Ecological and Agronomic Benefits of Intercropping Maize in a Walnut Orchard—A Case Study

Abstract

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.

The Influence of Trees on Crop Yields in Temperate Zone Alley Cropping Systems: A Review

“…The soil water content in ACS can also differ depending on the timing during the growing period and the developmental stage of crops. This was shown in a study from Croatia, where maize productivity was assessed in a 14-year-old walnut orchard [64]. It was found that the intercropped system conserved more water in late spring during the early stages of maize development but had much lower soil water content later in the growing period during the dry summer months.…”

“…The existence of spatial competition between trees and crops is well documented (Table A1, [34,41,47,48,58,60,66,67]). Similarly, lower soil moisture was often associated with lower crop yields, either in close vicinity to tree rows or in the whole ACS (Table A1, [29,33,39,41,44,56,64]).…”

“…There is consensus amongst researchers that the establishment of AFS and ACS has many beneficial effects on water cycling processes and hydrological ecosystem services (ES, [62]). These include the improvement of soil water storage, recharge and retention, enhanced water infiltration, improved water quality, reductions in the amount of nutrient leaching to the groundwater body, as well as the reduction of runoff and water erosion [13,63,64]. However, when it comes to the distribution of soil water reserves, the spatial proximity of trees and crops can also have adverse effects.…”

“…Higher soil moisture contents in ACS have been found next to black locust tree rows in the ACS on the reclamation site in Germany [32], in four to eight meter distances to poplar tree rows in the ACS with summer barley and rapeseed in Germany [33], at the beginning of the growing period in the orchard with walnut and maize in Croatia [64] and adjacent to an eight meter high hedgerow in Austria [71]. Here, soil moisture values and crop yields of lucerne were higher close to the hedgerow and decreased with increasing distance to it, which, according to the authors, signifies an interrelation between those two parameters.…”

“…Six studies included in this review addressed the impact of the tree species on crop productivity (Table A1, [29,42,44,57,60,64]). In an ACS in Indiana, USA, maize yields were lower next to black walnut tree rows compared to red oak tree rows [60].…”