Long-term application of biomass and reduced use of chemicals alleviate soil compaction and improve soil quality

Abstract

The heavy traffic of agricultural equipment in citric orchards as a result of frequent application of pesticides and fungicides have led to soil compaction and a biological imbalance in these agricultural ecosystems, decreasing crop yields and increasing production costs. The purpose of this work was to assess the effects of spontaneous vegetation (weed) management in interrows following the replacement of agrochemicals with alternative inputs known to have a low impact on the environment. This experiment was conducted in a commercial orchard of ‘Murcott’ tangor (Citrus reticulata, Blanco×Citrus sinensis, Osbeck). Highly soluble sources of NPK were substituted with a mixture of 65% rice bran+35% castor bean meal (3.0%N), thermophosphate (17.5% P2O5) and potassium sulfate (48%K2O). Synthetic pesticides were replaced with alternative pest controls, such as Bordeaux mixture and lime sulfur. Mechanical mowing was used instead of herbicides, and the mowed weeds were spread under the citrus plants canopy for mulch. This treatment, referred to as alternative management (AM), was performed for three years and compared with a control area, referred to as conventional management (CM), in which conventional cultivation practices and pesticide applications were maintained. The soil compaction, the fruit yield and select biological parameters were used for our assessment. When compared to the CM treatment, AM provided a higher vegetation cover and species diversity (especially for grasses), reduced soil resistance to penetration, better root growth in the topsoil layer, increased root colonization by arbuscular mycorrhizal fungi (AMF), increased viable spores in the soil and a higher leaf boron (B) concentration. Furthermore, the infestation of the AM plots with the mealybug, Orthezia praelonga, was significantly lower, and the fruit yield was higher in the third year. These results indicate that agricultural management practices focused on a reduced impact on the agroecosystem, mainly with regard to biological processes, are promising techniques for sustainable agriculture.