Effects of Water-Soluble Fertilizer on Yield and Quality of Asparagus in Greenhouse under Chemical Fertilizer Reduction

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1. Cixi Agricultural Technology Extension Center, Cixi 315300, China; 2. Cixi Agricultural Monitoring Center, Cixi 315300, China

Abstract In order to understand the effects of water-soluble fertilizer on the yield and quality of asparagus in greenhouse, taking conventional fertilization as a control, in the case of a decrease in total nutrient of chemical fertilizer, the application effect of humic acid-contained water-soluble fertilizer in asparagus was studied by experiment. The results show that, under the condition that the conventional fertilizer was reduced by 30% and 50%, the application of humic acid-contained water-soluble fertilizer to asparagus in greenhouse can improve the shoot length, single shoot weight, shoot diameter and shoot growth (degree of scatter) of asparagus, improve effectively the quality of asparagus (e.g. increasing the content of vitamin C and decreasing the nitrate content in asparagus shoots), and increase the yield of asparagus shoots (by 2 583 and 4 218 kg/ha compared with the conventional fertilization, with growth rates of 10.3% and 16.8%, respectively).

Key words Water soluble fertilizer, Fertilizer reduction, Asparagus

1 Introduction

Humic acid has the five major functions of improving soil, improving fertilizer efficiency, stimulating growth, promoting stress resistance and improving quality. It can enhance soil water retention capacity and improve crop drought and cold resistance. Humic acid-contained liquid fertilizer can increase the commodity rate of tomato and promote the plant growth and chlorophyll synthesis of cucumber, making the yield of cucumber and tomato increased by 7.2% and 6.3%-38.0%, respectively[1]. Humic acid can stimulate the growth and development, enhance the resistance, increase the yield, and improve the quality of vegetables[2]. It indicates that humic acid plays an important role in promoting vegetable growth and improving vegetable quality. Therefore, it is necessary to vigorously promote the application of humic acid-contained fertilizer on vegetables.

Taking conventional fertilization as a control, high-nitrogen and high-potassium humic acid-contained water-soluble fertilizer was applied through water and fertilizer integration technology during the different growth stages of asparagus in greenhouse, and the conventional fertilization amount was reduced by 30% and 50% simultaneously to study the effects of fertilizer reduction on the yield and quality of asparagus, in order to provide a reference for the large-scale promotion and application of water-soluble fertilizer in greenhouse asparagus.

2 Materials and methods

2.1 Test materialsThe used fertilizers included drip irrigation-specific Wotu water-soluble fertilizer (humic acid≥30 g/L, N+P2O5+K2O≥200 g/L, total N≥100 g/L, P2O5≥50 g/L, K2O≥50 g/L), foliar spray Miaohuan water-soluble fertilizer (free amino acids≥100 g/L, Ca+Mg≥30 g/L), Guole water-soluble fertilizer (free amino acids≥100 g/L, Ca+Mg≥30 g/L, K2O≥40 g/L). They were developed by the Institute of Agricultural Chemistry of Zhejiang University, and produced by Zhejiang Aojie Biotechnology Co., Ltd.

The test crop was 6-year-old Grande, an asparagus variety, planted in 2010.

The test was carried out at Xiaolin Lixin Vegetable Plantation. The soil test was carried out before the test. The soil to be tested was calcareous alluvial soil with pH of 6.96, organic matter of 8.12 g/kg, total nitrogen of 1.04 g/kg, hydrolyzable nitrogen of 72 mg/kg, available phosphorus of 35.30 mg/kg and available potassium of 450 mg/kg. The fertility of the soil was medium.

2.2 Test design and methodsThe test was conducted from July 2016 to December 2017. In the wide field trial, each greenhouse had an area of 370 m2, without replicates. In the asparagus harvest period, the output was calculated and the economic performance was examined. Except the application of fertilizers in strict accordance with the test design, the other agronomic measures were exactly the same. They were all carried out under the conditions of uniform irrigation and pest control. The contents of vitamin C, fructose and sucrose, and nitrate in the asparagus shoots were determined according to GB 5009.86-2016, GB/T 22221-2008 and NY/T 1279-2007, respectively. Soil pH and organic matter, total nitrogen, hydrolyzable nitrogen, available phosphorus, available potassium and salts contents were measured and determined according to NY/T 1121.2-2006, NY/T 1121.6-2006, NY/T53-1987, LY/T 1229-1999, LY/T1233-1999, NY/T 889-2004 and LY/T1251-1999, respectively.

