Interactive effect of irrigation and blend ratio of controlled release potassium chloride and potassium chloride on greenhouse tomato production in the Yellow River Basin of China
Introduction
Tomato (Solanum lycopersicum L.) is one of the most popular vegetables cultivated worldwide, which has rich in lycopene, vitamins, amino acid, organic acids, antioxidants, and minerals (Savić et al., 2008, Erba et al., 2013). World demand for tomatoes increases annually, creating considerable space for tomato cultivation (Lahoz et al., 2016). The Yellow River Basin is the largest greenhouse tomato planting area in China, which plays an essential role in the supply of fresh tomatoes (Bao and Li, 2010). However, with the widespread planting of greenhouse tomatoes, a variety of adverse effects followed. The economic benefits of greenhouse tomato cultivation drive farmers to use irrigation water and fertilizers in large quantities to achieve higher yields, which results in a series of problems, such as wasting agricultural water and fertilizer resources, undermining tomato yield, and causing economic and environmental problems (Li et al., 2017b, Li et al., 2017a). Meanwhile, with global challenges imposed by the increasing population and the negative impacts of climate change, agricultural water shortages are becoming more frequent (Ye et al., 2015). Therefore, a reasonable irrigation and fertilization strategy that reduces water and fertilizer resources waste, improves water and fertilizer production and maintains yield is needed.
Drip irrigation is one of the most popular water-saving irrigation techniques in the world, which provides the required quantity of water directly to the root zone of plants (Mattar et al., 2020). Drip irrigation is superior to traditional furrow irrigation in improving water use efficiency (WUE) and saving agricultural water resources, with ideal effects on large-area planting (Choudhary et al., 2010). However, as the most common irrigation method in greenhouse vegetable planting in China, furrow irrigation is widely used, especially in economically backward areas (Mohammadi et al., 2019). The small area family planting model makes the high investment of drip irrigation technology unable to be accepted by farmers. Therefore, there is an urgent need for economic and simple irrigation technology to meet the requirement of farmers for water-saving irrigation. In the last few decades, deficit irrigation has been proposed with the consideration of water shortage in the Yellow River Basin, which is the important water-saving irrigation strategy in semi-arid areas (Yuan et al., 2019, Li et al., 2010). Deficit irrigation is a suitable method with less investment and simple operation, which has the characteristics of saving agricultural water and improve WUE (Zou et al., 2020, Ma et al., 2019). It’s a practice that makes plants tolerate or resist drought stress by reducing irrigation during the entire crop cycle or by withdrawing irrigation at certain stages (Sun et al., 2014). Deficit irrigation has been proved to increase tomato fruit quality and WUE (Cantore et al., 2016, Wang et al., 2015). A previous study on tomatoes demonstrated that when the irrigation amount was reduced by 50% at the ripening stage, the irrigation amount could be saved by 30.4%. However, yield penalty due to drought stress under deficit irrigation has frequently been noticed in different crop species including tomatoes (Agbna et al., 2017). Lu et al. (2019) analyzed 25 research articles with 561 experimental groups found that deficit irrigation decreased tomato yield with a mean difference of 18.6 t ha-1. Meanwhile, compared with conventional irrigation, deficit irrigation significantly reduced tomato leaves stoma conductance and photosynthetic rate (Akhtar et al., 2014). Reducing irrigation amount while maintaining a high tomato yield is required for the sustainable development of agriculture (Cui et al., 2020). Previous studies have shown that water and nutrient may interact with each other to produce a coupling effect (Pan et al., 2017). Therefore, formulating an appropriate fertilization strategy to offset the negative impact of deficit irrigation on tomato growth and yield is a necessary condition to improve its applicability and sustainability.
