Citation: Honfy, V.; Pödör, Z.; Keser˝ u, Z.; Rásó, J.; Ábri, T.; Borovics, A. The Effect of Tree Spacing on Yields of Alley Cropping Systems—A Case Study from Hungary. Plants 2023, 12, 595. https://doi.org/10.3390/ plants12030595 Academic Editors: Muhammad Ali Raza and Wenyu Yang Received: 29 December 2022 Revised: 24 January 2023 Accepted: 26 January 2023 Published: 29 January 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). plants Article The Effect of Tree Spacing on Yields of Alley Cropping Systems—A Case Study from Hungary Veronika Honfy 1, *, Zoltán Pödör 2 , Zsolt Keser ˝ u 1 ,János Rásó 1 , Tamás Ábri 1 and Attila Borovics 3 1 Department of Plantation Forestry, Forest Research Institute, University of Sopron, Farkassziget 3, H-4150 Püspökladány, Hungary 2 Faculty of Informatics, Eötvös Loránd University, Pázmány Péter str. 1/C, H-1117 Budapest, Hungary 3 Department of Tree Breeding, Forest Research Institute, University of Sopron, Várkerület 30/A, H-9400 Sárvár, Hungary * Correspondence: honfy.veronika@uni-sopron.hu; Tel.: +36-701975349 Abstract: Alley cropping is a specific agroforestry system, which is regarded as sustainable land use management, that could play a crucial role in climate change adaptation and mitigation. Despite its appealing attributes, farmers’ up-take of the system is slow in temperate regions. This study aims to contribute to scaling-up agroforestry through a case study in Hungary and to help to design productive alley cropping systems. We investigated which tree planting pattern of black locust (Robinia pseudoacacia L.) results in the most productive alley cropping system when intercropped with triticale (x Triticosecale W.) by statistically analysing the yields of the intercrop and of the trees in nine different layouts and by calculating land equivalent ratios (LER). There was significant difference between the treatments both in triticale and black locust yields. The more trees planted on a hectare, the higher the volume of the stand, and the less yield of triticale was observed, although the latter correlation was weak and in some cases the triticale was more productive between the trees compared with sole crop control. Eight out of nine treatments had favourable LER (0.94–1.35) when the trees were five years old. Black locust and triticale seem to be a good combination for productive alley cropping systems. Keywords: temperate agroforestry; silvoarable; cereal; spatial arrangement of trees; dendromass; land equivalent ratio 1. Introduction The main objective of this study is to provide data on yields of innovative alley crop- ping systems to contribute to scaling up agroforestry in Hungary and in temperate regions. Agroforestry systems—such as alley cropping—provide economic, social and environmen- tal benefits as compared with conventional farming systems. Relevance of agroforestry research becomes tangible when considering that more than 40% of the world’s agricultural land has over 10% tree cover [1]. Agroforestry is defined as a sustainable land use practice, where woody perennials are purposely grown with other crops and/or are combined with livestock or with other agricultural production, in some form of spatial arrangement or temporal sequence for economic and/or ecological benefits. Alley cropping is a specific type of agroforestry/intercropping system combining fruit, nut, or high-value timber pro- duction with crop production in between the tree rows, but it can also be combined with livestock. Trees provide shelter to crops and animals and shade against the sun, the hail and the wind. In the meantime, competition for resources may take place, such as for the nutrients, water and light, which can result in a substantial decrease in the yields, as is often recorded in intercropping and in some research conducted on alley cropping systems [2–4]. From the point of forestry, non-stand-forming tree species which bare valuable wood or fruits can play a role [5]. Many environmental challenges can be addressed by planting trees into the farm or landscape, as they protect soil and water, improve nutrient cycles and Plants 2023, 12, 595. https://doi.org/10.3390/plants12030595 https://www.mdpi.com/journal/plants