Soil Mn spatial distribution and relationship between its availability and soil pH in a Kuerlexiangli pear orchard

Abstract:【Objective】The absorption of nutrient elements by plants depends not only on the absorption capacity of plant roots, but also on the availability of nutrient elements in the soil. Manganese plays an important role in the growth and development of fruit trees. In order to establish soil nutrient manage- ment system for production of Kuerlexiangli pear with high quality and yield, relationship between spatial distribution and availability of soil Mn and soil pH in a Kuerlexiangli pear orchard was studied.【Methods】The experiment was located in Korla City, central Xinjiang Uygur Autonomous Region (41°48′21′′N, 86°04′22′′E, with a total area of 7 116.9 km2 and an altitude of 918.7 m). The annual aver- age temperature is 14-15 °C, the annual rainfall is 50-55 mm, and the annual maximum evaporation is 2 788.2 mm. The annual total radiation is 6343 MJ·m-2 with 2889 sunshine hours. The accumulated tem- perature higher than 0 °C is 4700 °C on average; the accumulated temperature higher than 10 °C is 4278 °C; and the frost-free period is 180-200 days. The dominant wind direction is from the northeast, and the soil type is mainly yellow fluvial soil. The content of organic matter in the soil was 23.12 g·kg-1, alkali-hydrolyzable nitrogen 41.58 mg·kg-1, available phosphorus 16.1 mg·kg-1, and available potassi- um 196 mg·kg-1. In a 25-year-old Kuerlexiangli pear orchard, soil samples were collected under the can- opy (1.00 m away from the trunk), at the edge of the canopy (2.00 m away from the trunk) and outside the canopy (3.25 m away from the trunk) of the pear trees. The total and available contents of Mn and soil pH in 0-60 cm soil layer at different sampling points were analyzed. Pearson correlation analysis and one variable linear regression analysis were applied to analyze the relationship between spatial dis- tribution and availability of soil Mn and soil pH. The sampling depths were 0-5 cm, >5-10 cm, >10-20 cm, >20-30 cm, >30-40 cm, >40-50 cm, and >50-60 cm. The experiment was repeated 5 times, and 105 soil samples were collected in total. After the soil samples were brought back to the laboratory, they were air-dried, ground, sifted, mixed and bagged for using. Soil pH value was measured with an acidometer. Total manganese content in soil was determined with atomic absorption spectrophotometry. The content of available manganese in soil was determined by DTPA extraction - atomic absorption spectrometry.【Results】The soil pH value of the orchard varied from 8.25 to 8.90, with an average val- ue of 8.60. The soil was alkaline and pH increased with soil depth. The soil pH at different sampling points followed an order of outside canopy > within canopy > edge of the canopy. Compared with the soils outside and below the canopy, soil along the edge of canopy was of relatively weaker alkalinity, which may be related to long term fertilization application to the soil along the edge of the canopy. The total Mn content ranged from 680.08 mg · kg-1 to 824.68 mg · kg-1, with an average of 727.41 mg · kg-1. With the increase of soil depth, the total content of soil Mn increased first and then decreased, but there was no significant difference among different sampling points and different soil layers. The available Mn content varied from 4.86 mg · kg-1 to 13.19 mg · kg-1, with an average value of 8.44 mg · kg-1. The available content of soil Mn in the whole orchard was at medium level, and gradually decreased with the increase of soil depth. Although there was no significant difference in available content of soil Mn among different sampling points (below, at the edge of and beyond the canopy), it was significantly higher in the 0-20 cm soil layer than in the 20-60 cm layer, indicating that the distribution of soil Mn in the orchard was hierarchical and typically surface aggregated. The total Mn content in soil was not sig- nificantly affected by soil pH, but there was a significant correlation between soil available Mn content and soil pH (p < 0.01), and the soil available Mn content below the canopy, at the edge of the canopy or outside the canopy all showed a very significant negative linear correlation with soil pH, indicating that the available content of soil Mn gradually decreased with the increase in soil pH.【Conclusion】In the soil nutrient management in Kuerlexiangli pear orchard, reasonable fertilization and field management should be carried out according to the spatial distribution and availability of soil nutrients. In order to achieve efficient utilization of soil nutrients for fruit production with good quality, it is suggested to ap- ply physiologically acid fertilizer or increase the use of organic fertilizer to adjust soil pH and improve the availability of soil Mn.