Effect of NPK fertilizer and soil amendments of soybean productivity in saline soil

Salinity on agricultural land due to global warming occurs almost all over the world. Salinity stress was harmful to cultivated plants, including soybeans. Saline soils require the management of nutrients and water to reduce salt from the soil so that plants can grow optimally. This study aims to obtain effective doses of NPK fertilizers and soil amendments for soybean cultivation in saline soils. The research was conducted during the 2019 rainy and dry seasons in Lamongan and Tuban Regencies, East Java Province, Indonesia. The electrical conductivity (EC) of soil during the growing season was 5-12 dSm-1, with irrigation water was 6-7 dSm-1. The treatment consisted of NPK fertilizers, ameliorants: gypsum, manure, and straw mulch, which were arranged in a randomized block design and replicated 15 times. The results showed that the Anjasmoro variety of soybean productivity on saline in the Lamongan Regency during the rainy season was higher (90%) than in the Tuban Regency in the dry season. Application of NPK Fertilizer (46 kg N + 108 kg P2O5+ 60 kg K2O ha-1 + or 400 NPKS kg ha-1 with ameliorants (gypsum 1.5 t ha-1; manure 2.5-5.0 t ha-1 and straw mulch 3.5 t ha-1) have the potential to increase soybean yield up to 2 t ha-1 on saline soil.


Introduction
Increased salinity on agricultural land was a serious threat to the sustainability of crop production.Salinity stress was found to reduce plant growth, physiological function, and yield [10].Most cultivated plants were very sensitive to salinity, including soybeans [9].It was estimated that the salinization of agricultural land will continue to expand, especially in arid and semi-arid areas.Approximately 500 million hectares of agricultural land have decreased productivity due to salinity problems [2].It was estimated that the saline area in Indonesia will also continue to increase because Indonesia is the fourth longest coastal country in the world (95,181 km).Increased salinity in Indonesia was likely due to global climate change and rising sea levels [19], seawater intrusion [13;11], waste pollution [8; 32], various factors such as excess irrigation and poor drainage, groundwater salinity, sea level rise, and intrusion, irregular rainfall contributes to the process of soil salinization [12].
Saline soils have a high salt content in the soil solution.Most of the cations in saline soils were Na + , and some other cations in lower concentrations, such as Ca 2+ , Mg 2+ , and K + .Meanwhile, soil anions include Cl -, SO4 2-, HCO3 -, and CO3 2- [29].High levels of dissolved salts cause osmotic stress, nutritional imbalances, and ion poisoning in sensitive plants.The high salt content in the soil causes deterioration of soil physics and chemistry, soil microbial, and plant growth [36].Increasing soil salinity negatively affects the stability of soil structure, soil-specific gravity, and soil permeability [35].Plant tissues that grow in saline soil conditions are generally hampered due to the accumulation of Na + and Cl -ions or inhibition of absorption of nutrients such as Ca 2+ , K + , N, and P [22].Thus, fertilization is necessary to increase plant nutrient uptake.
Soybean was a cultivated plant that was sensitive to salinity stress.The salinity threshold for soybean, according to [5], was at 5.0 dSm -1 .At a soil salinity of 4.0 dSm -1 , the yield of soybean seeds decreased by 20%, and a decrease of 56% at a salinity level of 6.7 dSm -1 [21], and yield potential of 50% for soybeans was achieved at soil salinity levels ( soil ECs) of 7.5 dSm -1 [23].
Saline soil or salt affected soil for crop cultivation requires nutrient management, including fertilization and amelioration/soil amendments to improve soil function both fertility and physical properties.The effect of adding ameliorant was the exchange of Na + with Ca 2+ , which allows sodium leaching to be exchanged.Gypsum was the most commonly used inorganic ameliorant as a supplier of Ca 2+ ions and its effectiveness in saline soil amelioration has been extensively studied [6; 16; 15].Elemental sulfur and sulfuric acid were ameliorants commonly used in saline soils that can dissolve soil calcium carbonate and increase Ca 2+ content [31].
The application of organic matter can improve the physical, chemical, and biological properties of the soil.The effectiveness of organic matter application to improve saline soils has been studied extensively [35].The addition of organic matter to saline soils can accelerate Na + leaching, reduce ESP and EC, increase air infiltration, and the ability to store air and stabilize soil aggregates [24; 34].Combining salinity-tolerant genotypes with the best soil management resulted in better effect as well as yield.Soybean yield of the Anjasmoro variety and K-13 line increased by 36% in saline soil with a salinity of 10 dSm -1 amended with 2.5 t manure ha -1 and 1.5 t gypsum ha -1 [33; 26].In previous studies on saline soil with soil conductivity 6-> 10 dSm -1 , soybean K-13 line productivity reached 1.5 t ha -1 in saline soil with fertilization at 46 kg N ha -1 and 108 kg P2O5 ha -1 [27].The appropriate P fertilizer dosage for both genotypes (Anjasmoro and K-13 line was 108 kg P2O5 ha -1 [25].In soybean under saline conditions, potassium sulfate showed a better positive effect on the antioxidant activities, polyphenol, flavonoid, carotenoid, and chlorophyll contents compared to those of potassium chloride [1].
Saline soil will be an alternative for developing soybeans in Indonesia due to the decreasing area of productive land and competition for land with other main food crop commodities such as rice and corn.The novelty of this research is that it combines the technological components of fertilization and amelioration of saline tolerant varieties of soybeans in saline soil to obtain recommendations for a technology package for cultivating soybeans in saline soil which is currently not available.Therefore, nutrient management technology was needed on saline soils in addition to using salinity-tolerant varieties to achieve high soybean productivity.Based on this, research needs to be carried out to obtain effective fertilizer NPK doses and amelioration in soybean cultivation in saline soil.

