[Effects of the photovoltaic-earthworm model and organic material application on soil quality]

We investigated the effects of earthworm and organic material application methods on soil quality on slopes where photovoltaic panels are installed, aiming to explore a new model for promoting sustainable development of photovoltaic agriculture and improving soil quality. We proposed the photovoltaic-earthworm model, which involves breeding Amynthas aspergillum with high medicinal value in the soil under photovoltaic panels. There were four treatments: surface application of cow manure between photovoltaic panels to breed earthworms (Out+S), surface application of cow manure under photovoltaic panels to breed earthworms (In+S), mixed application of cow manure between photovoltaic panels to breed earthworms (Out+M), and mixed application of cow manure under photovoltaic panels to breed earthworms (In+M), with the bare land as the control (CK). We measured soil physical and chemical properties, as well as the enzyme activities. The results showed that the content of soil mechanical stability and water stability macroaggregates, organic carbon, total nitrogen, alkaline nitrogen, available phospho-rus, available potassium, and acid phosphatase activity, were significantly enhanced in Out+M and In+M treatments compared to CK by 4.7%-18.7%, 6.2%-26.0%, 37.5%-113.9%, 39.4%-90.9%, 43.4%-196.8%, 222.9%-762.5%, 246.1%-460.7% and 25.3%-33.3%, respectively. The content of soil mechanical stability and water stability macroaggregates under photovoltaic panels (In) was increased by 13.4%-21.5% and 16.1%-16.2%, respectively, compared to between photovoltaic panels (Out). The soil alkaline nitrogen content, carbon nitrogen ratio, and acid phosphatase activity was increased by 18.5%-34.1%, 13.8%-16.8%, and 6.3%-36.5%, respectively. The content of soil mechanically stable macroaggregates, water stable macroaggregates, and water stable macroaggregates with particle size ≥0.25 mm in mixed application of cow manure (M) treatments was increased by 6.6%-14.3%, 18.5%-18.6%, and 3.2%-3.8%, respectively, compared to the surface application of cow manure treatment (S). The content of organic carbon, total nitrogen, alkaline hydrolyzed nitrogen, available phosphorus, carbon nitrogen ratio, and acid phosphatase activity was increased by 55.5%-88.2%, 37.0%-60.5%, 54.4%-74.6%, 102.4%-117.8%, 13.4%-16.4%, and 30.7%-67.7%, respectively. The destruction rate of soil aggregates decreased by 39.0%-50.9%. Soil macroaggregates were significantly positively correlated with organic carbon, soil nutrients, and acid phosphatase. Soil quality of each treatment followed an order of In+M>Out+M>In+S>Out+S>CK. In summary, In+M has the great potential for promoting local economic development, protecting the ecological environment, and improving soil quality in the development of slope photovoltaic agriculture in southern China.