The Soil Calcium Evolutionary Trend In Weibei Apple Orchards And Its Effects On Apple Fruit Quality

Calcium is one of the most essential nutrients affecting tree health and fruit quality.It is irreplaceable in delaying fruit senescence,improving fruit storage properties and controlling fruit quality.Affected by the factors such as apple fruit’s particular physiological demand of calcium,tree root exudates and the orchard management level,large quantity of calcium carbonate in orchard soil is dissolved and absorbed,thus the availability of calcium is significantly dropped.As a result,physicological diseases such as bitter pit and watercore occur,and tree canker and early defoliation are prevalent,which causes tree aging and declines the apple fruit yield and quality.All these significnatly hinder the healthy and sustainable development of apple industry in Weibei area.In view of the ecological environment and the lack of research on Weibei orchard soil management,this investigation was carried out with an aim to prevent and control the orchard soil calcium degradation and maintain the healthy and sustainable development of apple industry by using the theories and methods of Soil Science,Agrogeology and Plant Nutrition.Soil profile samples,tree leaf samples and fruit samples were collected from the main apple production areas Luochuan and Baishui in Weibei area.This investigation systematically studied the temporal-spatial variation features of soil calcium carbonate,water-soluble calcium and exchangeable calcium under different conditions such as region,orchard age,soil depth,planting pattern,fertilizing method and sampling site,and their effects on fruit quality and tree health.The variation features of orchard soil organic matters,pH and soil compaction and their correlation with soil calcium were also discussed.The major findings are listed as follows.(1)Calcium carbonate was the calcium store for calcareous soil in Weibei area.The content of and stock of calcium carbonate in 0~100 cm soil depth in Weibei orchards decreased significantly with the increase of orchard age,while increased with the increase of soil depth.The decrease of calcium carbonate was most significantly shown in the orchards with more than 25 years of plantation and in the 0~30 cm soil depth.The total stock of calcium carbonate in Luochuan orchards plummeted with the increase of orchard age;while in Baishui,it decreased significantly in orchards with more than 25 years of plantation.The content and stock of calcium carbonate in Baishui orchards were both higher than those in Luochuan orchards.Long-term plantation and the application of chemical fertilization caused significant degradation of calcium carbonate in 0~100 cm soil depth.The calcium carbonate content in orchard soil was significantly lower than that in farmland soil.The combined application of chemical fertilizer and farmyard manure could slow the decline of soil calcium carbonate,which was very important to maintain the stable soil calcium supply to the orchard root zones.The annual uptake of calcium from soil owing to fruit production,clearing up leaves and pruning was around 152.15~191.26 kg/hm~2,amounting to consuming 380.38~478.15 kg/hm~2 of soil calcium carbonate.And the calcium contained in the large quantity of fruit sold elsewhere could not contribute to the local biolcycle.(2)Water-soluble calcium was the most easily absorbed soil calcium but it was also vulnerable to leaching.Water-soluble calcium content in Weibei orchards ranged between 0.074 and 0.605 g/kg,the average value being 0.201 g/kg.More than 70% of it was distributed between 0.1~0.3 g/kg.The content and stock of soil water-soluble calcium in Luochuan orchards decreased significantly with the increase of orchard age,while increased with the increase of soil depth.The water-soluble calcium content in Baishui orchards demonstrated alternate change from high to low with the increase of orchard age,while decreased with the increase of soil depth.The water-soluble calcium content in 0~30 cm soil depth varied greatly.The water-soluble calcium content in 0~30 cm orchard soil depth(fertilizer coating)decreased more significantly than farmland soil because of long-term tree plantation.Long-term application of chemical fertilizer and the absorption and utilization of calcium by the root system were the main reasons for the degradation of soil water-soluble calcium.The average water-soluble calcium content in the soil 1.5 m from the tree trunk was lower by 22.4% than that at a site 1.0 m from the tree.In 0~40 cm soil depth,the difference between the two was significant.Both orchard soil calcium carbonate content and organic matter content are at significant exponential function with water-soluble calcium.The accumulation of root exudates accelerated the dissolution of calcium carbonate and increased the soil water-soluble calcium content.Meanwhile this also increased the risk of calcium migration.(3)Soil calcium supply capability was directly related to not only the exchangeable calcium content but also the soil calcium saturation.The average exchangeable calcium content in 0~100 cm soil depth was 3.789 g/kg,more than 56% of which distributed 3.5~4.0 g/kg.The orchard soil exchangeable calcium content in Weibei Region increased slowly with the increase of soil depth.It decreased slowly with the increase of orchard age in orchards with less than 25 years of plantation;in orchards with more than 25 years of plantation it decreased greatly.This variation was more noticeable in Luochuan orchards.The exchangeable calcium stock first increased and then decreased with the increase of orchard age and it generally increased with the increase of soil depth.The soil calcium saturation was lower than the threshold(60%)in 0~100 cm whole soil profile of Weibei orchards with more than 25 years plantation.Luochuan orchard soil calcium saturation decreased significantly with the increase of orchard age,while Baishui orchards were faced with calcium supply obstacles.The exchangeable calcium content in 0~100 cm orchard soil depth decreased significantly compared with farmland soil.The soil exchangeable calcium content decreased significantly in the orchards only applying chemical fertilizer,compared with those applying both chemical fertilizer and farmyard manure.The soil exchangeable calcium content was lower at the site 1.5 m from the tree trunk than that was 1.0 m from the tree.The orchard soil exchangeable calcium content was in a small positive correlation with calcium carbonate content and water-soluble calcium content.This proved that long-term heavy application of chemical fertilizer tampered with the balance of transformation among different types of calcium in calcareous soil,thus the soil calcium was significantly degraded.