The objective of this study is to simulate green manure management in the actual production of grassy peach orchards, investigate the release law of medium and trace elements (MTE) after green manure was continuously incorporated into the soil, and to examine the effects of continuous grass on soil available nutrients in peach orchards, so as to provide reasonable grass planting and scientific formulation of nutrient management measures in peach orchard.

The grass-planting experiment was carried out in a peach orchard where grass was sown in 2016. Two treatments were set up: inter-row planting of ryegrass (RG) and hairy vetch (HV), and the mulching of black ground fabric (BF) was used as the control. In 2021 and 2022, soil available MTE content was measured at four key stages: pre-surface return (before mowing) and pre-burial (before incorporation) of green manure. The nutrient release characteristics of green manure were conducted using the nylon net bag method. The first stubble green manure was subjected to 100 d of surface decomposition followed by 350 d of burying decomposition, and the second stubble green manure was subjected to 100 d of surface decomposition. Element release patterns and residual quantities per unit area of green manure residues were analyzed over two consecutive years.

There was no significant difference in the initial content of Fe between the two types of green manure, while the initial content of Ca, Mg, and Cu in hairy vetch was significantly higher than in ryegrass. The accumulated release ratios of Ca, Mg, Mn, Cu, and Zn in ryegrass ranged from 2.65% to 55.43% during the surface decomposition of the first crop of green manure, all of which were significantly higher than those in hairy vetch. After the burying back to the field, the accumulated release ratios of Mn, Cu, and Zn in the residue increased overall. By the end of the test, the accumulated release ratios of Mn and Zn in hairy vetch reached 82.59% and 90.02%, respectively, which were significantly higher than those in ryegrass. Both species exhibited persistent Fe accumulation, with accumulated release ratios reaching -360.78% (RG) and -371.63% (HV) after 450 d. During the surface decomposition of the second crop green manure, Ca, Mg, and Zn were enriched in hairy vetch only, while Fe, Mn, and Cu were enriched in both of green manures. The differences in the release levels of various elements resulted in the residual amounts of Ca and Mg per unit area of green manure, which reached their highest values after 350 d of returning the first crop of green manure. However, the residual amounts of Fe, Mn, and Cu continued to increase at the end of the test. After continuous grass returning, the increase range of soil exchangeable Ca content in hairy vetch and ryegrass plots exceeded 13.13% and 23.56%, respectively, and the exchangeable Mg content increased by more than 13.85% and 20.51%, respectively. Compared with BF, by the end of the experiment, the available Mn content in the soil of HV increased by 63.16%, and the available Zn content in RG increased by 134.16%. However, the available Cu content of the HV and RG decreased by 37.90% and 36.06%, respectively, and the available Fe content was only 46.87% and 34.61% of the BF, respectively.

In the long run, perennial green manure application enhances soil exchangeable Ca and Mg, but reduces available Fe and Cu in peach orchards. In the short term, MTE fixed by green manure fails to completely release after 450 d of returning, and the enrichment time of Fe is the longest. In the early stage of grass planting in peach orchards, it is advisable to choose the mixed coverage mode of covering ground fabric in rows or under tree trays and planting green manure between rows. During the growth period of green manure, supplemental MTEs fertilization should be applied to effectively mitigate nutrient competition between peach trees and green manure and to promote the improvement of soil fertility in peach orchards.

Weed control is an important step for fruit tree production. To investigate the safety of different herbicides, suitable herbicides for peach nurseries and orchards were screened in peach production, which can provide theoretical basis for the application of chemical herbicides in the peach industry.

To preliminarily screen the safety of 13 herbicides, the peach seedlings combined with Lolium perenne, Cynodon dactylon, Alternanthera philoxeroides, Trifolium repens and Medicago falcata were evaluated in pot. Based on the results of the phytotoxicity index of each herbicide, 10% quizalofop-p-ethyl and 60% quinclorac were mixed. According to the effective doses of 25, 50, and 75 mL·hm^-2 of quizalofop-p-ethyl and 150, 300, 450 g·hm^-2 of quinclorac, a total of 9 herbicide mixtures were established. After 7, 14, and 21 d of stem and leaf spraying treatment, the weed inhibition rate was investigated. After 30 d of the treatment, the plant height, stem diameter, aboveground and underground biomass, electrolyte permeability of the leaf and root tip cells, total root length, total root surface area, root volume and root tip number of peach seedlings were also measured. Based on principal component analysis, the safety of different treatments was comprehensively evaluated.

After spraying on the stems and leaves of peach seedlings, 11 herbicides caused phytotoxicity in peach seedlings, resulting in varying degrees of symptoms such as chlorosis, wilting, and withering. However, quizalofop-p-ethyl and quinclorac had no significant effect on the growth of peach seedlings. After spraying weeds with a single agent of quizalofop-p-ethyl for 21 d, the inhibition rate of quizalofop-p-ethyl on gramineous weeds was 100%. However, it had no effect on broad-leaved weeds. On the contrary, the inhibition rate of spraying quinclorac on gramineous weeds was 0, and the inhibition rate range of M. falcata, T. repens and A. philoxeroides was 80% to 100%. After being mixed with quizalofop-p-ethyl and quinclorac, the total weed inhibition rate under 9 compound preparations could reach over 90% after 21 d. Meanwhile, each formulation had no significant effect on the height of peach seedlings, aboveground and underground biomass, electrolyte permeability of the leaf and root tip cells. The comprehensive analysis showed that the effective dose of quizalofop-p-ethyl had a significant impact on the comprehensive evaluation D value of the mixed formulation. When the effective dose of quizalofop-p-ethyl increased to 75 mL·hm^-2, the comprehensive evaluation D value of the mixed formulation exceeded 0.563, but there was no trend between the increasing D value and the increase of the effective dose of quinclorac.

Peach seedlings are sensitive to most herbicides, and mixing is an effective measure to improve the comprehensive weed inhibition rate of quizalofop-p-ethyl and quinclorac. After mixing an effective dose of 75 mL·hm^-2 quizalofop-p-ethyl with 300 g·hm^-2 quinclorac, the comprehensive evaluation D value of the formulation is the highest, which can achieve the best weed inhibition rate while ensuring the safety of peach seedlings.