Effects of Combined Application of NPK Compound Fertilizer with Polyhalite Fertilizers on Peanut Yield, Nutrient Content and Partitioning in Henan Province, China

Abstract

China is the world-leading peanut (Arachis hypogaea L.) producer accounting for 35.93% of overall world production (in 2019), followed by India (13.80%) and Nigeria (9.13%). Within China, Henan is the leading peanut producing province producing 5.767 million metric tons in 2019, followed by Shandong and Guangdong regions with 2.848 and 1.087 million metric tons, respectively. Peanut is therefore an economically important crops in this province. The common fertilizer application practice in Henan province is dominated by NPK, which has been contributing to yield increments. However, the continuous application of the same nutrients over many years has resulted in unbalanced nutrient supply, and stagnant yield. Peanut, being a legume, meets most of its nitrogen requirement through nitrogen fixation. While it only requires a small rate of nitrogen (N) as a starter, an adequate supply of phosphorus (P), potassium (K), calcium (Ca), and sulfur (S) are essential to obtain higher yields and quality. Polyhalite is a sedimentary marine evaporate which consists of a hydrated sulfate of K, Ca and Mg with the formula: K₂Ca₂Mg(SO₄)₄·2(H₂O). Polyhalite contains 48% S and is being used in China as a source of K, S and other nutrients. The objective of this study in Henan, China, was to evaluate the effects of different polyhalite application rates on yield and nutrient content of different peanut plant parts at different growth stages. Eight fertilization treatments were tested: current practice (NPK) as the control, and seven combinations of NPK and polyhalite fertilizers. Results indicated that application of polyhalite in addition to the current practice produced higher leaf, stem and nut yields, and relatively higher nutrient contents at different growth stages. Highest leaf dry weight was obtained at 67 days after emergence (DAE) while highest stem and nut dry weight was obtained at 111 DAE. Different plant parts responded differently to different treatment combinations. Total leaf dry weight was the highest in T2 (NPK + 225 kg ha^–1 polyhalite) and lowest in T1 (control), the increase being 43%. Stem weight was the highest in T3 (NPK + 375 kg ha^–1 polyhalite) and lowest in T5 (NPK + 375 kg ha^–1 Sofipoly). T3 gave 37.8% more stem total dry weight yield over T5 and 20% more over the control (T1). Similarly, total nut yield was highest in T6 (90% NPK + 375 kg ha^–1 polyhalite) and lowest in T7 (80% NPK + 375 kg ha^–1 polyhalite). T6 yielded 28.9% more yield over T7 and 27% more yield over the control (T1). Application of NPK with 375 kg ha^–1 polyhalite gave higher stem dry weight while application of 70% NPK with 375 kg ha^–1 polyhalite gave the lowest dry matter yield indicating that optimum application of NPK is required to benefit from nutrients from polyhalite application. However, further multi-location and multi-year experiments are required to make optimum rate recommendations. Economic analysis of the fertilizer combinations is also required.

Keywords: Peanut; Fertilizer; Polyhalite; Growth stage; Plant parts.

Introduction

Peanuts (Arachis hypogaea), also referred to as groundnuts, are an annual herbaceous legume with an indeterminate growth habit. As these alternate names imply, this unique plant produces its fruit (peanut) below ground. Peanut is an economically important oilseed, feed, and food crop and widely cultivated in tropical and subtropical regions of the world. Although a legume; it is generally included amongst the oilseeds due to its high oil content. Peanuts are rich in protein, oil, and fibers (Suchoszek-Lukaniuk et al., 2011). For human consumption, the crop is cultivated primarily as whole seeds or as a processed product. Peanuts are key oilseed and food-legume crops for both humans and livestock in tropical and subtropical regions, and globally they are the fourth largest source of edible oil (Mondal et al., 2020). China leads in the production of peanuts, 35.93% of world production, followed by India (13.80%) and Nigeria (9.13%) in 2019 (FAOSTAT, 2019). According to Statista report, Henan is the leading producer of peanut in China with production of 5.767 million metric tons in 2019 (Statista.com, 2020) followed by Shandong and Guangdong regions.

Balanced fertilization is one of the most critical groundnut production management strategies to improve crop yield and quality. Assessing pod yield and plant nutrient demand can provide theoretical guidance for fertilization management of high-yielding peanut. Being a legume, peanut gets most of its N from nitrogen-fixing bacteria (Bradyrhizobium) colonizing the plant’s roots, however, peanut does require a small rate of N as a starter fertilizer. Adequate rates of P, K and S application are essential to obtain considerable yields and quality. Sulfur is now recognized as the fourth major plant nutrient after N, P and K, and an integral part of balanced fertilization and nutrition for oilseed crops including groundnut. Calcium is another critical nutrient in groundnut production (Baughman and Dotray, 2015). Various research results indicated that peanut responds to P (Dzomeku et al., 2019), K (Pradyut et al., 2006; Reddy et al., 2011; Sharma et al., 2011; Lobo et al., 2012), Ca (Xiao-long et al., 2018), S (Ariraman and Kalaichelvi, 2020) and B (Singh et al., 2009) especially when these nutrients are deficient in the soil where peanut is grown and where there is sufficient supply of other nutrients.

