Balanced Fertilization for Sustainable Yield and Quality of Peanut (Arachis hypogaea L.) in Sandy Soil of Central Vietnam

Peanut (Arachis hypogaea L.) is a short-term crop with high economic and commercial value, grows best on sandy soils and has capability to improve soil health. In Vietnam, according to Vietnam’s soil classification, among 8 main soil groups in Binh Dinh province (South Central Coast Vietnam- SCV), sandy soil covers an area of 13,283 ha and accounts for 9.7% of agricultural production land area (Hoang et al., 2015).
       
The sandy soil in coastal provinces in general and Binh Dinh province in particular is basically sand, with light texture, high fine sand content, with about 2.5 to 12.5%, field moisture capacity, low in total nutrient content, poor in organic matter, hence have low ability to retain water and nutrients (Hoang et al., 2016).
       
The area of   peanuts in Binh Dinh in recent years has continuously increased from 8,713 ha (in 2015) to 10,040 ha (in 2018) (Hoang et al., 2022). However, peanut cultivation on sandy soil in Binh Dinh province still stagnant due to imbalanced fertilizer use, limited irrigation availability and low soil moisture holding capacity, appropriate varieties for cultivation and low planting distance and density.
              
Although researches on fertilizer for peanuts cultivation have been increased (Meena et al., 2018; Hoang et al., 2015), however, studies on nutrients recommendations especially fertilizers including K and S for peanuts on sandy soil are still limited. Previously, the effects of nutritional deficiencies on peanut yield on sandy soils in South Central Coast (SCC) region showed that without N application, the yield of peanuts decreased from 15.5 to 21.4%, while without K application, it decreased from 15.5 to 21.4% and without S application, yields decreased from 12.71 to 23.35% on sandy soils in Binh Dinh province (Hoang et al., 2016). Therefore, the present study was carried out to evaluate the effect of fertilizer combinations involving N, K and S in comparison with farmer’s practice to improve productivity and quality, as well as soil properties in peanut production on sandy soil in Binh Dinh province, SCC, Vietnam.

The field trial sites were in communes of Cat Hiep (14°03'05"N and 109°99'52"E) and Cat Hanh (14°05'46"N and 109°00'16"E), Binh Dinh province, SCC region. The soils are classified as Haplic Arenosols with deep sands, containing >95%. The region has a tropical savannah climate with long dry seasons (January to August) and high evaporation rates (about 100 mm month^-1), monsoonal rainfall (average of 1,900 mm), which is concentrated over a short spell (September to December) and mean temperatures between 27 and 35°C. The soil physico-chemical properties before and after experiment at two locations are presented in Table 4.
       
Peanut (Arachis hypogea L.) cv. Ly, a cash crop usually grown on sandy soils in SCC, was sown with two treatments including two different fertilizer schedule (T₁) control (Farmers’ practice): 24 kg N (urea) + 74 kg P₂O₅ (Thermophosphate) + 84 kg K₂O (KCl) + 100 kg NPK (16-16-8-13S) ha^-1 and (T₂) 40 kg N (urea) + 90 kg P₂O₅ (Thermophosphate) + 90 kg K₂O (K₂SO₄) based on 8 tons of cattle manure + 500 kg lime ha^-1, in complete randomized block design with three replications during spring season of December 2020 to April 2021 in Cat Hiep and Cat Hanh communes locations, Phu Cat district, Binh Dinh province. A local variety of peanut (cv. Ly) was sown on 26^th December 2020 in Cat Hanh commune and 28^th December 2020 in Cat Hiep commune.
       
