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Trends in grain yields and soil organic C in a long-term fertilization experiment in the China Loess Plateau

Fan, Tinglu, Xu, Minggang, Song, Shangyou, Zhou, Guangye, Ding, Linping
Zeitschrift für Pflanzenernährung und Bodenkunde 2008 v.171 no.3 pp. 448-457
Triticum aestivum, Zea mays, arid lands, carbon sequestration, corn, grain yield, loess, nutrients, phosphorus fertilizers, plateaus, roots, single nucleotide polymorphism, soil, soil organic carbon, straw, weather, wheat, China
Changes in grain yields and soil organic carbon (SOC) from a 26 y dryland fertilization trial in Pingliang, Gansu, China, were recorded. Cumulative C inputs from straw and root and manure for fertilizer treatments were estimated. Mean wheat (Triticum aestivum L.) yields for the 18 y ranged from 1.72 t ha⁻¹ for the unfertilized plots (CK) to 4.65 t ha⁻¹ for the plots that received manure (M) annually with inorganic N and P fertilizers (MNP). Corn (Zea mays L.) yields for the 6 y averaged 2.43 and 5.35 t ha⁻¹ in the same treatments. Yields declined with year except in the CK for wheat. Wheat yields for N only declined with time by 117.8 kg ha⁻¹ y⁻¹ that was the highest decrease among all treatments, and that for NP declined by 84.7 kg ha⁻¹ y⁻¹, similar to the declines of 77.4 kg ha⁻¹ y⁻¹ for the treatment receiving straw and N annually and P every second year (SNP). Likewise, the corn yields declined highly for all treatments, and the declined amounts ranged from 108 to 258 kg ha⁻¹ y⁻¹ which was much higher than in wheat. These declined yields were mostly linked to both gradual dry weather and nutrients depletion of the soil. The N only resulted in both P and K deficiency in the soil, and soil N and K negative balances in the NP and MNP were obvious. Soil organic carbon (SOC) in the 0-20 cm soil layer increased with time except in the CK and N treatments, in which SOC remained almost stable. In the MNP and M treatments, 24.7% and 24.0% of the amount of cumulative C input from organic sources remained in the soil as SOC, but 13.7% of the C input from straw and root in the SNP, suggesting manure is more effective in building soil C than straw. Across the 26 y cropping and fertilization, annual soil-C sequestration rates ranged from 0.014 t C ha⁻¹ y⁻¹ for the CK to 0.372 t C ha⁻¹ y⁻¹ for the MNP. We found a strong linear relationship (R² = 0.74, p = 0.025) between SOC sequestration and cumulative C input, with C conversion-to-SOC rate of 16.9%, suggesting these dryland soils have not reached an upper limit of C sequestration.