Polyhalite is a sedimentary marine evaporate fertilizer that supplies multiple essential primary, secondary and micronutrients. Mined in the UK by ICL Fertilizers, and marketed under the trademark Polysulphate^®, polyhalite consists of a hydrated sulfate of K, Ca and Mg with the formula: K₂Ca₂Mg(SO₄)₄·2(H₂O), which contains 48% S. Sofipoly on the other hand is a granulated fertilizer produced from polyhalite and SOP (sulphate of potash) and consists of 30% K₂O, 15.7% S, 5.8% CaO, 10.2% MgO and 0.3% B. Both fertilizers have attracted strong interest in China as they can provide the nutrients needed to help farmers increase yields and become more productive.

Currently, the practice of blanket fertilization in peanut production is widespread, especially in rural areas of China. This continuous and higher dose use of nitrogen and phosphate fertilizers, and lower use of other essential nutrients like potassium would result in unbalanced nutrient input and low fertilizer efficiency (Swarup, 1998; Mahajan and Gupta, 2009). In peanut, N, P and K compound fertilizers have been widely used in production and have greatly boosted peanut yield in the past. However, recently the yield of peanuts has not increased much, even with an increased use of N, P and K compound fertilizers indicating that other essential nutrients are becoming limiting. Use of fertilizers containing Ca, Mg and S is rare in the study area.

Previous studies have shown that NPK combined with calcium and magnesium sulfate fertilizers significantly increased the yield of rape (Tian et al., 2019), rice (Zhao et al., 2014), pakchoi, tea, and watermelon (Lin et al., 2005). In Jinzhou, Fujian and other places, experiments applying calcium, magnesium and sulfur containing fertilizers to peanut have shown that peanut yield has increased significantly (Huang et al., 2014). However, there is limited information on the effect of NPK combined with Ca, Mg and S nutrients on yield, nutrient content and partitioning of peanut in Henan province of China. The objective of this experiment is therefore to study the effects of combined application of conventional NPK fertilizer with polyhalite and Sofipoly fertilizers on peanut yield, nutrient content and partitioning, and quality in Henan province of China.

Materials and methods

The field experiment was conducted at the experimental farm of Henan University of Science and Technology (33°35'-35°05'N, 111°8'-112°59'E), Henan, China in 2019. Combinations of conventional NPK and polyhalite fertilizer treatments, and conventional NPK fertilizer as the control treatment, were tested. Details of the treatment combinations used in the experiment are presented in Table 1.

The test site is in a temperate zone, with a semi-humid and semi-arid continental monsoon climate. The site has a mean annual temperature between 12.1-14.6°C, mean annual rainfall of 600 mm, annual average evaporation 2,113.7 mm, and annual average radiation 491.5 kJ cm^–2. The annual sunshine hours are 2,300-2,600 hours, and the frost-free period is 215-219 days. Monthly mean temperature and precipitation from 2010 to 2020 are displayed in Table 2. The soil of the test site is characterized as yellow fluvo-aquic, the main soil type in the North China Plain which produces almost 60-80% of China’s wheat and 35-40% of China’s maize every year (Kong et al., 2014). Preplant soil samples were collected at 0-20 cm depth to determine selected physicochemical properties. The soil samples were air dried, ground to pass 2 mm, and analyzed for soil alkaline N using alkaline diffusion method (Mulvaney and Khan, 2001), available P using NaHCO₃ method (Olsen et al., 1954), available (exchangeable) Ca, Mg and Fe using EDTA extraction-ICP method (Barrows and Simpson, 1962), available S using calcium chloride solution extraction-ICP method (Houba et al., 2000) and available potassium using 1N ammonium acetate extraction-ICP method (Johnson and Goulding, 1990; Normandin et al., 1998). The physicochemical properties of the experiment soil are displayed in Table 3.

Peanut variety Huayu 16 was used as the test material for the experiment. The experiment plot size was 3.5 × 5 m. Seeds were planted at a row spacing of 35 cm with 20 cm between planting holes and two seeds were planted in each hole. Ridge planting was adopted with bottom and top ridge width of 70 cm and 45 cm, respectively. The experiment had 8 treatments arranged in a randomized complete block design with three replications. Fertilizers for each treatment were broadcast applied before ploughing. The peanut planting and harvesting dates were 16 June 2019 and 22 October 2019, respectively.

