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Many previous studies have shown that land use patterns are the main factors influencing soil infiltration. Thus, increasing soil infiltration and reducing runoff are crucial for soil and water conservation, especially in semi-arid environments. To explore the effects of agroforestry systems on soil infiltration and associated properties in a semi-arid area of the Loess Plateau in China, we compared three plant systems: a walnut (Juglans regia) monoculture system (JRMS), a wheat (Triticum aestivum) monoculture system (TAMS), and a walnut-wheat alley cropping system (JTACS) over a period of 11 years. Our results showed that the JTACS facilitated infiltration, and its infiltration rate temporal distribution showed a stronger relationship coupled with the rainfall temporal distribution compared with the two monoculture systems during the growing season. However, the effect of JTACS on the infiltration capacity was only significant in shallow soil layer, i.e., the 0–40 cm soil depth. Within JTACS, the speed of the wetting front’s downward movement was significantly faster than that in the two monoculture systems when the amount of rainfall and its intensity were higher. The soil infiltration rate was improved, and the two peaks of soil infiltration rate temporal distribution and the rainfall temporal distribution coupled in rainy season in the alley cropping system, which has an important significance in soil and water conservation. The results of this empirical study provide new insights into the sustainability of agroforestry, which may help farmers select rational planting patterns in this region, as well as other regions with similar climatic and environmental characteristics throughout the world. [ABSTRACT FROM AUTHOR]

Highlights • Nitrous oxide emissions were higher in the apple orchard than in the wheat field. • Summer rainfall and winter snowfall were the principal controllers of N 2 O fluxes. • A moisture threshold associated with rainfall triggered higher N 2 O emissions. • Nitrous oxide emission due to land use change was altered by precipitation in arid region. Abstract The conversions of cropland to forest, or other tree-based systems, are considered to be important processes affecting regional and global greenhouse gas budgets, especially for nitrous oxide (N 2 O). From April 2007 to March 2009, in the rain-fed semi-arid climate of the Loess Plateau, China, soil N 2 O emissions were measured using static chambers from a winter wheat field and an apple orchard, which had been established in part of the wheat field 23 years earlier.Annual average N 2 O emissions from the apple orchard (2.40 kg N 2 O ha−1yr−1) were 12.15% higher than those in the wheat field (2.14 kg N 2 O ha−1yr−1). Seasonal rainfall, in combination with higher nitrogen fertilization, had a promoting effect on N 2 O emissions in the apple orchard compared with the wheat field. The amounts and patterns of summer rainfall and winter snowfall were the principal controllers of seasonal and annual N 2 O fluxes in these rain-fed semi-arid regions, likely through their influence on soil moisture content. Since there may be a moisture threshold associated with summer rainfall and winter snowfall triggering higher N 2 O emissions, climatic regimes should be taken into account when assessing the effects of land use on N 2 O emissions in the Loess Plateau. [ABSTRACT FROM AUTHOR]