Each experimental unit had an area of 50 m² with total area of 300 m2 of each trial. Peanut seeds were sown at a distance of 0.3 m between rows and 0.1 m between plants to get a total density of about 3,30,000 plants ha^-1. Nitrogen (N), phosphorus (P), potassium (K) and sulfur (S) were used as urea (46% N), thermophosphate (16% P₂O₅), potassium cloride (60% K₂O), potassium sulfate (50% K₂O) and NPK 16-16-8-13S (13% S). Lime (CaCO₃-56% CaO) was applied two weeks prior to sowing as a broadcast and incorporated to a soil depth of 20 cm. The required amount of cattle manure (1.12-1.21% N, 0.92-1.14% P₂O₅, 1.41-1.62% K₂O, 0.06-0.08% S), phosphorus and sulphur were applied at sowing by row application. The N and K fertilizers were also dressed following row applications at two stages of plant growth i.e., 12 days after sowing, one third of total at full expansion of the third leaf and and 35 days after sowing, the remaining two third just prior to flowering.
       
Growth parameters including plant height, number of first branch, number of nodules (pod forming stage), leaf area and biomas were measured from 10 plants plot^-1 at harvesting stage. The 98 days after sowing at harvesting stage, pod yield  at moisture <14% and other yield attributes  viz.,  shoot dry matter, pods number and shell weight were assessed from a quadrat measuring 4 m². Protein (Kjelhdal method) and lipid (Chromatographic method) contents were determined as peanut quality indicators (AOAC 2000).
       
Five soil samples were collected from the 0-20 cm layer from each experimental plot and combined to make a composite soil sample before and after experiment. Immediately after collection, the samples were put in plastic bags and brought to the laboratory for treating with removing root debris and the soil samples were air-dried and ground to pass through a sieve of 2 mm size. Soil physio-chemical characteristics were determined by the methods of Page et al., (1996).
              
The collected data was subjected to statistical analysis with mean, SD (standard deviation) and Ttest by using SPSS version 21.

Effects on peanut growth and yield
 
The results showed that compared to control (farmers ‘practice) (T₁), growth of peanut in T₂ (40 kg N (urea) + 90 kg P₂O₅ (Thermophosphate) + 90 kg K₂O (K₂SO₄) + 8 tons of cattle manure + 500 kg lime ha^-1) was improved significantly at two study communes (Table 1). The application of fertilizers in combination increased peanut height by 4.1-4.5%, number of first branches plant^-1 by 5.0-9.7%, number of nodules at pod forming stage by 13.7-14.8% compared to control. The leaf area index and biomass of peanut with application of fertilizer combinations increased by 2.94-10.68% and 6.37-19.57%, respectively compared with control.
       

 
There was a significant difference among yield components of peanut (Table 2). The number of pods per plant was highest in treatment with combined application of fertilizers with an increase of 15.77-18.32% compared to control. Similarly, number of filled pods increased by 13.47-18.04%, weight of 100 pods by 0.66-0.93 g, weight of 100 seeds increased by 0.36-0.5 g compared with control. Peanut yield ranged from 4.35-4.48 t ha^-1 with application of fertilizers in combination in Cat Hiep and Cat Hanh communes, which increased by 18.17-19.59% and had a statistical difference compared with control.
       

 
Growth and yield of peanut increased with application of fertilizer combination including K and S. Hoang et al., (2022) reported that K is an important component in nutritional balance of peanuts in sandy soil. Therefore, K should be balanced at 20-30 kg N and 60 - 90 kg K₂O ha^-1. Hoang et al., (2021) indicated that an increase of peanut growth and yield with application of 30 kg S ha^-1 based on 40 kg N + 90 kg P₂O₅ + 60 kg K₂O + 500 kg lime + 8 t of cattle manure ha^-1 for varieties L14 and SVL1. Milica et al., (2013) showed that balanced fertilizer application had a positive effect in improving growth and development, yield and yield components of peanut. Addition of K at 90 kg K₂O ha^-1produced the highest peanut yield (Hoang et al., 2022). Depending on different types of soil and production conditions, supplementing with S helps peanut to affect growth, development, yield, and its components. Therefore, application of fertilizers combined with K and S fertilizers at appropriate rate gave the highest yield and yield components (Hoang et al., 2022). Hoang et al., (2019) also found that the actual pod yield in Cat Hiep and Cat Hanh communes varied from 3.10 to 3.91 t ha^-1 (2015) and 2.52 to 3.42 t ha^-1 (2016) with different rates of K application and pod yield increased from 2.67 to 3.86 t ha^-1 with increase in S rate. Fertilizer application in combination increased biomass, pod and seed yield of peanut. This increase in peanut is evident that potassium fertilization application at the rate of 110 kg of K₂O ha^-1 increased nutritional status, improving grain production of peanut crop in rotation with sugarcane (Patel et al., 2018).
 