A total of three treatments were designed: Treatment 1, conventional fertilization (control); Treatment 2, 70% conventional fertilization+humid acid-contained water-soluble fertilizer; Treatment 3, 50% conventional fertilization+humid acid-contained water-soluble fertilizer.

In treatment 1, rabbit feces (22 500 kg/ha) and compound fertilizer (N∶P2O5∶K2O=14∶16∶15) were applied at the end of July and December of 2016 as a base fertilizer. The compound fertilizer was applied at a dose of 1 500 kg/ha for two times. During the harvesting of the asparagus from March to June and August to September of 2017, the compound fertilizer was applied once a month for four times, with a dose of 750 kg/ha, so that the topdressing amount was 3 000 kg/ha. In conventional fertilization, a total of 6 000 kg/ha of compound fertilizer was applied throughout the year.

In treatment 2, the application of organic fertilizer was the same as the control. The cumulative application amount of conventional compound fertilizer throughout the year was 4 200 kg/ha. Wotu humic acid-contained water-soluble fertilizer and foliar fertilizers were applied as topdressing. During the growth period of asparagus, a total of 12 times of application of water-soluble fertilizer were carried out (Table 1).

In treatment 3, the application of organic fertilizer was the same as the control. The cumulative application amount of conventional compound fertilizer throughout the year was 3 000 kg/ha. Wotu humic acid-contained water-soluble fertilizer and foliar fertilizer were applied as topdressing. During the growth period of asparagus, a total of 12 times of application of water-soluble fertilizer were carried out (Table 1).

Table 1 Application of water-soluble fertilizer and foliar fertilizers in treatments 2 and 3

ApplicationperiodHumidacid-containedwater-solublefertilizerIrrigationmodeApplicationamount∥haFoliarfertilizerSeedlingnurseryDripirrigation75kg/time,onetimeevery15d,totaltwotimesMiaohuan400×diluent,onetimeevery15d,totaltwotimesHarvestDripirrigation75kg/time,onetimeevery15d,totaleighttimesGuole,Miaohuan300×diluents,twotimesinAprilandSeptemberalternativelyPost-harvestDripirrigation75kg/time,onetimeevery15d,totaltwotimesMiaohuan300×diluent,onetime

3 Results and analysis

3.1 Effects of different treatments on the commodity properties of asparagus shootsAs shown in Table 2, when humid acid-contained water soluble fertilizer and foliar fertilizer were applied on the basis of 30% and 50% reduction of conventional fertilization, the commodity properties of asparagus shoots were obviously improved. Compared with those in treatment 1, the shoot lengths in treatments 2 and 3 increased by 1.7 and 2.4 cm, respectively; the single shoot weights increased by 4 cm and 9 g, respectively; the percentages of shoots with diameter of grade I (>1.2 cm) increased by 11.9 (30.5%) and 14.3 (32.9%) percentage points, respectively; the percentages of shoots with diameter of grade II (>1.0 cm) increased by 0.6 (23.2%) and 2.7 (25.3%) percentage points, respectively; the percentages of shoots with diameter of grade III (>0.8 cm) increased by 10.8 (84.0%) and 13.2 (86.4%) percentage points, respectively; and the percentages of shoots with growth (degree of scatter) above grade III increased by 12 and 16 percentage points, respectively.

Table 2 Effects of different treatments on commodity properties of asparagus shoots

TreatmentLengthcmSingleshootweight∥gPercentageofshootsofdifferentgradeofdiameter∥%IIIIIIIVVGrowth(degreeofscatter)∥%IIIIIIIV1(CK)39.735.618.622.632.016.010.816202440241.439.630.523.230.39.26.818223228342.144.632.925.328.27.75.924223024

Note: Stem diameter: grade I, >1.2 cm; grade II, >1.0 cm; grade III, >0.8 cm; grade IV, >0.6 cm; grade V, ≤0.6 cm. Growth: grade I.