Potassium (K) is the most essential and abundant inorganic cation in the plant, which can make up 10% of plant dry weight. It is a primary cellular osmotic regulation substance and plays an imperative role in plant water relations, and is involved in numerous physiological processes related to plant tolerance drought stress, including stomatal movement, turgor pressure maintenance, cytosolic pH homeostasis, and etc. (Tavakol et al., 2018, Zhang et al., 2019, Zahoor et al., 2017). Previous studies show that K fertilizer application enhanced photosynthetic rate, plant growth, and drought resistance under water stress (Egilla et al., 2001). Meanwhile, the role of K in osmotic regulation promotes the accumulation of more K ions in plant tissues and enhances the water acquisition by plants under drought stress (Zhang et al., 2019). In recent years, the importance of K in crop yield has been and reported (Pervez et al., 2004). Zain and Ismail (2016) reported that the application of potassium alleviated the negative effect of drought on crops and improved crop yield and drought resistance. This knowledge has stimulated substantial K fertilizer application in tomatoes cultivation, resulting in leading to reducing KUE, unbalancing nutrient supply, increasing environmental pollution risk, and decreasing tomato fruit quality by enhancing the incidence of blossom-end rot (Ju et al., 2007, Chen et al., 2017, Liu et al., 2011). Based on the large scale of vegetable production and the excessive application rate of potassium fertilizer in China (20.9 million ha and 5.6 million t in 2019; China Statistical Yearbook 2019), appropriate K fertilizer management is urgently needed to ensure optimum crop yields and the conservation K fertilizer resources. The controlled-release potassium chloride (CRK), as a novel environmentally friendly K fertilizer, was coated with a polymer (a biobased polyurethane polymer). It can reduce the fertilizer particle contact with soil and water and has advantages of high KUE, low labor input and time saving (Yang et al., 2017) when CRK usually was applied once. Previous studies showed that polymer-coated potassium chloride application promoted tomato plant growth and increased tomato yield, quality, water use efficiency (WUE), and KUE compared with potassium chloride (KCl) application (Qu et al., 2020). Although CRK has many advantages, it still has some problems, such as the slow release of potassium at the early stage of application, which cannot meet the K demand of crop seedlings. Furthermore, the high manufacturing cost of CRK makes it difficult to be widely used. To make up for the shortcomings of the CRK application, the problem of slow initial release and high price can be solved by mixing CRK with KCl in a particular proportion. Yang et al. (2017) reported that the release rate of CRK and KCl compound had the characteristics of synchronization with cotton plants nutrient uptake in the whole growth period and increased cotton yield and quality compared to CRK. Meanwhile, fertilizer prices and labor costs have fallen sharply. Therefore, CRK and KCl compound has great potential for decreasing input and increasing crop yield, quality, net come, and KUE.
Both water and fertilizer are considered to be the most important and manageable environmental factors affecting crop growth. Effective water and K fertilizer management strategy are essential to guarantee the WUE and KUE as well as maintain yield. Hence, for the sake of improving irrigation efficiency and reducing the yield and environmental damage caused by excessive K fertilizer application in the process of tomato planting. Two years of pot experiments were conducted in this study to learn the best combination of different irrigation levels and the proportion of CRK mixed with KCl to maximize the synergy under the 40% K application rate reduction conditions. The purposes of this experiment are1) to explore the tomato plant growth and fruit yield response to different irrigation levels and CRK to KCl blending ratio; 2) to find an optimum assembly of water and K fertilizer to maximize tomato fruit yield and quality; 3) to establish reasonable water and potassium management strategy for the greenhouse tomato cultivation in the Yellow River Basin of China.
Section snippets
Site, experiments and cropping details
A tomato pot experiment was conducted during two consecutive growing seasons (Apr. 26, 2020-Aug. 27, 2020 and Apr. 8, 2021-Aug. 1, 2021) in a greenhouse at Shandong Agricultural University, China. The soil (from 0 to 20 cm deep in a plowed field at the science park area of the south campus of Shandong Agricultural University) used in the pot experiment was classified as Typic-Hapli-Udic Argosols according to the Chinese Soil Taxonomy (CRGCST, 2001) and Typic Hapludalf according to the United
K release characteristics of the CRK and CRK-KCl mixtures
The release characteristics of the nutrient are the key evaluation indicators of controlled release fertilizer field application performance. The K release rate of CRK and CRK-KCl mixtures are mainly significantly affected by soil water content. Within a certain range, the K release rate of CRK and CRK-KCl mixtures increase with the increases in soil water content (Fig. 3). For 100% CRK, during the first 21days, 15.1%, 11.8%, and 8.3% of total K were released from CRK in the W100, W80, and W60
Discussion
Tomato is an important vegetable that demands a lot of water (Li et al., 2021). As the only source of soil water for greenhouse tomatoes, irrigation has a great impact on tomato yield, quality and water-fertilizer use efficiency (Chen et al., 2014). The result of the present study showed that tomato yield and KUE increased significantly with the increase of irrigation amount. Maximum yield and KUE (2777.1 g pot-1 and 57.8% in 2020 and 2992.9 g pot-1 and 62.0% in 2021, respectively) occurred in
Conclusions
This study showed that irrigation level and CRK to KCl blending ratio strategies had an obvious interaction on tomato yield, quality, and water-K use efficiency. Under the interactive effect of 80% irrigation level-80% CRK and 20% KCl mixtures combination, the soil available K supply was consistent with the demand of tomato in the process of greenhouse tomato. Furthermore, the ABA and CTK contents, H2O2 and MDA contents in leaves and roots, and the rubisco and osmotic regulation substances
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The research was funded by the National Key Research and Development Program of China (2016YFD0201202).
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