Using APSIM to optimize corn nitrogen fertilizer application levels in alfalfa-corn rotation system in Northeast China.

Alfalfa (Medicago sativa L.) consumes a large amount of soil inorganic nitrogen (N) but can supply ample rhizosphere deposited N to subsequent crops. Therefore, N fertilizer application levels should be optimized for corn under long-term alfalfa-corn (AC) rotation system to achieve high yield and N use efficiency. The present study assessed the yield and water and N use efficiency of corn under N fertilizer application in a long-term AC cropping system and optimized the corn N fertilizer application level using the Agricultural Production Systems sIMulator (APSIM). APSIM was calibrated and validated utilizing the experimental datasets of yield, aboveground biomass, plant N uptake, soil water storage, and inorganic N at 0−140 cm soil layer during corn growth with four N fertilizer treatments (0, 130, 195, and 260 kg N ha−1), which were collected from a six-year-old alfalfa field experiment carried out in Lishu County (Jilin Province, China) from 2020 to 2022; the field experiment was initiated in 2014. The validated APSIM was then utilized to simulate the long-term (1981−2020) characteristics of crop and soil under different corn N fertilizer application levels in a continuous corn (CC) cropping system and different alfalfa-corn rotation systems (one, two, three, four, and five years of alfalfa followed by two years of corn; 1A2C, 2A2C, 3A2C, 4A2C, 5A2C). The simulated N treatments included 0−300 kg N ha−1 range with an increment of 30 kg N ha−1. Model evaluation revealed that APSIM effectively captured the dynamics of the crop, soil water, and soil inorganic N during corn cultivation following alfalfa at four N fertilizer application levels. The normalized root-mean-square errors between the observed and simulated values under different treatments were less than 30 %. Alfalfa had legacy effects on the soil water and soil N mineralization (N min) of subsequent first-year corn, which ensured the corn yield following alfalfa. The first-year net N min in the soil with corn following alfalfa increased by 140 % (65 %−268 %) compared to the CC cropping system. Alfalfa planting also increased the 0−140 cm soil inorganic N before sowing (N sow) by 351 % (292 %−463 %) for the subsequent corn with no N fertilizer application and the 0−140 cm soil water storage before sowing by 22 % for the subsequent corn with relatively high N fertilizer application (300 kg N ha−1) compared to the CC cropping system. The highest yield and N use efficiency could be achieved by applying 90 kg N ha−1 N fertilizer for 1A2C/2A2C/3A2C rotation systems and 60 kg N ha−1 N fertilizer for 4A2C/5A2C rotation systems to the first-year corn following alfalfa. However, the N fertilizer requirement of the second-year corn following alfalfa under AC rotation systems was the same as that under the CC cropping system (150 kg N ha−1). The present study's findings indicate 60 kg N ha−1 N fertilizer application to the first-year corn following alfalfa under 1A2C/2A2C/3A2C rotation systems and 90 kg N ha−1 under 4A2C/5A2C rotation systems. The study provides a deeper understanding of alfalfa's effects on subsequent corn and a guidance for planning N fertilizer management in corn production following alfalfa. • 1st-yr corn following 1–3- and 4–5-year-old alfalfa required 60 and 90 kg ha−1 nitrogen (N) fertilizer, respectively. • Net N mineralization in the first-year corn following alfalfa improved by 140 % compared to continuous corn (CC). • Initial inorganic N (0−140 cm) in corn with no N fertilization following alfalfa was 351 % higher than that in CC. [ABSTRACT FROM AUTHOR]