3.2 Effects of different treatments on the yield and economic benefits of asparagus shootsAs shown in Table 3, the average yields of the asparagus shoots in treatments 1, 2, and 3 were 25 089, 27 672 and 29 307 kg/ha, respectively. The average yields in treatments 2 and 3 were 10.3% and 16.8% higher than that in treatment 1, respectively, and when the average selling price was assigned as 7.0 yuan/kg, the average output values were increased by 18 081 and 29 526 yuan/ha, respectively. In treatment 1, 15 labor-hours per hectare were used for topdressing, according to 150 yuan/labor-hour, a total of 9 000 yuan/ha was cost for the four times of topdressing; a total of 0.3 labor-hour per hectare was used for water-fertilizer integration, and according to the labor price of 45 yuan/ha and the electricity cost of 15 yuan/ha, thus a total of 720 yuan was cost for the 12 times of application of water-soluble fertilizer; and the cost for the five times of application of foliar fertilizer was 2 700 yuan/ha (3.30-3.75 labor-hours per hectare). In total, the cost of water-fertilizer integration was reduced by 5 580 yuan/ha compared with that of conventional fertilization.

In conventional fertilization, the application level of compound fertilizer was 6 000 kg/ha, according to the price of 3.2 yuan/ha, the total cost of compound fertilizer was 1 280 yuan. The application level of water-soluble fertilizer was 75 kg/ha, according to the price of 14 000 yuan/t, and the total cost of water-soluble fertilizer was 12 600 yuan/ha. The prices of Miaohuan and Guole were both 30 yuan/100 mL. Each time, 60 mL of each of them was used. Thus, the total cost of the five times was 1 350 yuan/ha. In treatment 2, the application amount of compound fertilizer was reduced by 30%, only 4 200 kg/ha, and the cost was 13 440 yuan/ha. Compared with treatment 1, the total cost of compound fertilizer, water-soluble fertilizer and foliar fertilizer in treatment 2 was 27 390 yuan/ha, increased by 8 190 yuan/ha; and the labor cost was reduced by 5 580 yuan/ha; the output value was increased by 18 081 yuan/ha; and the net income was increased by 15 471 yuan/ha. In treatment 3, the application level of compound fertilizer was reduced by 50%, only 3 000 kg/ha, with a cost of 9 600 yuan/ha, and the cost of water-soluble fertilizer and foliar fertilizer was 13 950 yuan/ha, so the total cost of compound fertilizer, water-soluble fertilizer and foliar fertilizer was 23 550 yuan/ha, increased by 4 350 yuan/ha compared with treatment 1. Compared with treatment 1, the labor cost in treatment 3 was reduced by 5 580 yuan/ha, and the output value was increased by 29 526 yuan/ha, so the net income was increased by 30 756 yuan/ha.

Table 3 Effects of different treatments on yield and efficiency of asparagus per hectare

TreatmentAverageyield∥kgIncreaseinyield∥%Increaseinincome∥yuanFertilizercost∥yuanIncreaseinfertilizercost∥yuanCostsaved∥yuanIncreaseinnetincome∥yuan1(CK)250891920022767210.31808127390819055801610132930716.829526235504350558030756

Note: The price of asparagus shoots is assigned as 7.0 yuan/kg.

3.3 Effects of different treatments on the quality of asparagus shootsIn October 2017, samples were sent to the Testing Center of Ningbo Academy of Agricultural Sciences to test the contents of vitamin C, fructose, sucrose and nitrate in asparagus shoots. Table 4 shows that compared with treatment 1 of conventional fertilization, the contents of vitamin C in the asparagus shoots of treatments 2 and 3 were increased by 5.3 and 0.6 mg/kg, respectively; the contents of nitrate were decreased by 30 and 83 mg/kg, respectively; and the contents of fructose did not change significantly.