(4)Aggregative indicator method was adopted to analyze fruit quality under different orchard ages,cultivars and regions.The results showed that fruit quality in Weibei apple optimized zones was unstable.“Relatively stable optimal fruiting period” was only confined to orchards with 16~25 years of plantation,during which period,the quality of Fuji apple was the best.The fruit quality in orchards with more than 25 years of plantation came next,while those with less than 15 years of plantation produce fruit of low quality.The Fuji apple was obviously better in overall quality than Gala and Qinguan,while Gala was better than Qinguan.Luochuan Fuji apple was better than Baishui apple in appearance,while the latter was better in inner quality.These two cultivars both could meet the requirements for the physicochemical indexes of Super Fuji.With the increase of orchard age,the single weight and single volume of Fuji apple increased significantly.In full bearing period(16~25 a),the single weight and single volume remained stable.Specific gravity of fruit in orchards under different ages proved to be of little difference with the increase of orchard age,while soluble solid content showed significant difference.With the increase of orchard age,fruit hardness declined slowly;the titratable acid content first increased and then decreased;calcium content first decreased and then increased.The soil calcium carbonate content,water-soluble calcium content and exchangeable calcium content were all in significant positive correlation with Fuji fruit hardness.The dramatic degradation of Fuji apple fruit quality was related to soil calcium decline.(5)Orchard soil organic matter was essential to soil fertility.It was also an important guarantee of the sustainable development of Weibei apple industry.The average soil organic matter content in 0~40 cm Weibei orchard soil depth was 11.79 g/kg,more than 85% of which was at a relatively low level of less than 15 g/kg.This low level of soil organic matter content could not reach the standard required of the high-yield and high-quality orchard soil and the green food base soil.Between 1982 and 2012,Weibei orchard soil organic matter content generally showed a tendency of first decreasing,then increasing and then slowly decreasing.During the 30 years,the average soil organic matter content in the arable layer increased only by 1.5 g/kg.The organic matter content in 0~100 cm soil depth increased with the increase of orchard age,and decreased with the increase of the soil depth,and the decrease was particularly dramatic in 0~40 cm soil depth.Generally,the organic matter content in Baishui was higher than Luochuan.In orchards with long-term application of chemical fertilizer,the soil organic matter content in 0~100 cm soil depth decreased by 19.9% than those with combined application of farmyard manure and chemical fertilizer.Therefore,the inadequate use of farmyard manure was the main cause of the slow increase of soil organic matter content and the deterioration of soil calcium degradation in Weibei orchards.(6)Calcium carbonate is a buffer matrix of soil pH as well as one of the important characteristics of calcareous soil.The average pH in 0~100 cm soil depth in Weibei orchards was 8.15,more than 80% of which distributed 8.0~8.5.According to the data of soil pH from the 2nd National Soil Survey,during the 30 years apple tree plantation,the average soil pH decreased by 0.3 units.The pH in 0~100 cm soil depth first increased and then decreased with the increase of soil depth.And it significantly decreased with the increase of orchard age.In the 0~20 cm soil depth of orchards with more than 20 years of plantation,soil pH dropped to lower than 8.The pH of Luochuan orchard soil was generally higher than that of Baishui orchards.Long-term apple tree plantation caused the pH in 0~100 cm soil depth to decrease by 0.16 units than compared with farmland soil.The apple orchard pH significantly correlated with soil water-soluble calcium content and exchangeable calcium content.This proved that soil acidity accelerated the dissolution of calcium carbonate,and increased the supply of active calcium to orchard soil.This effect was helpful for apple tree to absorb and utilize calcium,but it also accelerated the leaching and accumulation of soil calcium in deeper soil depths.This strong sign of soil calcium degradation could pose hidden trouble for the sustainable development of apple orchards.(7)As an aerogel material,calcium carbonate was a cementing agent of soil aggregate,affecting soil compactness.Weibei orchard soil compactness first decreased and then increased with the increase of orchard age,and it also increased with the increase of soil depth.The compactness reached maximum in 30~45 cm soil depth,amounting to more than 2000 kPa.There was no significant difference between Weibei orchards and farmland in soil compactness.This showed that orchard soil compaction was a kind of natural compaction caused by unstable soil aggregate.Soil in orchards with long-term application of chemical fertilizer was more compacted than those with combined application of chemical fertilizer and farmyard manure.This proved that the application of chemical fertilizer accelerated soil decalcification and damaged soil aggregate.It also indirectly confirmed that soil compaction was mainly caused by mobilization and accumulation of soil calcium and clay particles in deep soil depths.Weibei orchard soil compaction occurred in relatively deeper soil depths and was unlikely to be affected by natural processes such as alternate wetting and drying and alternate freezing and thawing.Therefore,its harm to the root system could last for a long time.