Multi-year average soil nutrient status at wheat and maize harvest, as affected by various treatments with fertilizer in a wheat-maize rotation system at Yucheng, Shandong Province of China (mean±standard error).

<p><i>P</i><0.05 between fertilizer treatments. For each crop, different letters within a column indicate a significant difference at </p

Grain yield of wheat (a) and maize (b) of different fertilizer treatments (Control, circle; NPK, triangle up; NP, triangle down; NK, square; PK, plus) under wheat-maize rotation system from 1994 to 2006 at Yucheng, Shandong Province of China.

<p>Grain yield of wheat (a) and maize (b) of different fertilizer treatments (Control, circle; NPK, triangle up; NP, triangle down; NK, square; PK, plus) under wheat-maize rotation system from 1994 to 2006 at Yucheng, Shandong Province of China.</p

Multi-year average grain yield of wheat and maize, as affected by various treatments with fertilizer in a wheat-maize rotation system at Yucheng, Shandong Province of China (mean±standard error).

<p><i>P</i><0.05 between fertilizer treatments. Different letters within a column indicate a significant difference at </p

Soil available N (a), Olsen-P (b) and available K (c) gap variation by N (SNG_N, soil available nutrient difference between NPK and PK plots, triangle up), P (SNG_P, the difference between NPK and NK plots, triangle down), K (SNG_K, the difference between NPK and NP plots, square) or NPK (SNG_NPK, the difference between NPK and Control plots, circle) fertilizer omission from 1994 to 2006 during wheat season at Yucheng, Shandong Province of China.

<p>Soil available N (a), Olsen-P (b) and available K (c) gap variation by N (SNG_N, soil available nutrient difference between NPK and PK plots, triangle up), P (SNG_P, the difference between NPK and NK plots, triangle down), K (SNG_K, the difference between NPK and NP plots, square) or NPK (SNG_NPK, the difference between NPK and Control plots, circle) fertilizer omission from 1994 to 2006 during wheat season at Yucheng, Shandong Province of China.</p

Yield gap variation of wheat (a) and maize (b) by N (GYG_N, the yield difference between NPK and PK plots in each year, triangle up), P (GYG_P, the difference between NPK and NK plots, triangle down), K (GYG_K, the difference between NPK and NP plots, square) or NPK (GYG_NPK, the difference between NPK and Control plots, circle) fertilizer omission from 1994 to 2006 at Yucheng, Shandong Province of China.

<p>Yield gap variation of wheat (a) and maize (b) by N (GYG_N, the yield difference between NPK and PK plots in each year, triangle up), P (GYG_P, the difference between NPK and NK plots, triangle down), K (GYG_K, the difference between NPK and NP plots, square) or NPK (GYG_NPK, the difference between NPK and Control plots, circle) fertilizer omission from 1994 to 2006 at Yucheng, Shandong Province of China.</p

Treatment and fertilizer nutrient rates (kg ha⁻¹) applied to winter wheat and maize at Yucheng, Shandong Province of China.

<p>Treatment and fertilizer nutrient rates (kg ha⁻¹) applied to winter wheat and maize at Yucheng, Shandong Province of China.</p

Seasonal variations in the CH₄ fluxes and the amount of irrigation for rice and vegetables (a) and the water depth under rice and daily precipitation from May 2012 to July 2013 (b).

<p>Seasonal variations in the CH₄ fluxes and the amount of irrigation for rice and vegetables (a) and the water depth under rice and daily precipitation from May 2012 to July 2013 (b).</p

Cumulative N₂O emissions under rice and vegetables with or without fertilization during the study period.

<p>Treatments are RF, rice with fertilization; NRF, rice with no fertilization; VF, vegetables with fertilization, and VNF, vegetables with no fertilization.</p

Results from the linear mixed model on the effects of land use and fertilization on the CH₄ and N₂O fluxes.

<p>Results from the linear mixed model on the effects of land use and fertilization on the CH₄ and N₂O fluxes.</p

Effects of Land-Use Conversion from Double Rice Cropping to Vegetables on Methane and Nitrous Oxide Fluxes in Southern China

<div><p>Compared with CO₂, methane (CH₄) and nitrous oxide (N₂O) are potent greenhouse gases in terms of their global warming potentials. Previous studies have indicated that land-use conversion has a significant impact on greenhouse gas emissions. However, little is known regarding the impact of converting rice (<i>Oryza sativa</i> L.) to vegetable fields, an increasing trend in land-use change in southern China, on CH₄ and N₂O fluxes. The effects of converting double rice cropping to vegetables on CH₄ and N₂O fluxes were examined using a static chamber method in southern China from July 2012 to July 2013. The results indicate that CH₄ fluxes could reach 31.6 mg C m⁻² h⁻¹ under rice before land conversion. The cumulative CH₄ emissions for fertilized and unfertilized rice were 348.9 and 321.0 kg C ha⁻¹ yr⁻¹, respectively. After the land conversion, the cumulative CH₄ emissions were −0.4 and 1.4 kg C ha⁻¹ yr⁻¹ for the fertilized and unfertilized vegetable fields, respectively. Similarly, the cumulative N₂O fluxes under rice were 1.27 and 0.56 kg N ha⁻¹ yr⁻¹ for the fertilized and unfertilized treatments before the land conversion and 19.2 and 8.5 kg N ha⁻¹ yr⁻¹, respectively, after the land conversion. By combining the global warming potentials (GWPs) of both gases, the overall land-use conversion effect was minor (<i>P</i> = 0.36) with fertilization, but the conversion reduced GWP by 63% when rice and vegetables were not fertilized. Increase in CH₄ emissions increased GWP under rice compared with vegetables with non-fertilization, but increased N₂O emissions compensated for similar GWPs with fertilization under rice and vegetables.</p></div