Table 4 Effects of different treatments on quality of asparagus

TreatmentVitaminCmg/kgFructose%Sucrose%Nitrate(NO-3)∥mg/kg1(CK)18.60.986Notdetected(<0.4)499223.90.834Notdetected(0.4)469319.20.968Notdetected(<0.4)416

3.4 Effects of different treatments on the fertility of soilThe soil in different treatments was sampled and analyzed, and the results are shown in Table 5. Compared with treatment 1, the contents of organic matter in the soil of treatments 2 and 3 increased by 1.56 (22.6%) and 3.49 (50.5%) g/kg, respectively; the total nitrogen contents were increased by 0.14 (16.9%) and 0.53 (63.9%) g/kg, respectively; the hydrolyzable nitrogen contents were increased by 33 (63.5%) and 26 (50.0%) mg/kg, respectively; the available phosphorus contents were increased by 1.76 (6.9%) and 11.26 (44.0%) mg/kg, respectively; the salt contents reduced by 0.01 and 0.24 mg/kg, respectively; and pH values declined by 0.04 and 0.33, respectively, nearly neutral. It indicates that the combination of chemical fertilizer reduction and humid acid-contained water-soluble fertilizer application can improve the fertility properties of the soil, greatly improving the quality of the soil in asparagus greenhouse.

Table 5 Properties of soil in asparagus greenhouse under different treatments

CodeofsoilsamplepHOrganicmatter∥g/kgTotalnitrogen∥g/kgHydrolyzablenitrogen∥mg/kgAvailablephosphorus∥mg/kgSalt∥g/kgBasicsoilsample6.968.121.047235.301.57Treatment17.696.910.835225.601.46Treatment27.658.470.978527.361.45Treatment37.3610.401.367836.861.22

4 Conclusions and discussion

4.1 Effects of water-soluble fertilizer containing humid acid and foliar fertilizer on the quality of asparagusThe combined application of humid acid-contained water-soluble fertilizer and foliar fertilizer can increase the shoot length, single shoot weight, shoot diameter and shoot growth (degree of scatter), improve the quality, increase the content of vitamin C and reduce the content of nitrate in asparagus.

4.2 Effects of water-soluble fertilizer containing humid acid and foliar fertilizer on the yield of asparagusOn the basis of 30% and 50% reduction of compound fertilizer, application of humic acid-contained water-soluble fertilizer can increase the yield of shoots, 2 583 and 4 218 kg/ha, respectively compared with conventional fertilization, with growth rates of 10.3% and 16.8%.

4.3 Effects of water-soluble fertilizer containing humid acid and foliar fertilizer on the economic benefits of asparagusThe application of humid acid-contained water-soluble fertilizer to greenhouse asparagus can save labor and increase efficiency. Even when the application amount of compound fertilizer is reduced by 30% and 50%, the net income is still increased by 15 471 and 30 756 yuan/ha.

4.4 Effects of water-soluble fertilizer containing humid acid and foliar fertilizer on the soilThe application of water-soluble fertilizer to greenhouse asparagus can improve soil quality to a certain extent. Soil organic matter, total nitrogen, hydrolyzable nitrogen, and available phosphorus contents increase, and soil salt content and pH value decease slightly.

4.5 Analysis of the reasons for increased production of asparagus under chemical fertilization reductionUnder the condition of compound fertilizer reduction, the main reason for the increase in production of asparagus in the greenhouse is that the fer-tilizer is directly transported to the root of the asparagus through the integrated irrigation system of water and fertilizer, and the application accuracy is higher, which is beneficial to crop absorption. At the same time, the utilization rate of fertilizer in stages is higher, and the ratio of water-soluble fertilizer to compound fertilizer is more reasonable. Conventional fertilization and topdressing are mainly based on ditch application, characterized with slow fertilizer efficiency, high waste, and low nutrient utilization efficiency. The water-soluble fertilizer adds the medium and trace elements necessary for the growth of asparagus such as calcium, magnesium, zinc, manganese and boron, which is just neglected in conventional fertilization.

In summary, the application effect of humic acid-contained water-soluble fertilizer and foliar fertilizer on greenhouse asparagus is obvious. The effect of increasing production and income is outstanding, and water and fertilizer integration can be realized, saving manpower expenditure and material consumption. Therefore, it is recommended to promote its application.