Alfalfa stand age at termination influences soil properties, root characteristics, and subsequent maize yield

Abstract

Alfalfa (Medicago sativa L.)–maize (Zea mays L.) rotation is an important cropping practice to improve crop production and soil fertility, but the effects of the alfalfa stand age on the performances of the following maize remain unexplored. It is not clear how different alfalfa stand ages at termination influence soil properties, root characteristics, and yield of subsequent maize. The aim of this study was to evaluate how alfalfa influences soil characteristics, which in turn influence the root and aboveground growth and grain yield of the following maize crop. A field experiment from 2014 to 2019 was conducted at the Lishu Experimental Station, Jilin Province, China. The field treatments included six years of continuous maize (CM), six years of continuous alfalfa (CA), three years of alfalfa followed by two years of maize (3A2M), four years of alfalfa followed by two years of maize (4A2M), and five years of alfalfa followed by one year of maize (5A1M). Only the yield for the first-year maize after alfalfa in the 3A2M, 4A2M, and 5A1M treatments significantly increased by 8 %, 23 %, and 13 %, respectively. Root biomass (RB) of CA treatment gradually increased from 2014, reaching its maximum value of 5866 kg ha−1 in 2019, which was 35 % greater than the RB accumulation under CM in the 0–60 cm soil layer. Compared with the CM treatment, 3A2M and 4A2M treatments increased RB, while 3A2M, 4A2M, and 5A2M increased root length density (RLD), root surface area density (RSAD), and root volume density (RVD) of first-year maize after alfalfa. The 4A2M treatment also increased RLD, RSAD, and RVD in the 0–60 cm soil layer of second-year maize and reduced the soil bulk density (BD) in the 0–20 cm soil layer of first-year maize after alfalfa. Only 4A2M and 5A1M treatments significantly increased soil Olsen-P and soil organic carbon by first-year maize after alfalfa. The redundancy analysis results showed that the soil water content in the critical period and soil Olsen-P were the primary factors, which explained 33.8 % and 13.0 % of variation in maize root characteristics (P < 0.01), respectively. Structural equation modeling indicated that sowing alfalfa influenced the subsequent maize yield by influencing the soil Olsen-P, soil mineral nitrogen before sowing, and root characteristics. Therefore, keeping alfalfa for at least four years should be the recommended practice owing to its ability to improve the soil properties, root growth, and subsequent maize yield.