A new strategy to study pond soil chemistry in intensive and extensive cultures of Litopenaeus vannamei: A case study in Brazil

Abstract Improvements in the sampling of pond soil and bioremediation techniques can increase the efficiency of soil treatments by emphasizing zones of greater nutrient deposition. This work evaluated the relative deposition of nutrients and their statistical correlation in pond soils in intensive and extensive Litopenaeus vannamei farming. Soil samples were collected (n: 150) in six ponds at two marine shrimp farms (one intensive and one extensive) after being drained and harvesting the shrimp. The ponds were divided into 5 zones - Water Inlet (WI), Water Outlet (WO), Plateau (P), Ditch (D) and Feeder (F), of which five samples were collected in each zone. Soil texture, Total Carbon (TC), Total Organic Carbon (TOC), Total Nitrogen (TN), C/N ratio, Total Phosphorus (TP), Available Phosphorus (AP), aluminum (Al), calcium (Ca), magnesium (Mg), potassium (K) and pH (H2O) were analyzed. All variables were submitted to the Kolmogorov-Smirnov and Levene test to verify normality and homoscedasticity, respectively. Variables that met the requirements were compared by one-way ANOVA analysis of variance, and Tukey test or Student's t-test. The correlation of nutrient concentration was performed using linear regression. Soil from intensive and extensive cultivation ponds were classified as sandy loam and sandy, respectively. The deficiency of carbon and potassium, and excess of phosphorus in the pond soil of both farms was verified. The soil from the ponds of the intensive cultivation farm showed high relative deposition for TC, TOC, TN and AP near the Feeder (F) and the Water Outlet (WO), which infers that these zones (16.32% of the total pond area) may need higher treatment frequencies or different treatment from the other zones studied (WI, P and D). In the soil of the extensive cultivation ponds, the highest values for TC, TOC, TN and AP were found in the Water Inlet (WI), Ditches (D) and Feeder (F) (2.68% of the total pond area). This also indicates the need for higher treatment frequencies or different treatment from the other zones studied (WO and P). In addition, results suggest that phosphorus is the nutrient with the greatest potential for accumulation in the soil, either organically or inorganically, due to its high adsorption potential, occurring mainly in areas of organic matter decomposition regardless of the cultivation system, while nitrogen was mainly organic due to its low adsorption potential. Therefore, based on this study it is recommended that as part of their soil management strategy, shrimp farmers treat the pond areas in a differentiated manner giving special attention to areas of organic matter decomposition with the goal of avoiding waste and increasing production efficiency, potentially saving up to 97% in probiotic products.