Yield and economic benefit of corn/needle leaf pea intercropping system under different nitrogen fertilizer reduction rates

Objectives The potential of nitrogen (N) fertilizer reduction in the corn/needle leaf pea intercropping system was studied in the Hexi oasis irrigation area to provide a theoretical basis for the efficient use of N resources.

Methods The long-term field experiment of corn/needle leaf pea intercropping was located in the Wuwei oasis irrigation area since 2011. The experimental treatments were no fertilizer application (i.e., control) and conventional N fertilizer application (N100) under the mono-maize system, and corn/needle leaf pea intercropping system with the conventional N fertilizer was applied at 95%, 90%, 85%, 80% and 0% of the conventional rate. The maize and needle leaf pea yield, maize yield components, and the economic benefits of the intercropping system were investigated from 2014 to 2019. The partial productivity of N (PPN), agronomic efficiency of N (AEN), and the N fertilizer contribution rate (FCRN) were calculated.

Results The corn/needle leaf pea intercropping had obvious yield advantages, and the merit increased with the elongation of experimental years. Compared with N100, the intercropped corn grain yield under 85% N application rate did not change significantly (P > 0.05), although the plant height and stem diameter of corn was inhibited. Spike height to plant height rate decreased; spike number per area, grain number per spike and 100-grain weight had no obvious change. The harvested needle leaf pea hay and grain were 1419 kg/hm² and 1637 kg/hm², corresponding to an increased economic benefit of 3813 yuan/hm². The PPN and AEN (P < 0.05), and the FCRN (P < 0.05) decreased in 2019, but the decrease in other years were not significant. When the N application rate was 80% of the conventional rate, the intercropped corn grain yield (P < 0.05) decreased by 8.77%. However, the harvest of 1438 kg/hm² needle leaf pea hay and 1569 kg/hm² needle leaf pea grain in the intercropping system increased the economic benefit of the system by 2098 yuan/hm². The PPN significantly increased by 14.04%, and the AEN had no obvious change. However, spike number per area, grain number per spike, 100-grain weight, plant height, stem diameter, spike height, spike length, spike diameter, and the FCRN of corn significantly decreased.

Conclusions Under long-term corn/needle leaf pea intercropping, the highest N reducing potential is 15%, with no decrease in corn yield and the additional harvest of needle leaf pea hay and grain increases the economic benefits. The highest N reducing potential in corn is 20% under intercropping of corn and neddle leaf pea, in which the decreased corn yield and FCRN could be compensated by the harvest of needle leaf pea hay and grain, and the economic benefits of the intercropping system and PPN are significantly increased in the Hexi oasis irrigation area.