Abstract
Intercropping is an ancient agricultural practice that provides a possible pathway for sustainable increases in crop yields. Here, we determine how competition with wheat affects nutrient uptake (nitrogen and phosphorus) and leaf traits, such as photosynthetic rate, in maize. In a field experiment, maize was planted as a sole crop, in three different intercrop configurations with wheat (a replacement intercrop and two add-row intercrops), and as a skip-row system with one out of each three maize rows omitted. Nitrogen and phosphorus uptake were determined at flowering and maturity. Specific leaf area, leaf nitrogen concentration, chlorophyll content and photosynthetic rate of the ear leaf were determined at flowering. Nitrogen and phosphorus concentrations were significantly lower in intercropped maize than in sole maize and skip-row maize at flowering, but these differences were smaller at maturity. At flowering, specific leaf area was significantly greater in intercrops than in skip-row maize. Leaf nitrogen concentration was significantly lower in add-row intercrops than in sole maize, skip-row maize or maize in the replacement intercrop. Leaf chlorophyll content was highest in sole and skip-row maize, intermediate in maize in the replacement intercrop and lowest in maize grown in add-row intercrops. On the contrary, photosynthetic rate was significantly higher in the replacement intercrop than in sole maize, skip-row maize and the intercrop with an additional maize row. The findings indicate that competition with intercropped wheat severely constrained nutrient uptake in maize, while photosynthetic rate of the ear leaf was not negatively affected. Possible mechanisms for higher photosynthesis rate at lower leaf nitrogen content in intercropped maize are discussed.
Highlights
Intercropping is the cultivation of two or more crop species simultaneously in the same field (Vandermeer 1989)
There were no significant differences between the replacement intercrop and the add-row intercrops
The aim of this paper was to test four hypotheses: (i) maize has lower nitrogen and phosphorus uptake when grown in intercrops than in sole and skip-row maize; (ii) maize has a lower nitrogen content and chlorophyll content when grown in intercrops than as sole or skiprow maize; (iii) maize has a higher specific leaf area (SLA) when grown in intercrops than in sole and skip-row maize due to shade avoidance; (iv) maize has a lower photosynthetic rate when grown in intercrops than sole and skip-row maize due to a lower nitrogen content and a higher SLA
Summary
Intercropping is the cultivation of two or more crop species simultaneously in the same field (Vandermeer 1989). Due to complementary resource use in time and space among different species, intercropped plants usually achieve—on average across species—a greater yield per plant than plants of the same species in sole crops. When intercropped species have similar growing periods, the intercropping advantage is usually based on species differences in resource acquisition strategy or a decrease of crop failure probability, especially under low input conditions. The yield advantage decreases with an increase in inputs when the growing period of the intercropped species is the same (Yu et al 2015). When intercropped species have different growing periods, e.g. in relay intercropping, the intercrop advantage is in part due to complementary resource use in time. Relay intercrops attain high LER especially at high input levels (Yu et al 2015)
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