Plant samples were collected at four different growth stages (32, 50, 67 and 111 DAE) for leaves and stems, and at 67 and 111 DAE for nuts, to determine plant fresh weight, dry weight and concentration of N, P, K, Ca, Mg and S following standard procedures for each. Four randomly selected plants from two holes were sampled from each plot at each stage. The concentration of phosphorus, potassium, calcium, magnesium, and sulfur in the plants were determined by inductively coupled plasma (ICP) after digestion in a mixture of concentrated HNO₃ and H₂O₂ in a microwave oven. Nitrogen was determined by Kjeldahl after digestion in a mixture of concentrated H₂SO₄ and H₂O₂.

The effects of different combinations of the applied NPK and polyhalite fertilizers on the biomass accumulation and partitioning were statistically analyzed using ANOVA.

Results

The experiment soil was loamy in texture and alkaline in reaction with very high organic matter content, low available P and low alkali hydrolyzable nitrogen. The bulk density was low, indicating that it is not compacted and is suitable for plant growth (Table 3).

Combined application of NPK fertilizer with polyhalite affected the fresh and dry weight of peanut plant parts at different growth stages. The fresh weight of peanut showed an increasing trend up to 67 DAE and decreased afterwards in most of the treatments except the control where the fresh weight increased with increasing age (111 DAE). Treatment T2 gave the highest fresh weight at all stages of growth compared to other treatments, followed by T3, while the lowest was T7 (Fig. 1A). Peanuts’ fresh biomass yield ranged from 0.54 to 0.76 kg plant^–1 at 111 DAE. The highest yield was obtained from T3 and the lowest from T5. Combined application of NPK with polyhalite gave the highest yield, followed by NPK only. The effect of polyhalite reduced as the amount of NPK decreased.

Similarly, leaf dry weight showed an increasing trend until 67 DAE and decreased at later stages in all treatments. On the contrary, stem dry weight and nut dry weight increased as the plant gets to maturity (111 DAE). The highest stem and nut dry weight were obtained from T2, and the lowest was from T7 (Fig. 1B, 1C, 1D). Highest leaf dry weight was obtained at 67 DAE from T2 and the lowest from the control at the same stage. Highest stem dry weight was obtained at 111 DAE in most treatments, except that of T2, T4 and T5 treatments where higher stem dry weight was obtained at 67 DAE. T3 gave the highest stem dry weight followed by the control at 111 DAE. Lowest stem dry weight was obtained from T5 followed by T7 where the lowest amount of NPK (70%) was applied with the same amount of polyhalite, indicating that optimum application of NPK is required to benefit from the additional nutrients supplied by polyhalite.

Discussion

Appropriate crop nutrition management through balanced fertilization is crucial for sustainably achieving higher yield and quality of produce. Like other crops, peanut also requires a sufficient supply of essential nutrients other than N and P. In this experiment, application of polyhalite fertilizers in addition to the conventional NPK practice resulted in better yield and nutrient content in different parts of the peanut crop, and at different growth stages. This could be due to the effect of additional nutrients such as S, or Ca, and their interaction with other nutrients.

In line with this, previous studies indicated that exogenous calcium application had significant positive effects on absorption and accumulation of nitrogen, phosphorous, calcium and magnesium in different organs of peanut under salt stress (Xiao-long et al., 2018; Yadav et al., 2015). In their 2-year study, Abdel-Motagally et al. (2016) showed that sulfur application had a significant influence on yield and quality parameters in both seasons. Similarly, Patel and Zinzala (2018) have also reported that application of S and B improved yield and nutrient contents of peanut. Kabir et al. (2013) also reported that P, Ca and B application significantly increased plant height, number of branches plant^–1, and total dry weight of peanut.

In summary, basic NPK containing fertilizers are commonly used in China, however the result from this experiment is an indication that application of additional nutrients is required to improve crop performance. Besides yield and quality of peanut, understanding the effect of these fertilizers on soil properties after harvest and their role in nodulation needs further investigation. Dry matter yield and nutrient concentrations in different plant parts were affected differently. Application of NPK with 375 kg ha^–1 polyhalite gave higher stem dry weight, which could be due to the addition of 72 kg ha^–1 S and 43 kg ha^–1 of K. On the other hand, application of 70% NPK with 375 kg ha^–1 polyhalite gave the lowest dry matter yield indicating that optimum application of NPK is required to benefit from the applied nutrients from polyhalite. Potash and S responses will be visible when there are sufficient amounts of N and P, which are the most limiting elements. The results indicated that application of K and S contributed to improvements in yield and nutrient content. But adding higher contents of these two nutrients (beyond 161 kg ha^–1 K₂O and 72 kg ha^–1 S) do not continue improving yield and nutrient content in peanut. It is therefore recommended that determining the optimum rates of K and S under balanced application of other nutrients is required. Further multi-location and multi-year experiments are required to make optimum rate recommendations for S and K. Economic analysis of the fertilizer combinations is also required.

Acknowledgement

This study was supported by the International Potash Institute (IPI), Zug, Switzerland.

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