Speaker
Description
Introduction
Sorghum (Sorghum bicolor L. Moench) is a summer crop rainfed in Mediterranean areas for its rusticity and drought tolerance. Hairy vetch (Vicia villosa Roth) is often used as a winter cover crop before cereal cultivation to control weeds, increase soil nitrogen availability, and protect soil and water. Sorghum can also be cultivated with poplar in narrow alleys in agroforestry [1]. However, sorghum is a C4 plant, not tolerant to light reduction [2] and shaded and humid conditions commonly increase the risk of sorghum diseases, such as leaf spot caused by Alternaria alternata (Fr.) Keissl. Anyway, a clear understanding of the effects of agroforestry practices on plant diseases is far from being obtained. Here, we investigated the singular and interactive effects of simulated tree shading and Alternaria infection on grain yield of sorghum cultivated after a vetch cover crop.
Materials and methods
The field experiment was established at Center for Agri-environmental Research “Enrico Avanzi”, University of Pisa, Italy (43.674460 °N, 10.318331 °E) on a loam soil with pH 7.9 and 1.9 % w/w organic matter. Following a randomized complete block design with 4 replications, S. bicolor cv PR89Y79 was grown under full light (FL) or potential light availability reduced by 50% (RL); at flowering, the crop was fully sprayed with A. alternata suspensions (strains A214 and A216) with final concentrations of 0 (A-) or 2 (A+) × 108 CFU mL-1. Vetch was sown in December and mechanically terminated in May using a Crimper Roller, then sorghum was sown on dead mulch. Shading was simulated on half of the plots using plastic slats fixed on iron structures, N-S oriented (2.0 x 2.0 m). Soil water content at two depths (i.e., 0-10 and 10-30 cm) and SPAD, were assessed at three growth stages (i.e., 5-6 leaves unfolded, flowering, and soft dough), and above ground and grain biomass measures were carried out at maturity. Moreover, one month after inoculation, hyperspectral data were collected at both leaf and canopy levels (1 m above the canopy, nadir).
Results
Results show that above-ground biomass of sorghum was the highest in the control without shading and disease, followed by infected plants irrespectively in shaded and full light conditions (Figure). Grain yield of A- more than halved when grown with RL, while it did not differ between FL and RL in A- and A+ plants.
SPAD values decreased more in RL than FL plants when infected than when not-infected (by 27 and 14% respectively). Similarly, a significant shading x disease interaction was observed for four spectral vegetation indices (i.e., color rendering index 1 and 2, normalized difference nitrogen index, and normalized difference lignin index). Soil water content was not significantly chaged by treatments but decreased along the crop cycle and was higher at the lowest profile.
Discussion
A close relationship between sorghum production and light availability was found by [3], but here we revealed that the decreased plant biomass of RL plants was not due to photosynthetic impairments (SPAD values did not drop) but likely to weed pressure (weed biomass was about 130 g m-2) competing for resources. The impacts of agroforestry on diseases have shown context-dependent results [1]; in our research, the lowest biomass and grain production of the shaded and infected plants were consistent with leaf spectral signatures highlighting their potential in assessing crop disturbances by abiotic and/or biotic stress in a timely and cost-effective manner.
This study was carried out within the Agritech National Research Center and received funding from the European Union Next - Generation EU (Piano Nazionale di Ripresa e Resilienza (PNRR) – Missione 4, Componente 2, Investimento 1.4 – D.D. 1032 17/06/2022, CN00000022), and within the Progetto di Ricerca di Ateneo (PRA) “iAgroforestry” 2022/2023.
References
Mantino A., Pecchioni G., Tozzini C. et al. 2023. Agronomic performance of soybean and sorghum in a short rotation poplar coppice alley-cropping system under Mediterranean conditions. Agroforestry Systems 97, 1025–1039.
Reynolds P.E., Simpson J.A., Thevathasan N.V., et al. 2007. Effects of tree competition on corn and soybean photosynthesis, growth, and yield in a temperate tree-based agroforestry intercropping system in southern Ontario, Canada. Ecological Engineering 29:362–371.
Righi C.A., Foltran D.E. 2018. Broomcorn [Sorghum bicolor (L.) Moench] responses to shade: an agroforestry system interface simulation. Agroforestry Systems 92:693–704.
| Keywords | agroforestry; Alternaria alternata (Fr.) Keiss; dead mulch; grain yield; light; Sorghum bicolorr L. Moench. |
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