In Croatia, farmers are showing increasing interest in establishing walnut orchards for nut production on arable land due to higher anticipated net margins. One way to address the lack of profitability in the initial years when nut yields are low may be to plant arable intercrops. The anticipated impacts of this practice were assessed using a biophysical simulation model (Yield-SAFE) to determine the growth and yield of crops and trees in arable, orchard, and silvoarable systems, and an economic farm model (Farm-SAFE) was used to assess their profitability. The walnut orchard and the intercropped orchard systems were simulated assuming tree densities of 170, 135, and 100 trees ha−1, to determine the profitability and break-even date of the systems. The biophysical simulation predicted a decline in arable intercrop yields over time in all tree density scenarios. However, analysis of productivity of intercropped systems showed that intercropping was more productive than separate arable and walnut production for all tree density scenarios. From financial aspect, the return from intercropping helped to offset some of the initial orchard establishment costs and the arable intercrop remained profitable until the sixth year after tree planting. The modelling predicted that a system with 170 trees ha−1 that included intercropping for the first 6 years provided the greatest cumulative net margin after 20 years. The financial benefit of intercropping over the first 6 years opposed to monoculture walnut fruit production appeared to be consistent across the three tree densities studied. These results suggest that silvoarable agroforestry is profitable approach to establishing walnut orchards.

The incorporation of trees on traditional agricultural land has the potential for providing beneficial conditions for understory crops by altering the microclimate. Under these assumptions, we conducted a study on maize productivity intercropped in a 14-year-old walnut orchard by measuring growth and yield parameters, and water and nutrient uptake. Overall, we found that walnut trees decreased maximum air temperature and increased air humidity, especially during hot summer months characterized by precipitation deficit. A 30% reduction in maize yield per total area was a result of significantly reduced plant density, which could be a walnut-specific effect due to juglone excretion. Productivity per plant increased as shown by a significantly higher harvest index and 1000 kernel weight. No meaningful differences were found in terms of maize grain nutrient productivity, nutrient recovery, or nutrient use efficiency. On the systems level, we observed an advantage of the walnut-maize system compared to its respective monoculture systems—land and water equivalent ratios showed that for gaining the same yields as in intercropped system, walnut and maize grown separately would need 32% more land and 31% more water. Our study implies there are some beneficial outcomes to growing maize with trees, although further research should focus on investigating walnut as an option, due to its possible allelopathic effects.

Intercropping arable crops in orchards is a sustainable land use for intensifying agricultural production, under the condition of plants’ complementarity in sharing resources. This study investigated the aspects of water use and yields in intercropped systems of walnut and crops. To assess possible temporal complementarity between crops and trees, a summer crop—buckwheat—and a winter crop—barley—were intercropped in walnut orchards. The land and water productivity were studied under two designs: in an older, denser orchard and a younger one, with wider tree spacing. The results showed a reduction in yields and water productivity (WP) of intercrops due to the competition with walnut trees, with the exception of buckwheat in the younger orchard, where this summer crop surprisingly achieved the highest yield and WP. Nevertheless, in the system with mature fruiting trees, intercropping with winter barley was 53% more productive per unit of land and 83% more water-productive than growing walnut and barley separately but also 48% more land-productive and 70% more water-productive than the walnut–buckwheat system. Our results indicate positive effects of trees on microclimates but also emphasize the importance of species selection and systems design on the overall productivity of intercropped systems.

Intercropping arable crops between tree rows has proven to be a great alternative to conventional agriculture in terms of food production sustainability and climate change adaptation. However, close interactions between species in these systems sometimes yield adverse allelopathic effects. In this study, the possibility of intercropping barley and maize in the walnut orchard was investigated in terms of walnut leaf litter toxicity. Leaves from 15 and 30 years old walnut trees were used to prepare water extracts out of freshly fallen leaves and soil with leaves decomposed within. Barley and maize seeds were germinated in these extracts using between paper towels method. Fresh leaf litter extracts slightly reduced barley germination but significantly inhibited both barley and maize seedlings’ growth. The extract from older walnut tree leaves had the most severe toxic effect, and seedlings shoot was more sensitive than root for both species. A significant correlation was observed between extracts pH and seedlings lengths, suggesting the hydrogen-induced injury to the root, which consequently influenced growth. Decomposed leaf litter extract had a promotional effect on barley and maize germination and growth, which shows that appropriate walnut litter management could improve the performance of intercropped walnut systems.

Crimson clover (Trifolium incarnatum L. convar. Inkara) seeds were imbibed with water solution of various pH values (4, 5, 6 and 7) at various ambiental temperatures (10, 15 and 22 °C) with the aim to reveal treatments effects on seed (imbibition, germination energy, germination and electric conductivity) and seedling traits (stem, root and total length).Seeds were imbibed in a laboratory by the standard method for seed germination. When averaged over the inquired pH values, ambient temperature affected all the investigated traits except stem length. The highest seed imbibition (58.8%) and electric conductivity (82 µS/cm per gram) were achieved at 22 °C. The highest values for germination energy (70%), germination (68%), root length (31 mm) and total seedling length (77 mm) were achieved at 10 °C. When averaged over the inquired ambiental temperatures, the highest germination energy (71%), germination (73%), root length (34 mm) and total seedling length (78 mm) were achieved at pH 4.