Assessing the impact of biochar and nitrogen application on yield, water-nitrogen use efficiency and quality of intercropped maize and soybean

Abstract

Introduction: Biochar (BC) and nitrogen (N) application have the potential to increase grain yield and resource use efficiency in intercropping systems. However, the effects of different levels of BC and N application in these systems remain unclear. To address this gap, the study is intended to ascertain the impact of various combinations of BC and N fertilizer on the performance of maize-soybean intercropping and determine the optimum application of BC and N for maximizing the effect of the intercropping system.

Methods: A two-year (2021-2022) field experiment was conducted in Northeast China to assess the impact of BC (0, 15, and 30 t ha^-1) and N application (135, 180, and 225 kg ha^-1) on plant growth, yield, water use efficiency (WUE), N recovery efficiency (NRE) and quality in an intercropping system. Maize and soybean were selected as materials in the experiment, where every 2 rows of maize were intercropped with 2 rows of soybean.

Results and discussion: The results showed that the combination of BC and N significantly affected the yield, WUE, NRE and quality of intercropped maize and soybean. The treatment of 15 t ha^-1 BC and 180 kg ha^-1 N increased grain yield and WUE, while that of 15 t ha^-1 BC and 135 kg ha^-1 N enhanced NRE in both years. Nitrogen promoted the protein and oil content of intercropped maize, but decreased the protein and oil content of intercropped soybean. BC did not enhance the protein and oil content of intercropped maize, especially in the first year, but increased maize starch content. BC was found to have no positive impact on soybean protein, but it unexpectedly increased soybean oil content. The TOPSIS method revealed that the comprehensive assessment value first increased and then declined with increasing BC and N application. BC improved the performance of maize-soybean intercropping system in terms of yield, WUE, NRE, and quality while N fertilizer input was reduced. The highest grain yield in two years was achieved for BC of 17.1-23.0 t ha^-1 and N of 156-213 kg ha^-1 in 2021, and 12.0-18.8 t ha^-1 BC and 161-202 kg ha^-1 N in 2022. These findings provide a comprehensive understanding of the growth of maize-soybean intercropping system and its potential to enhance the production in northeast China.

Keywords: NRE; NUE; biochar; maize-soybean intercropping; nitrogen application; yield.

Figure 1

Rainfall and daily average temperature during the period of test. (A) stands for rainfall and daily average temperature during the period of test in 2021, (B) stands for rainfall and daily average temperature during the period of test in 2022.

Figure 2

Schematic diagram of maize-soybean intercropping. BC application rates: 0 t ha^-1 (C₀), 15 t ha^-1 (C₁) and 30 t ha^-1 (C₂); N application rates: 135 kg ha^-1 (N₁), 180 kg ha^-1 (N₂), 225 kg ha^-1 (N₃). BC was mixed uniformly into the soil at a depth of 30 cm before sowing in 2021 but was not applied in the following year. N fertilizer was applied before sowing in the two years.

Figure 3

Maize-soybean intercropping system comprehensive evaluation hierarchical model.

Figure 4

Yield of maize-soybean intercropping system in 2021 and 2022. (A) shows the yield in 2021 and (B) shows the yield in 2022. Different lowercase letters indicate significant differences among different treatments (P<0.05). The column bars and error bars represent the mean yield of three replicates and the standard deviation of the mean, respectively. BC application rates: 0 t ha^-1 (C₀), 15 t ha^-1 (C₁) and 30 t ha^-1 (C₂); N application rates: 135 kg ha^-1 (N₁), 180 kg ha^-1 (N₂), 225 kg ha^-1 (N₃). BC was mixed uniformly into the soil at a depth of 30 cm before sowing in 2021 but was not applied in the following year. N fertilizer was applied before sowing in the two years.

Figure 5

Maize quality in 2021 and 2022. (A, B) show maize protein content in 2021 and 2022, respectively. (C, D) show maize oil content in 2021 and 2022 respectively, and (E, F) show maize starch content in 2021 and 2022 respectively. Different lowercase letters in the same column mean significant differences among different treatments at 0.05 level. The column bars and error bars represent the mean maize quality of three replicates and the standard deviation of the mean, respectively. BC application rates: 0 t ha^-1 (C₀), 15 t ha^-1 (C₁) and 30 t ha^-1 (C₂); N application rates: 135 kg ha^-1 (N₁), 180 kg ha^-1 (N₂), 225 kg ha^-1 (N₃). BC was mixed uniformly into the soil at a depth of 30 cm before sowing in 2021 but was not applied in the following year. N fertilizer was applied before sowing in the two years.

Figure 6

Soybean quality in 2021 and 2022. (A, B) show soybean protein content in 2021 and 2022, respectively. (C, D) show soybean oil content in 2021 and 2022, respectively. Different lowercase letters in the same column mean significant differences among different treatments at 0.05 level. The column bars and error bars represent the mean soybean quality of three replicates and the standard deviation of the mean, respectively. BC application rates: 0 t ha^-1 (C₀), 15 t ha^-1 (C₁) and 30 t ha^-1 (C₂); N application rates: 135 kg ha^-1 (N₁), 180 kg ha^-1 (N₂), 225 kg ha^-1 (N₃). BC was mixed uniformly into the soil at a depth of 30 cm before sowing in 2021 but was not applied in the following year. N fertilizer was applied before sowing in the two years.

Figure 7

Effects of BC or N application on comprehensive evaluation score of maize-soybean intercropping system. y_C1 and y_N1 is the function of the single-factor effect function of on the comprehensive evaluation score in 2021, and y_C2 and y_N2 is single-factor effect function of comprehensive evaluation score in for 2022.

Figure 8

Coupling effect of BC and N on comprehensive evaluation score of Maize-Soybean intercropping system in 2021 and 2022.