Copper fertilization in soybean-wheat intercropping under no-till management

The increase of soil organic matter (SOM) content under no-till (NT) management of field crops can reduce the availability of copper (Cu) in the soil. A field experiment was conducted during two growing seasons (2014-2015 and 2015-2016) with the objective of determining optimum Cu rates and critical Cu levels in soybean-wheat intercropping in a NT management. We used a randomized block design consisting of five Cu rates (0, 1, 2, 4, and 8 kg ha(-1)) applied before the first soybean crop. Both soybean and wheat showed a significant yield response to Cu, and the estimated value for maximum yield (EVMY) was 4.4 and 4.2 kg ha(-1) Cu application for soybean and wheat, respectively. Wheat required available Cu levels of 15.5 (DTPA-TEA extractant) and 20.5 mg kg(-1) (Mehlich 1 extractant) in the soil for maximum yield, whereas for soybean maximum yields were obtained with 7.7 and 14.1 mg kg(-1), respectively, for the two extractants. For soybean, number of pods per plant (NPP) and Fe concentration in the grain were influenced by Cu rate, whereas in wheat Cu rate only affected plant height. Cu rates also had a positive effect on photosynthetic rate (A), intercellular CO2 level, transpiration rate, stomatal conductance, and chlorophyll content of soybean, and A and chlorophyll content in wheat. The results suggest the need to increase the amount of Cu applied to the soil in soybean-wheat intercropping in a NT management.