Effects of maize ǁ peanut intercropping and arbuscular mycorrhizal fungi inoculation on soil enzyme activity and their stoichiometry

In this study, a two-factor randomized block experimental design was used, and the factors were inoculation treatment and planting mode. Two inoculation treatments were set up, i.e., inoculation with arbuscular mycorrhizal fungi (AMF) and non-inoculation with AMF (NA). Three planting patterns were maize monoculture (SM), peanut monoculture (SP) and maize‖peanut intercropping ( intercropping maize was IM, intercropping peanut was IP ).

The two factors had a total of 6 experimental treatments, each treatment had 5 replicates, a total of 30 plots. The specifications of the residential area are unified as 12 m long and 4 m wide, and the area of the residential area is 48 m2. The plant spacing of maize in single and intercropping plots was 3 plants·m-1, and the plant spacing of peanut was 15 plants·m-1 ( two plants in one hole ).

The row spacing of maize and peanut was 0.5 m, and the intercropping row ratio was 4 : 4. All treatments were applied with the same amount of base fertilizer, 100 kg·hm-2 compound fertilizer (N-P₂O₅-K₂O content of 15%-15%-15% ), one-time strip application before sowing, no topdressing at the growth stage of peanut, and 50 kg N·hm-2 nitrogen fertilizer ( urea, containing 46.0 % N ) at the jointing stage of maize.

Before sowing, the arbuscular mycorrhizal fungi ( AMF ) were uniformly stirred after the surface of maize and peanut seeds was slightly tided with water, so that AMF was evenly attached to the seed surface, and the seed dressing amount was 750  g·hm-2. The tested peanut variety was “ Baisha 1016 ”, and the tested maize variety was “ Jingke 968 ”.AMF was purchased from Beijing Jinbilai Biotechnology Co., Ltd.Among them, 1g microbial agent contained about 110 AMF propagules.

It is sown around May 10 and harvested around September 25 every year. Soil samples were collected at the mature stage of the crop ( late September ). The corn and peanut plants were uprooted and gently shaken off the soil around the roots.

After fully mixed, they were placed in a self-sealing bag and stored in a dry ice refrigerator and brought back to the laboratory as soon as possible. After removing the plant residues and other magazines in the soil samples, the 2mm nylon sieve was passed and mixed evenly. Some samples were stored in a refrigerator at 4 °C as fresh soil for the determination of soil enzyme activity.

A part of the soil samples were dried in a cool place at room temperature and stored in a self-sealing bag to determine the basic chemical properties of the soil. The contents of total carbon and total nitrogen in soil were determined by elemental analyzer ( Elementar III, Germany ). The content of total phosphorus was determined by Lurukun 's method.

The content of total phosphorus was determined by NaOH melting-molybdenum antimony anti-colorimetric method. The soil pH ( water-soil ratio 2.5 : 1 ) was determined by pH meter ( 320-S, Mettler Toledo ). Five extracellular enzymes related to soil C, N and P cycles were selected for determination.

Among them, soil β-1,4-glucosidase, soil β-cellobiohydrolase and soil β-1,4-N-acetylglucos-aminidase were all determined by p-nitrophenol method. Soil leucine aminopeptidase was determined by leucine p-nitroaniline method. Soil acid phosphatase was determined by disodium phenyl phosphate method.

All enzyme activity units were expressed as nmol·g-1·h-1.Extracellular enzymes related to soil C cycle : soil β-1,4-glucosidase, abbreviated as BG ; soil β-cellobiohydrolase,abbreviated as CBH.Soil N cycle-related extracellular enzymes:soil β-1,4-N-acetylglucos-aminidase, abbreviated as NAG ; soil leucine aminopeptidase, abbreviated as LAP. Soil N cycle related extracellular enzyme : soil acid phosphatase, abbreviated as PHOS.

Microsoft Excel 2010 was used to collate the data, OriginPro 2024 was used for mapping, and SPSS Statistics 23 was used for two-way ANOVA analysis of intercropping and mycorrhizal fungi inoculation to clarify the individual and interaction effects of intercropping and mycorrhizal fungi inoculation. Redundancy analysis ( RDA ) was performed using Canoco5 to determine the effect of soil physical and chemical properties on enzyme stoichiometry.