Abstract
Tea is an economic shrubby plant in tropical and subtropical regions of the world. To obtain high yield in tea cultivation, chemical fertilizer application rates have generally been used. However, a large quantity of chemical fertilizer application in a long-term continuously ratooned and monoculture tea orchard can inevitably lead to soil acidification and a decline in fertility. Therefore, the restoration of soil fertility and the sustainable development of tea planting by organic ways are critical for the tea industry. In this study, field trials were conducted in the tea orchard that was continuously ratooned and mono-cultured for 20 years. Nitrogen fertilizer (NF), Laredo soybeans green manure (LF), and goat manure (GM) treatments were applied to restore optimum acidity, soil fertility, microbial activity, and the community structure of a long-term continuously monoculture tea orchard. This paper investigated that the pH value was increased from 4.23 to 4.32 in GM and LF, respectively. Similarly, the content of exchangeable acidity (EA) was decreased by 1.21 and 1.46 cmol·kg−1 in GM and LF, respectively. Available nutrient results indicated that the content of NH4+-N was increased by 3.96, 4.38, NO3−-N by 1.07, 2.16, AP by 3.46, 6.86, AK by 0.26, 0.3 mg kg−1 in GM and LF treatments, respectively. Enzyme analysis revealed that the activity of urease and sucrase was promoted by 7.98 mg·g−1·24 h−1 and 6.77 mg·g−1·24 h−1, respectively, in LF treatment. Likewise, the activity of acid phosphatase and polyphenol oxidase was sharply increased by 2.3 mg·g−1 h−1 and 63.07 mg·g−1 h−1 in LF treatments. Additionally, the activity of urease, sucrase, acidic phosphatase, polyphenol oxidase, and peroxidase were also significantly increased by applying GM treatments. Meanwhile, LF and GM treatments significantly improved soil microbial biomass as well as low weight organic acid content in degraded tea rhizosphere. Furthermore, high throughput sequence results illustrated that the relative abundance of Rhizobiaceae and Bradyrhizobiaceae families increased in LF and GM treatments, respectively, which are mostly a kind of nitrogen fixer and plant growth promoting bacteria. Taken together, the physiological traits of the new sprouts and the biochemical components of new tea leaves were also significantly improved by GM and LF treatments. From this study, it is concluded that LF and GM are good agriculture management practices, which promote plant growth, yield, and nutrient availability by maintaining and improving pH, enhancing available nutrients status, improving the secretion of low molecular weight organic acids, and balancing the microbial community structure in the long-term mono-cultured tea orchard.
Highlights
When applying different fertilizers for three consecutive years to monoculture a degraded tea orchard, the release of effective nutrients in tea rhizosphere was promoted by LF and Goat manure (GM) treatments as well as by Nitrogen fertilizer (NF) treatment
The exchangeable Ca2+ was increased by 1.91, 2.48 cmolc.kg−1 and exchangeable Mg2+ by 0.19, 0.11 cmolc.kg−1 in NF and GM treatments, respectively (Table 1). It means that legume forage-goat manure applications have the ability to maintain the fertility of tea rhizosphere soil as chemical fertilizers
In GM treatment, the sprouts length was improved by 42.06%, the content of the third leaf’s chlorophyll was increased by 4.42%, and the photosynthetic rate (Pn) of the leaf was increased by 5.96% (Figure 3a–c). These results showed that the tea ‐ Legume – goat model could effectively improve the physiological growth of tea shoots in the rhizosphere soil of the tea plant without applying nitrogen fertilizer in organic tea gardens
Summary
The application of nitrogen fertilizer is an effective mean for obtaining high yield in tea cultivation. Nitrogen fertilizer in the rhizosphere soil of tea plant significantly reduced soil pH, while extractable Al levels grew [2,3]. The pH of long-term tea plantation decreased due to protons released from ammonium fertilizers preferentially for the growth [4]. Under the tea plantation, acidification took place within a soil depth of 70 cm, with the maximum difference in pH in the upper 17 cm (∆pH = 2.80) [5]. Most of the inorganic fertilizers were fixed to free iron and aluminum oxide in the soil by weathering and leaching, which cause nutrient sequestration in long-term tea plantations [9,10]
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