Long-term effects of potassium fertilization and straw return on soil potassium levels and crop yields in north-central China
Introduction
Potassium (K) is an essential nutrient and is involved in many important physiological processes in plants; it can improve crop quality and the ability of plants to survive adverse conditions (Marschner, 1995, Pettigrew, 2008). Sufficient K supply in soil helps to ensure high crop yield (Dong et al., 2010, Zhang et al., 2011). K deficiency is a world-wide problem, and the K levels in agricultural soils is decreasing across the globe (Fagerberg et al., 1996, Dobermann et al., 1998, Wijnhoud et al., 2003, Malo et al., 2005). In China, the majority of K fertilizer applied is imported, and soil K deficiency is recognized as one of the limiting factors for crop production (Zhang et al., 2008). The imbalanced fertilizer use in China led to a surplus or balanced situation for soil nitrogen (N) and phosphorus (P) but a serious depletion of K (Lin et al., 2006, Wang et al., 2008). Extending balance fertilization technology has enhanced K fertilizer input in crop production, but the increasing price of K fertilizer has increased agricultural production costs (Wang, 2012). Therefore, efficient use of K fertilizer is crucial for this resource limited nutrient.
Crop straw is an important organic fertilizer resource, especially for Li and Jin (2011) reported that China produced 8.1 × 108 t of crop straw in 2008, and this supplied 1.2 × 107 t of K2O. Therefore, straw retention in fields can return a considerable amount of plant K to the soil. In addition, straw retention could also decrease mineral N fertilizer losses by causing N immobilization in the short term, and increase carbon (C) sequestration in soil and enhance soil quality (Yadvinder-Singh et al., 2004, Plante et al., 2006, Liu et al., 2011). Recently, both wheat and maize straws return was widespread in winter wheat–summer maize rotation system in north-central China because the use of straw returning machine was increased in response to a ban by the Chinese government on field burning of crop straws. However, straw decomposition and nutrient release from straw were slow in the field, and the effects of straw return on crop yield, soil fertility and quality were not obviously shown in short term (Brunetto et al., 2011, Partey et al., 2011, Wang et al., 2010). Long-term field experiment could demonstrate the effects of different nutrient management strategies on crop yield, soil nutrient dynamics, and soil quality (Gong et al., 2009, Malhi et al., 2011, Liang et al., 2012). Several long-term experiments on fertilization and straw return treatments have been established in northern China, but these studies on changes in soil quality and nutrients mainly focused on topsoil, while few have focused on the deeper layers (Cao et al., 2008, Liu et al., 2010, Zhang et al., 2010, Zhang et al., 2011). Breulmann et al. (2012) indicated that research on the deeper soil layers could provide more information about soil nutrient properties. The objective of this study was to investigate the changes in soil K levels and crop yields under long-term K fertilization and straw return in north-central China.
Section snippets
Experimental site
Field experiment was conducted in October 1992 in fluvo-aquic soil (Calcaric Cambisols, FAO) at Malan farm (37°55′ N, 115°13′ E), Hebei province, north-central China. This region has a warm temperate, sub-humid continental monsoon climate. The annual mean temperature and precipitation are 12.5°C and 490 mm, respectively, and 70–80% of the annual precipitation occurs during the summer maize-growing season. The soil tested has a light loam texture with following properties in top 20 cm soils at the
Crop K uptake and soil K balance
Fertilization significantly affected wheat and maize K uptakes; however, experimental stage (five years as an experimental stage) only influenced maize K uptake (Table 1). Among the four treatments, annual wheat K uptake showed significant differences as: NP < NPS ≤ NPK ≤ NPKS in 1993–1997 and 1998–2002, NP < NPS < NPK = NPKS in 2003–2007 and 2008–2012. Annual maize K uptake in the same treatment increased with experimental time. The K uptake by maize in four treatments showed consistent trends as: NP < NPS <
Crop K uptake and soil K balance
The level of soil K supply significantly affected crop K uptake (Dobermann et al., 1998, Mallarino et al., 2012). In this study, annual wheat and maize K uptakes all increased with increasing K inputs (including fertilizer K and straw K) in the sequence of NP < NPS </≤ NPK ≤ NPKS. The NP, NPS, and NPK treatments resulted in negative annual soil K budgets due to total K inputs were lower than total K removal by crops from 1993 to 2007. Niu et al., 2011, Niu et al., 2013 also reported that the
Conclusions
Our study confirmed that K fertilization and/or straw return alleviated soil K depletion and enhanced soil K fertility, and high rate of K inputs enhanced their effects. Different fertilization strategies influenced soil available K and slowly available K mainly in the top 30 cm soil, and total K changed only in the 0–10 cm soil compared with the initial level. Straw return enhanced SOC, however, fertilization affected SOC mainly in the top 40 cm. K fertilization and/or straw return increased crop
Acknowledgements
This project was supported by the National Basic Research Program of China (973 Program) (2013CB127404 and 2013CB127405), the National Natural Science Foundation of China (31272243 and 31272245) and the International Plant Nutrition Institute (IPNI).
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