investigation of spatial variation pattern of superficial and deep soil properties on date palm yield (Case Study: Bushehr Province)

Introduction: Date palm (Phoenix dactylifera L.) is one of the most valuable domesticated fruit trees in Iran due to its significant importance in economy, societies, health benefits and production capacity in unfavorable semi-arid and arid regions. Iran has more than 30 million date trees on 216,000 hectares, which produce 900,000 tons of date products. Bushehr province is one of the main origins of dates and one of the producers of dates in the south of Iran. Considering the importance of dates in Bushehr province, this study was conducted with the aim of investigating the pattern of spatial changes in surface and deep soil characteristics and its effect on date performance.
Materials and methods: This research was carried out in an area of ​​39,000 hectares in Shabankare region located in Bushehr province in the south of Iran with old and new date gardens. First, the boundary of the study area was determined with satellite images obtained from the Google Earth program, then the target gardens were selected through the visual difference between the spread of tree crowns and the density of the garden as an indication of their growth ability. Field surveys were also conducted. Soil samples from three layers (0-30, 30-60 and 60-90 cm) were prepared from the soil of the desired gardens and analyzed in the laboratory. Soil properties such as texture, pH, extract electrical conductivity (EC), cation exchange capacity (CEC), equivalent calcium carbonate (CCE), percentage of organic carbon, high-use and low-use elements (nitrogen, phosphorus, potassium, iron, manganese, copper) , zinc), gypsum and saturation percentage. Date palm yield was obtained from three plants randomly in each garden, which were also asked about their garden's fertilizer and irrigation management. Descriptive analysis of measured data was done using SPSS software and also their correlation. Geostatistical analysis for soil properties and performance was performed by GS+ to study the spatial variation of the measured properties. Then the yield zoning was mapped as a result of the spatial variance of the studied production by the kriging estimator for the study area.
Results and discussion: Stepwise linear regression was calculated for soil properties with date yield in three soil depth layers (0-30, 30-60 and 60-90 cm). Adjusted R2 for layers was 0.24, 0.89 and 0.76 respectively. The highest correlation (0.89) was related to the second layer, which is known as the nutritional zone and has the highest ratio of primary and secondary roots to absorb nutrients from the soil solution. Only K has played a significant role in the regression equation of the first layer, which is called the respiratory zone, and most of its roots had negative geotropism and have a respiratory role. The highest Pearson's correlation coefficient (0.61) was obtained for macronutrient nitrogen due to the continuous vegetative growth stage in date palm. The correlation of yield with some soil properties such as pH, chalk, EC, CCE and sand was negative. More acidity of the soil causes stabilization of micronutrients. More gypsum and EC in soil tends to high osmotic pressure, which disrupts root water absorption. Sand has less water capacity and its high percentage in the soil causes water stress for plants.
Conclusion: Many parts of Iran are expected to be planted in the future due to climate changes and also the high tolerance of palm trees to environmental stresses, including drought and salinity. It is very important to have the correct information about the soil properties that can affect the performance of the palm tree. The soil layer between 30 and 60 cm is the best depth for good fertilization.