Place and Time of Study
The research was conducted in saline soil in East Java Province: Lohgung village, Brondong Sub District, Lamongan District, (6 o 5359.89801"S; 112 o 11 '15.3127"E; 26 m asl) and Gesikharjo Village, Palang Sub District, Tuban District (6 o 54'20.29482"S; 112 o 8 '18.35902"E, 31 m asl), covering an area of 4 ha belonging to cooperative farmers.The research location is 600 m from the sea with soil characteristics as shown in Table 1.In Lamongan, it was carried out in the 2019 rainy season (February-May 2019) and Tuban in the 2019 dry season (June-September 2019) with an average temperature of 27. 6 o C (Figure 1).The land used is a paddy field with a rice-bare cropping pattern.Both research site were considered considered as slightly-to-moderately saline based on the classification by USDA 1993 with EC ranged from 4 to 12 dSm -1 .In Lamongan EC the soil at the beginning of planting was 5.41 dSm -1 and in Tuban, it was 6.67 dSm -1 and EC at harvest time reaches 12 dSm based on the classification of USDA (1993), the soil is included in the category of moderately saline.

Procedure
The land was cleared of weeds or previous crop residues, with no tillage.Before planting, the seeds were mixed with an insecticide with the active ingredient fipronil or thiamethoxam to prevent peanut fly attacks.Seed planting was done manually by dibbling 2-3 seeds into the hole at a planting distance of 30 cm interrow and 15 cm interplant.Ameliorant 2.5 and 5 t manure and 1.5 t gypsum ha -1 were applied at planting time by spreading evenly.Fertilizer of N was carried out when the plants were 15 DAP and 30 DAP each as much as dose.P fertilizer and K fertilizer were applied at the same time as planting.Compound fertilizer (NPKS) 400 kg ha -1 equivalent (60 kg N + 60 kg P2O5+60 kg K2O +36 kg S ha -1 ) was applied at half the dose at planting and the rest at 30 DAP.Straw at a dose of 3.5 t ha -1 was used as mulch for the T1 treatment.Gypsum was spread evenly at planting for T2 treatment.Weeding was done twice (20 and 45 DAP) using herbicides.Irrigation using well water was carried out three times at the Tuban location.Pest control was carried out six times using chemical pesticides

Data Collection and Analysis
The variables of soil moisture content were gravimetric, electrical conductivity using an EC meter Hanna Instruments), and leaf chlorophyll index (CCI) at 15,35, 55, and 75 DAP.Observations were made on soil nutrient status at the beginning and after harvest (EC, pH, C-Organic, N, P, K, Na, Ca, Mg).Soil moisture content and EC were observed at a depth of 0-20 cm.Observations of CCI using SPAD-502 from Minolta Instruments were carried out on the second and third leaves from the shoots of ten plant samples.Growth scores on R1 and R5 with a scale: 1 = very good; 2 = good, and 3 = bad.Leaf K and Na levels were carried out at the age of 60 days after planting.Observation of yield and yield components of seeds (number of filled pods and empty pods, dry weight of seeds, and weight of 100 seeds.Observation of yield was based on seed yield on a 10 m 2 , while the yield component was based on a sample of 10 plants.Data were analysed using one way analysis of variance (ANOVA) according to randomized complete block design, and mean comparation using least significant difference (LSD) at 0.05 probability level.

