Potassium management in potato production in Northwest region of China
Introduction
Potato is one of the main vegetable crops. China is now the world's largest potato (Solanum tuberosum L.) producer and the output has reached 93 million tons in 2012. The Northwest region of China is the main potato production region with a planting area of nearly 2 million ha and a total tuber production of 29 million tons, accounting for 36% and 31% of total area and production in China, respectively.
Potato is high K requirement crop. It takes up K in quantities much greater than those of N and P (Panagiotopoulos, 1995). On an average, potato removed about 91 kg K2O ha−1 at the yield of 29 Mg ha−1 (Moinuddin et al., 2005). Duan et al. (2013) found that the average uptake of K by rainfed potato and irrigated potato in Inner Mongolia of China was 82.2 and 221.7 kg K2O ha−1 at the yield of 14.9 and 35.7 Mg ha−1, respectively. Potassium is a quality element. The positive effect of K fertilization is greater on tuber quality than on yield (Kavvadias et al., 2012). Potassium is partially responsible for light-colored chips characteristic through a positive influence on lowering the sugar, amino acid, and tyrosine content in potatoes, which tend to darken the chips (Wilcox et al., 1968, Cummings and Wilcox, 1968). It also plays an important role for maintaining tone and vigor of the plants.
Farmers traditionally applied nitrogen (N) and phosphorus (P) fertilizers but neglected K fertilizer in potato production of Northwestern China, due to a conception of sufficient soil K in this region. As a result, potato plants acquired K from native soil, leading to mining of soil K reserves and decrease of soil K supply, adversely affected tuber yields/quality (Khan et al., 2012). There is great potential to improve both yield and quality of potato to a great extent with balanced use of N, P and K. However, farmers did not know how much K should be applied due to lack of scientific information and method for K recommendations.
The commonly used methods for K recommendations for crops are based on soil testing and sometimes can be used effectively for guiding fertilizer applications (Hannan et al., 2011), but the critical level of soil test K should be determined. The alternative way is to make fertilizer recommendation based on yield response and agronomic efficiency, which was successfully used in fertilizer recommendation for wheat and maize (Chuan et al., 2013, Xu et al., 2014). Another method for K recommendation is based on K balance in soil plant systems and the recommended rate of K should be at least the amount of K removed by crop products.
However, information on yield/quality response to K application, K use efficiency, soil K supply and productivity, the relationship between potato tuber yield and plant uptake K and the critical level of soil test K in potato systems are not available. The purpose of this study is to: (1) determine agronomic and economic response of potato to K application, (2) determine supply capacity of soil K and the critical level of soil test K, (3) establish scientific basis for K recommendation for potato production.
Section snippets
Field trials
Total of 192 field trials were conducted in farm's fields during 2003–2013 in Inner Mongolia, Gansu, Qinghai and Ningxia provinces, the main potato production regions in Northwest China. The sites and number of trials were listed in Table 1. Each trial had two treatments: (1) Nitrogen, phosphorus and potassium (NPK); (2) Nitrogen and phosphorus (NP). The amount of N, P2O5 and K2O applied was recommended based on Agro Services International (ASI) systematic approach (Hunter, 1980, Portch and
Tuber yield response to K application
Potassium application significantly (P < 0.001) affected tuber yield compared with treatments without K fertilization (Table 3). The average yield response was 3.2 Mg ha−1 with a range from −2.8 to 7.2 Mg ha−1. Frequency distribution indicated that about 90% of the trials showed positive response to K application and 44.8% (n = 192) was less than 2 Mg ha−1, 36.5% was in 2–4 Mg ha−1 and 18.8% was more than 5 Mg ha−1 (Fig. 1a). Other studies also showed significant tuber yield response to K fertilization (
Conclusions
Application of K fertilizer increased potato tuber yield in 90% of the observations by an average of 3.2 Mg ha−1, increased commercial tuber rate, mean tuber weight and starch content, reduced sugar content. The average AEK was 30.2 kg tuber kg−1 K2O and the average net income through K application was US$ 715 ha−1. At current K application levels, soil K was mined in nearly 80% of the observations. Soil exchangeable K could explain 25% and 30% of variation for IKS and IKP. There were significant
Acknowledgement
The authors thank the International Plant Nutrition Institute (IPNI) for the financial support. The Contribution of Professor Li Youhong from Ningxia Academy of Agricultural Sciences and Professor Chen Zhanquan from Qinghai Academy of Agricultural Sciences are greatly appreciated.
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