Abstract
Alley cropping agroforestry systems (ACS) are ascribed to have manifold positive ecological effects; nevertheless their application is still limited due to uncertain productivity of the agricultural crop, especially in the tree-crop competition zone. Therefore, this study investigated the variability of oilseed rape and winter wheat yield, respectively, at different distances from the tree strip edge in 2016 and 2017 in an ACS established in 2008 in northern Germany. The ACS consisted of strips of fast-growing poplars alternating with narrow (48 m) and wide (96 m) crop alleys, each with a crop rotation including winter oilseed rape and winter wheat. Each tree strip contained 6 rows of poplars with a density of 10,000 trees per ha. Moreover, multi-year (2009–2016) crop yield data of oilseed rape and winter wheat in the narrow and wide crop alleys were compared with those of a corresponding non-agroforestry control field. In general, crop yields observed in 2016 and 2017 in the narrow crop alleys at 1 m from the tree strip edges were on average 77% (oilseed rape) and 55% (winter wheat) lower than in the middle of the crop alley. One reason for low yield close to the tree strips might be the leaf litter coverage of the seedlings in autumn. Leaf litter deposition was highest at 1 m on the windward and the leeward side of the tree strips in 2015 and on the leeward side in 2016, respectively. However, the average long-term crop yields of the narrow crop alley, the wide crop alley and the control field did not differ substantially among each other. Although oilseed rape and winter wheat yields were lower close to the tree strips, this yield reduction did not negatively influence the average long-term crop yields of the ACS.
Highlights
After decades of input-intensive agriculture, landscape clearing and monoculture farming in many developed countries, there is growing awareness that a transition of agricultural systems towards permanent preservation of natural resources as basis for future food security is imperative (FAO 2014)
The strong negative correlation between crop yield and leaf litter deposition in previous autumn indicates that leaf litter coverage can be a reason for the observed crop yield reduction near the tree strips
We found extremely low oilseed rape yield at 1 m on the windward side of the tree strip edge in 2016, leaf litter deposition in previous autumn at 1 m windward from the tree strip edge was only slightly higher than at the leeward side
Summary
After decades of input-intensive agriculture, landscape clearing and monoculture farming in many developed countries, there is growing awareness that a transition of agricultural systems towards permanent preservation of natural resources as basis for future food security is imperative (FAO 2014). To reach this goal, crop production should be performed in a ‘‘safe space’’, where food demands are met while agriculture-induced impacts on the environment are minimized (Bommarco et al 2013). Trees planted on agricultural land might contribute to reduced nutrient losses by rooting below the crop root zone and thereby increase seepage quality (Van Noordwijk et al 2006)
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