Soil Properties
The soil in the study site of Lohgung Village, Brondong Sub District, Lamongan District, East Java Province (26 m asl) and at Gesikharjo Village, Palang Sub District, Tuban District, East Java Province (31 m asl) dominated by clay fraction.The soil reaction was slightly alkaline because the pH was more than 8.0 and had a low fertility level because the levels of N, P, and C-organic were relatively low, but had high levels of K, high SO4, and the microelements Cu, Zn and Fe were in sufficient status (Table 1).In Lamongan EC the soil at the beginning of planting was 5.41 dSm -1 and in Tuban, it was 6.67 dSm -

1
. Based on the classification of [20], the soil is included in the category of high salinity soil.Soil with high salinity has the potential to inhibit soybean plant growth due to high Na and pH levels and low N and P levels.The high soil pH results in most of the soil P being dissolved as sodium phosphate (NaH2PO4) [30;14.]

Soil Salinity vs Soil Moisture
The dynamics of soil salinity (EC) and soil moisture content at various ages of observation are shown in Figure 2. In Lamongan, soil salinity levels ranged from 5 -11 dSm -1 from 15 DAP until harvest, while soil moisture content was 12-29%, with a decreasing trend towards harvest.(Figure 2).Irrigation was not needed because the research was conducted during the rainy season (February -May 2019).Salinity levels at the Tuban location ranged from 7.5-12 dSm -1 from 15 DAP to harvest, with the soil moisture content of 16-44%.At the beginning of planting, it rained quite heavily, so the soil salinity at planting was very high, even in some plots of soil EC reaching above 20 dSm -1 .During the soybean growth period, irrigation was carried out three times using water from bore wells.Wells were the only source of irrigation in saline land and during the study, there was no rain; the main cause of the increase in soil salinity levels in saline land was drilled well water.The salinity of the well water increased from 5.79 to 7.27 dSm -1 on the third irrigation during pod filling.

Soil and Plant Nutrients
At Lamongan, the T1 treatment indicated that the soil chemical properties of N, P, K, Na, Ca, SO2, Fe, Zn, CEC, and soil Na saturation were lower than the T2 treatment (Table 2).Soil K/Na ratio was higher in T1 treatment, allowing plants to grow normally even though soil EC > 6 dSm -1 .In plant nutrient status, the leaf K/Na ratio in both T1 and T2 treatments was quite high, namely 308-334 (Table 3).The Leaf K/Na ratio, which was an indicator of plant tolerance to salinity stress shows that plants grow relatively well with a fairly high K/Na balance.In contrast, in Tuban, the T1 treatment showed lower plant content of N, P, K/Na, Ca, SO2, and Fe than the T2 treatment.However, in both treatments, the Na saturation was relatively high up to 20.8% (Table 2).The leaf K/Na ratio in the T1 treatment was higher than T2 (4.78-17.4),which was much smaller than at the Lamongan location (Table 3).Increasing K uptake is one of the mechanisms of crop tolerance to salt stress because K has competitive properties against Na in maintaining water status in the crop [3].

Plant Growth
Fertilization treatment and soil amendments between T1 and T2 in Lamongan did not significantly affect growth variables such as chlorophyll content index, growth score, and plant height (Table 4 and Table 6).Plants grow normally even though the soil salinity reaches 7 dSm -1 .Visually, the plants did not appear to be experiencing salinity stress, so the plant growth score had a value of about 1.0 both in the R1 phase and during the R5 phase.This can also be seen in the plants that grow well, with a plant height of 67-70 cm at harvest.In the treatment plant biomass, T1 was higher than T2.The numbers in the same column with the same letters or without letters in the same treatment group showed no significant difference according to the T-test.
At the Tuban location, soil amendment treatment and fertilization affected the chlorophyll content index at 35 and 55 days after planting (Table 5).The T1 treatment had a better effect on CCI Treatment 2. The chlorophyll content index reached a peak at 55 DAP, with Treatment 1.At 75 DAP, the leaves experienced a drastic decrease; this was probably due to the complex influence of salinity stress, relatively high air temperature, and indications of deficiency in P. A study by [17] showed that a reduction in chlorophyll fluorescence due to salinity stress was related to the damage of chlorophyll under saline conditions.Plant growth was also inhibited in both T1 and T2 treatments (Table 7).Plant growth in the Lamongan location was better than in the Tuban location; this is reflected in the inhibition of plant growth in Tuban.Plants grow shorter with lower plant biomass.In another study, the application of P fertilizer on black paper (Paper nigrum) reduces salt stress through increasing assimilation of N, P, K, Mg, Ca, Fe, Zn, Mn, and Cu [7].

