and at different plant
densities (D1= 125 plants m-2 vs D4= 8 plants m-2). Top from left to right: Leaf –to-Stem ratio (LSratio) vs Total Dry
weight (TDW) (Mg ha-1) = Total dry weight; LSratio vs Protein content (N) % (DM); LSratio vs Leaf Area Index (LAI).
Middle from left to right: LSratio vs crop height (H) (cm); PUFA (g PUFA Kg FA-1) vs H (cm); Omega-3:Omega-6 FA
ratio vs protein content (N) (% DM) . Bottom from left to right: Acid Detergent Fiber (ADF) % DM vs H (cm) ; ADF (% DM) vs LAI; Protein content (N) % DM vs H (cm).
Figure 2 Relazione fra i parametri qualitativi del foraggio di Chia e parametri biometrici misurati nel corso del ciclo
vegetativo e in corrispondenza di diverse densità di semina (D1= 125 piante al m-2 vs D4 = 8 piante al m-2). In alto da
sinistra verso destra: il rapporto stelo foglie (LSratio) vs la resa (TDW= biomassa secca totale (Mg ha-1); LSratio vs il
contenuto di proteine (N) (% di sostanza secca); LSratio vs indice di area fogliare (LAI). Al centro da sinistra verso destra;
LSratio vs altezza piante (H) (cm); PUFA (g PUFA Kg FA-1) vs H (cm); rapporto Omega-3:Omega-6 FA vs contenuto
Proteico (N) (% DM) . In basso da sinistra vs destra: Fibra acido detersa (ADF) % DM vs H (cm); ADF (% DM) vs LAI; contenuto proteico (N) % DM vs H (cm).
Maximum forage quality is obtained at very early vegetative stage and tends to be higher at low plant density. At low plant density a cutting window between 44 and 77 DAS which would roughly correspond to a crop height of about 50 cm would allow to harvest about 1.4 tons ha-1 (DM basis) of forage with approximately 17% of protein, an ADF content below 25% and a favourable omega-3:omega-6 ratio. At high planting density protein content and digestibility decline rapidly as crop height increases therefore the optimal cutting window tends to be narrower.
Conclusions
Chia forage shows a high proportion of omega-3 FA and a favourable omega-3 to omega-6 ratio especially at early vegetative stages. Forage quality is influenced by sowing density and declines at flowering. The choice of the optimal plant density is a trade-off between the necessity of weed-control the costs of seeds and machinery requirements, these preliminary data, however, indicate that a better forage quality can be obtained at low plant density especially if harvesting is delayed to late vegetative stages. Protein and fibre content correlate with crops architectural parameters (height, LAI and leaf-to-stem ratio) that can be measured rapidly and at very low cost during the growing season. Validation of these allometric relationships over multiple years and genotypes can help selecting a few fast measuring indicators for crop
monitoring that can be used to tune management practices aimed at obtaining a forage with a high digestibility and rich in health-promoting fatty acids.
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