Objectives Effects of long-term application of organic manure and chemical fertilizers on yield and the use efficiency of deep layer soil water in rain-fed apple orchards in Weibei Highland were studied.
Methods WinEPIC model was applied to quantitatively simulate the dynamic response of apple yields, soil water contents in 0–15 m soil layer and the contents of soil organic carbon with 6 combinations of organic manure and chemical fertilizers in the apple orchard of Luochuan during the period from 1965 to 2009. On the base of total input of N 360 kg/hm2 and P2O5 180 kg/hm2, six ratio of pig manure addition treatments were designed as following: M0 (chemical fertilizer), M1 (1/5 decomposed pig manure), M2 (2/5 decomposed pig manure), M3 (3/5 decomposed pig manure), M4 (4/5 decomposed pig manure), and M5 (single decomposed pig manure). The orchard apple yields, the organic carbon and available water contents in the 0–15 m depth of soil layer were investigated in November of each year; the simulated values were correlated with the observed values, and its long-term dynamics were simulated with the model.
Results Through establishment of the local database, revision of apple growth parameters and model verification, the WinEPIC model can accurately simulate responses of apple yields and soil water use in apple orchards with different fertilization treatments in Luochuan, and can be used to simulate water productivity of apple orchards under different fertilization treatments in Weibei Highland. During the simulation study period of 1965 to 2009, with the increase of tree age, the apple orchard yield showed a trend that increasing rapidly in the early stage and reducing fluctuantly later; meanwhile, the soil moisture content showed a fluctuant downward trend and soil organic carbon content revealed an increasing tendency. Compared with M0, the apple orchard yields of other five treatments were increased by 5.2%, 9.8%, 10.3%, 1.3% and –6.6% respectively. The apple yield of M3 was the highest among the five treatments, and the average annual apple yield in 42 years production period was 30.98 t/hm2. The increase rates of soil available water contents were respectively 4.3%, 6.2%, 5.9%, 9.0% and 9.8%, the water storage of M5 was the largest, and the 45 years average soil moisture content in the 0–15 m layer was 1339 mm. The vertical soil moisture contents in the apple orchards changed severely in the 0–15 m layer under the six treatments, the time that soil-drying layer occurred on apple orchards was respectively 13 year-old, 14 year-old, 15 year-old, 15year-old, 16 year-old and 16 year-old, and the dried layers of apple orchards all reached at 11m. The average values of soil organic carbon contents during 45-year growth period in 0–500 cm soil layer of apple orchards under the 6 fertilization treatments were 6.43, 7.68, 7.97, 8.67, 8.71 and 8.78 g/kg, raising with the increase of the proportion of organic manure application. The soil organic carbon contents of M1, M2, M3, M4 and M5 were respectively increased by 19.4%, 24.0%, 34.8%, 35.4% and 36.4% compared with M0. Under different fertilization treatments, the soil water contents were significantly and negatively correlated with the orchard land use age, on the contrary, there was a positive correlation between the soil organic carbon contents and the orchard land use age, and the two correlation coefficients became larger with the increase of the proportion of organic manure use.
Conclusions Compared with single chemical nitrogen fertilizer application, the 5 organic manure fertilizer treatments were all favorable for the increases of soil moisture contents and soil organic carbon contents, and the 4 treatments of M1–M4 could improve apple orchard yields in some degree. Considering the soil available water content in 0–15 m soil layer and simulated apple orchard yields from 4 to 45 years old, and the N application of 360 kg/hm2, the appropriate proportion of organic manure and chemical fertilizer for Luochuan apple orchard is among 4∶6 to 6∶4.
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