Yield and Yield Attributes
The application of NPK fertilizer and ameliorant only affected the dry weight of the stover at harvest, the number of branches, the number of filled pods, and the dry weight of the pods (Table 8).Treatment 2 using 60 kg N + 60 kg P2O5+60 kg K2O +36 kg S ha -1 +1.5 t gypsum + 2.5 t manure ha -1 gave an increase of about 11-17% in the number of branches, number of filled pods, and dry weight of pods.In general, the two treatments have the same effect because the productivity achieved does not differ between treatment 1 and treatment 2. Soybean productivity in saline Lamongan in the rainy season reached 2.78-2.89t ha -1 in the two treatments used.This is because soil salinity is not a limiting factor for crop production.
In Tuban, the application of NPK fertilizer and ameliorant did not significantly affect the yield and yield components of seeds (Table 9).At harvest time, the plant has 3 branches, with 33-34 filled pods; the number of empty pods is 1.45 on average, the weight of the filled pods is 13.9-15.3g plant -1 , the seed weight is 7.72 g on average, the weight of 100 seeds is 10.78-14.14 and productivity per hectare ranges from 1.45-1.53t.This productivity is quite good, considering the soil and agroecological conditions with high environmental stresses, including salinity stress, drought, and high daytime air temperature.As in other studies, soybean seed yields increased linearly with potassium fertilization in saline soils [18].Yields at the Lamongan location were 91% higher than at the Tuban location.In Tuban, planting was carried out during the dry season, resulting in more severe drought and salinity stress.In contrast to Lamongan, planting was carried out in the rainy season without environmental stress during its life phase.The research results showed that the Anjasmoro variety was indicated to be salinity tolerant; under stress conditions until the soil EC reaches 10-12 dSm -1 , it can produce seeds up to 1.4 t ha-1 with fertilization and ameliorant.This was similar to previous research on soybean cultivation in saline land [25; 26; 27; 33].
Currently, the combination of salinity tolerant soybean genotypes and nutrient management is a good strategy to increase soybean yields on saline soils.As the results of previous studies on saline-alkaline soils [37;4,] gypsum application is a viable strategy for reclaiming sodic soils, and combined organic amendments and mineral fertilizer application were better in improving the soil structural stability, P availability and plant growth in the saline-alkaline area.As reported by [39] Application of gypsum increased soybean yield, Ca 2+ , and K + concentrations in leaves and grain protein.Meanwhile, other types of ameliorant such as water hyacinth compost and rice husk biochar have a positive effect in mitigating the negative impact of salinity on soybean plants.[40].

Conclusions
The rainy season provides a good environment for the growth of soybean plants on saline soils in the Lamongan Regency.During the dry season, soybeans in the saline soils of Tuban district suffer from salt stress and drought.Application of NPK Fertilizer + ameliorants and salt tolerant soybean cultivar such as Anjasmoro can be recommended for soybean cultivation on saline soils with EC 6-12 dSm -1 .The two fertilization treatments were T1: 46 kg N + 108 kg P2O5 + 60 kg K2O ha -1 + 5 t manure + 3.5 t straw mulch ha-1 and (T2) NPKS fertilizer 400 kg ha -1 equivalent to (60 kg N + 60 kg P2O5+60 kg K2O +36 kg S ha -1 ) + 1.5 t gypsum + 2.5 t manure ha-1 can be applied to soybean cultivation in saline soils both in dry and rainy seasons.

Figure 1 .
Figure 1.Rainfall and air temperature at Tuban District.2019

Figure 2 .
Figure 2. Soil EC and soil moisture content at Lamongan district (A) and (B) at Tuban district during soybean growth.2019.

Table 1 .
Chemical properties of top 0-20 cm composite soil sample at pre-planting.Tuban and Lamongan District

Table 2 .
Chemical properties of top 0-20 at 60 DAP on two treatments of fertilizers and soil amendments of soybean in Lamongan and Tuban districts

Table 3 .
Nutrient content of soybean leaf R5 phase on two treatments of fertilizers and soil amendments in saline soil, Tuban and Lamongan districts

Table 4 .
Effect of fertilizers and soil amendments on soybean chlorophyll content index and growth score in saline soil at.

Table 5 .
Effect of fertilizers and soil amendments on soybean chlorophyll content index and growth score in saline soil at.

Table 6 .
Effect of fertilizers and soil amendments on soybean height and biomass in saline soil.at

Table 7 .
Effect of fertilizers and soil amendments on soybean height and biomass in saline soil.atThe numbers in the same column with the same letters or without letters in the same treatment group showed no significant difference according to the T-test

Table 8 .
Soybean yield and yield attributes on two treatments of fertilizers and soil amendments in saline soil.Lamongan district, Rainy season 2019

Table 9 .
Soybean yield and yield attributes on two treatment of fertilizers and soil amendments in saline soil.Tuban district, Dry season 2019