Effects on peanut quality
 
When supplemented with fertilizers, especially K and S, protein and lipid contents in peanut increased from 24.44-24.61% and 52.56-52.65%, compared with farmer’s practice respectively. However, there was no significant difference among treatments (Table 3).
 

       
Sulfur (S) is important for peanut nutrition because, along with N, it forms proteins (Wang et al., 2013). As very mobile in soil, S reserves decline, where soils are cropped continuously without application of S-containing fertilizers. Several recent studies have demonstrated the significant contribution of S application to peanut yield and quality (Pratiwi et al., 2016; Solaimalai et al., 2020) evident the present study findings. Likely, non-significant effect of fertilizer in combination on protein and lipid contents is validated from) that fertilization treatments did not show any significant effects, neither on the lipid (49.7-52.4%) nor on protein (25.2-27.9%) content in the peanut seeds (Hoang et al., 2016).
 
Soil physico-chemical characteristics
 
The fertilizer treatments had significant effects on soil properties measured at the end of field experiment (Table 4). The soil acidity decreased with a little of soil pH from 4.76-4.84. Typical to humid tropical regions, soils tend to be very acidic, low in organic matter, and have low cation exchange capacity (CEC) (Hoang et al., 2016). Lime (CaO), which is a cheap base, is commonly used to reduce soil acidity. For peanut, recommended pH range is 5.8-6.2. If pH is less than 5.8, zinc (Zn) toxicity problems could occur (Balota 2014). In addition, urea application to acidic soils might further decrease soil pH (Tong and Xu, 2012) and weaken N₂-fixation by leguminous crops (Miller 2016). Appropriate crop nutrition management is crucial, particularly on sandy acidic soils in tropics. The sandy soil (97%) has very low CEC, and low pH (5.1), further reduces its ability to store nutrients. The substantial CaO supplement (500 kg ha^-1) used in the present study gave rise to a significant though; there was uneven rise in soil pH (Table 4). The soil organic matter content increased a little in most treatments (0.83-0.85%). Soil N concentration increased, when fertilizer in combination was applied. Available soil P increased from 7.43 to 7.48 mg 100 g^-1 for all treatments. There was a slight increase in soil available K with fertilizer application in combination. However, sulfur content fluctuated within a narrow range from 0.025-0.028%. Peanut, a leguminous crop, does not require significant N inputs (Balota 2014). Lack of K, led to diminished levels of both soil N and K, which were gradually replenished with rising K application rates. These results indicate that K and S supply are essential for optimum peanut plant development which, in-turn, allows adequate N₂-fixation by the peanut roots, and hence soil enrichment with N as evident from increase in soil N contents of present study.
 

Application of fertilizer (40 kg of N (urea) + 90 kg of P₂O₅ (Thermalphosphate) + 90 kg of K₂O (K₂SO₄) + 500 kg lime ha^-1) in a combination of 8 t ha^-1 of cattle manure for peanut in sandy soil improved biomass by 6.37-19.57%, yield by 18.17%, including quality parameters viz., lipid and protein content and soil properties compared to farmers practice. In crux, for better peanut production of high quality in sandy soil, it is recommended to apply the fertilizer in combination with K and S.

This work was partially supported by Hue University under the Core Research Program, Grant No. NCM.DHH.2020.07.

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