Agroforestry has been widely practiced in the Loess Plateau region of China because of its prominent effects in reducing soil and water losses, improving land-use efficiency and increasing economic returns. However, the agroforestry practices may lead to competition between crops and trees for underground soil moisture and nutrients, and the trees on the canopy layer may also lead to shortage of light for crops. In order to minimize interspecific competition and maximize the benefits of tree-based intercropping systems, we studied photosynthesis, growth and yield of soybean (Glycine max L. Merr.) and peanut (Arachis hypogaea L.) by measuring photosynthetically active radiation, net photosynthetic rate, soil moisture and soil nutrients in a plantation of apple (Malus pumila M.) at a spacing of 4 m × 5 m on the Loess Plateau of China. The results showed that for both intercropping systems in the study region, soil moisture was the primary factor affecting the crop yields followed by light. Deficiency of the soil nutrients also had a significant impact on crop yields. Compared with soybean, peanut was more suitable for intercropping with apple trees to obtain economic benefits in the region. We concluded that apple-soybean and apple-peanut intercropping systems can be practical and beneficial in the region. However, the distance between crops and tree rows should be adjusted to minimize interspecies competition. Agronomic measures such as regular canopy pruning, root barriers, additional irrigation and fertilization also should be applied in the intercropping systems.
1. Complementarity (CE) and selection effects (SE) have been either invoked to explain the positive diversity-productivity relationship in natural and semi-natural ecosystems. Few studies have, however, separated selection and complementarity effects in economically valuable intercropping systems, which receive significant nutrient inputs throughout the growing season.2. We performed a 2-year field experiment with five cropping systems (i.e. maize/ peanut intercropping, maize/soybean intercropping, maize, peanut and soybean monocultures) under different combinations of nitrogen (N) and phosphorus (P) fertilization. Sequential harvest of subplots was performed five times during the growing season and the additive partitioning method was applied to determine complementarity and selection effects in the two intercropping systems.3. We found that the land equivalent ratio (LER) based on yield was greater than or close to 1 in both maize/soybean and maize/peanut intercropping systems, suggesting yield advantages in these intercropping systems compared to monocultures. The LER of the two intercropping systems without N fertilization was greater in 2018 than in 2017. Nitrogen fertilization reduced the LER of maize/ soybean intercropping in 2018, and that of maize/peanut intercropping across 2 years. Nitrogen fertilization had much stronger effects on maize yield than on soybean or peanut yield. Intercropping increased maize yield but decreased soybean and peanut yield.4. The CE was more important for net biodiversity effects without N fertilization while the SE was more important with N fertilization in the two intercropping systems across 2 years. Phosphorus fertilization impacts on the LER and biodiversity effects were weaker compared to N fertilization. Finally, net biodiversity effects were greater at later growth stages within a growing season. Synthesis and applications.Our study demonstrates how yield advantages of species-diverse intercropping systems can be maximized either through (a) CE in the absence of N fertilization thanks to complementarity in nutrient use between crops or (b) SE under N fertilization thanks to overyielding of highly productive species (i.e. maize). Yield advantages promoted by CE are more sustainable because they are associated with reduced chemical fertilizer use and greater monetary
In arid and semi-arid areas, interspecific below-ground competition is prominent in agroforestry systems. To provide theoretical and technical guidance for the scientific management of apple–crop intercropping systems, a field study was conducted in the Loess Plateau of China to examine the variation of fine roots distribution in apple–crop intercropping systems. The fine roots of apple trees and crops (soybean (Glycine max (L.) Merr) or peanuts (Arachis hypogaea Linn.)) were sampled to 100 cm depth at ten distances from the tree row using the stratified excavation method. The results showed that the vertical distribution of fine roots between intercropped apple trees and intercropped crops were skewed and overlapped. Apple–crop intercropping inhibited the fine roots of apple trees in the 0–60 cm soil depth, but promoted their growth in the 60–100 cm soil depth. However, apple–crop intercropping inhibited the fine roots of intercropped crops in the 0–100 cm soil depth. For the fine roots of each component of the apple–crop intercropping systems, variation in the vertical distribution was much greater than variation in the horizontal distribution. Compared with monocropped systems, apple–crop intercropping caused the fine roots of intercropped apple trees to move to deeper soil, and those of intercropped crops to move to shallower soil. Additionally, apple–crop intercropping slightly inhibited the horizontal extension of the fine-root horizontal barycentre (FRHB) of intercropped apple trees and caused the FRHB of intercropped crops to be slightly biased towards the north of the apple tree row. Variation of the fine roots distribution of each component of the apple–soybean intercropping system was greater than that of the apple–peanut intercropping system. Thus, the interspecific below-ground competition of the apple–peanut intercropping system was weaker than that of the apple–soybean intercropping system. Intense competition occurred in the apple–peanut intercropping system and the apple–soybean intercropping system was in sections whose distance ranged from 0.5–1.3 and 0.5–1.7 m from the tree row, respectively. The interspecific below-ground competition was fiercer on the south side of the apple tree row than on the north side.
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