Bi-directional nitrogen transfer in an intercropping system of peanut with rice cultivated in aerobic soil

Three separate greenhouse experiments were conducted to determine the bi-directional N transfer in a peanut and rice intercropping system using the direct 15N foliar feeding technique at N application rates of 15, 75 and 150 kg ha−1. When peanut was used as the 15N donor plant, the atom % 15N in the rice shoot was consistently higher than in control rice, indicating that 15N transfer from peanut to the associated rice crop occurred. The percentage of N transfer (%NT) from peanut to the associated rice was 9.9%, 5.7% and 4.2% at the three N application rates, respectively. The N transferred from peanut to rice was 22.6, 15.5 and 8.2 mg N plant−1, accounting for 10.9%, 6.4% and 3.1% of the total N accumulated in rice plants at the three N application rates, respectively. When rice functioned as the 15N donor plant, the %NTs were 4.4%, 2.1% and 1.4% and represented about 5.2%, 3.4% and 2.4% of total N accumulated in peanut shoot at the three N application rates, respectively. The net directional N transfer was from peanut to rice and this was calculated by the difference in the bi-directional transfers and was mainly due to peanut root decomposition. Thus, the %NTs were 10.7%, 6.3%, 5.1% and 3.5% on 28 July (the day on which peanut shoots were cut), 8 August, 28 August and 8 September, respectively, and correspondingly, the N transferred from peanut to rice represented 6.0%, 5.8%, 5.1% and 3.2% of the total N accumulated in the rice plants.