Competition for Light Affects Alfalfa Biomass Production More Than Its Nutritive Value in an Olive-Based Alley-Cropping System

Alberto Mantino,Cristiano Tozzini,Giorgio Ragaglini,Marcello Mele,Enrico Bonari

doi:10.3390/f12020233

Alberto Mantino, Cristiano Tozzini + Show 3 more

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https://doi.org/10.3390/f12020233

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Abstract

Cropping among trees with perennial legumes is one option for increasing agro-ecosystem services, such as improving the nitrogen supply and increasing soil protection by herbaceous vegetation. Moreover, cropping under the canopy of olive trees should diversify the farm production, compared to the traditional fallow management. Among perennial legumes, alfalfa (Medicago sativa L.) produces abundant biomass under Mediterranean rainfed condition. Based on this, a two-year field experiment was implemented in southern Tuscany in a rainfed olive orchard to test the competition for light effects on alfalfa biomass production and nutritive value. Light availability under the tree canopy was measured by hemispherical photos. In both years, the alfalfa yield of under-canopy varied according to the tree presence. A significant relationship between biomass production and light availability was recorded. The nutritive value of under-canopy alfalfa was similar to that of the open-grown alfalfa. However, same significant differences did however occur, between shaded and sole crop. When differences were found, under-canopy herbage was characterised by a higher content of crude protein and a lower content of fibre with respect to open-grown. In a hilly silvoarable olive orchard, alfalfa biomass accumulation was reduced mainly due to scarce light availability, therefore tree management such as pruning and plantation layout can enhance the herbage productivity. Studying shade tolerant forage legumes in order to enhance the yield and nutritive value of herbage production in rainfed agroforestry systems is essential.

Highlights

In coming years, sustainable agriculture will face the issue of feeding nine billion of people while limiting the environmental risks of cropping practices [1,2]
In this study, the correlation between annual biomass accumulation and available light transmittance was observed in both years, despite a difference of 200 mm of rain fallen during the summer season. These results suggest that ALT affects alfalfa biomass production more than other factors, such as soil water content, as reported by other authors for other herbaceous crops cultivated in agroforestry systems [32,33,35,45]
Biomass reduction of alfalfa cultivated in the alley of an olive orchard mainly depended on light availability and on tree spacing and size

Summary

Introduction

Sustainable agriculture will face the issue of feeding nine billion of people while limiting the environmental risks of cropping practices [1,2]. In Italy, olive tree (Olea europaea L.) is the most widely planted tree crop, covering an area of 1.16 million ha, and often cultivated in agroforestry systems [9,10]. In the hilly areas of central Italy, the soil of olive orchards is usually covered by a low-productive natural vegetation, during winter and spring, while, in summer, farmers perform surface tillage to decrease water competition between herbaceous plants and trees. The tillage of topsoil of the olive orchard alleys can exacerbate the water based erosion risk in hilly areas [15]. The vegetation cover of the soil in the olive orchard alley can enhance the provision of agro-ecosystem services, such as (i) reducing soil erosion, (ii) increasing soil carbon stock, (iii) decreasing nutrient leaching [18], while improving income diversification of farmers

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