Effects of Soil Properties and Depth on Fruit Tree Chlorosis in the Loess Region in Northern China

Abstract

The loess region in northern China is an important area of apple (Pyrus malus L.) and pear (Pyrus communis L.) production due to its favorable soil and climate. In recent years, as the apple and pear production in this region rapidly increased, more orchards experienced iron deficiency chlorosis. However, information on soil nutrient status and fruit tree chlorosis of this region is scarce. In this research, we collected soil and fruit tree leaf samples from 25 pear and apple orchards (10 chlorotic orchards and 15 nonchlorotic orchards). Soil samples were collected at depths of 0–20 cm, 20–40 cm, 40–60 cm, and 60–80 cm. Soil organic matter, total nitrogen (TN), alkali‐hydrolyzable N, Olsen‐phosphorus (P), ammonium acetate‐potassium (K), DTPA‐iron (Fe), and less than 0.01‐mm soil particle content were analyzed, soil bulk density of 0–10 cm, 10–20 cm, 20–30 cm, and 30–40 cm were also determined. Leaf samples were analyzed for chlorophyll content. Comparison of soil properties was performed between chlorotic orchard soils and nonchlorotic orchard soils; stepwise multiple regression was performed between leaf chlorophyll content and soil properties. The results indicated that those orchard soils were rich in P and K but deficient in Fe. Chlorotic orchard soils contained more K, bicarbonate and less than 0.01‐mm soil particles, and less DTPA‐Fe in certain layers than those of nonchlorotic orchard soils. Leaf chlorophyll content negatively correlated with soil bicarbonate, alkali‐hydrolysable N, and ammonium acetate‐K and positively correlated with TN, DTPA‐Fe, and bulk density at certain depths. Most of these soil properties that have a significant difference between these two kinds of orchard soils or affect leaf chlorophyll content occur below 40 cm in the soil profile. These results suggested that high bicarbonate content and low available Fe content in soils were the primary causes for fruit tree chlorosis in the loess region. Shallow groundwater table in the chlorotic orchards and root growth impairment in the surface soil because of tillage are supposed to be the reason why deeper depth in soil profile play an important role in fruit tree chlorosis in this region.