Zhongwu ZHANG, Jianxin WANG , Yao LU, Zongyan DUAN, Rongzhen PENG, Min ZHOU,Jinghua YANG

Institute of Agricultural Resources and Environment, Yunnan Academy of Agricultural Sciences, Kunming 650205, China

Chili pepper is a typical high-efficiency vegetable, with a long growing cycle and a large demand of fertilizer, especially nitrogen,phosphorus and potassium[1].To maximize economic benefits in pepper production, a large amount of chemical fertilizer is applied by most farmers, resulting in the loss of soil nutrients, reduced fertilizer use efficiency and pollution to environment[2].

Currently, balanced fertilization has gradually attracted more and more attention of farmers[3].It is an approach to use appropriate amount and proportion of nutrients especially N,P and K at appropriate time based on nutrient demand and balance of soil-crop system, so that fertilizer supply can meet the nutrient demand of crops in time[4].Balanced fertilization greatly improves fertilizer use efficiency, significantly increases crop yield and benefits[5-6]. However, the study about balanced fertilization is still focused on the regulation of the amount and proportion of nutrients,while fertilizer supply is still not synchronized with the nutrient requirements of crops[7]. To synchronize nutrient supply and nutrient demand of crops,balanced fertilization usually needs to increase topdressed fertilizer and topdressing frequency in addition to application of basal fertiliz-er, which improves fertilizer use efficiency but greatly increases labor costs. Slow/controlled-release fertilizer can be administered as basal fertilizer, with no need for topdressing,greatly reducing fertilization frequency,amount and labor costs[8]. In addition,slow/controlled-release fertilizer can reduce nutrient release rate and environmental pollution,and improve fertilizer use efficiency[2]. So far, slow controlled release fertilizer has been widely applied to various grain crops such as rice, corn, wheat, and vegetables[7,9-12]. However, there are still some limitations for the application of slow-release fertilizer, like soil conditions,crop species and its high cost.

Therefore,in this study, field trials were carried out to compare the effects of conventional fertilization, balanced fertilization, slow-release compound fertilizer and slow-release urea fertilizer on pepper growth and NPK absorption, with an attempt to provide theoretical basis for the application of slow-release fertilizer in Yunnan, improve fertilizer use efficiency and reduce environment pollution.

Materials and Methods

Site and time

Field trials were carried out at Shizishan Village, Jiangna Town,Yanshan County of Yunnan Province(23°35′76.76″N, 104°19′39.09″E, at an altitude of 1 553 m), where had a subtropical climate, with an average annual rainfall of 990 mm, an annual average temperature of 15-16 ℃and a frost-free period of 303 d per year.However, Yanshan County was attacked by a serious drought from 2009 to 2011, while the total rainfall in 2011 till August 31 was only 519.5 mm,which was 16.7 mm less than that in the corresponding period of 2010.

On May 25, 2011, fertilizers were applied and pepper seedlings were transplanted according to experimental design, and pepper fruits were all harvested and weighed on September 27.

Soil properties

The soil tested was mountainous red soil. Before seed sowing, 1 kg of the soil at 0-30 deep was sampled at five points on an S shape and tested.It turned out that the soil contained 26.56 g/kg organic matter,1.30 g/kg total nitrogen, 78.84 mg/kg available nitrogen, 17.21 mg/ kg available phosphorus and 114.36 mg/kg available potassium.

Experimental design and fertilization

A total of 15 plots including five treatments with three repetitions were arranged by a randomized block design.Each plot was 20 m2(4 m×5 m).Treatment 1 was the blank control,without any fertilizer (abbreviated as CK);Treatment 2 adopted conventional fertilization (abbreviated as CF);Treatment 3 adopted balance recommended fertilization (abbreviated as BRF); Treatment 4 used a slow-release compound fertilizer supplemented with NAM (abbreviated as SRF), wherein, the NAM inhibitors included the core components urease inhibitor and nitrification inhibitor, and other components such as humic acid and zeolite powder; Treatment 5 used slow-release urea fertilizer(abbreviated as UF). Urea fertilizer (containing 46% nitrogen), single superphosphate(SSP, containing 16% P2O5), potassium sulfate (containing 50% K2O) and slow-release compound fertilizer supplemented with NAM (N ∶P2O5∶K2O =16 ∶8 ∶18) were products of Shandong Shikefeng Chemical Co.,Ltd.Urea extract (containing 25% nitrogen, of which 10% was urea nitrogen and 15% was ammonium nitrogen) was produced by Yunnan Plateau Ecological Engineering Co., Ltd. Fertilizer application in the five treatments was shown in Table 1.

Table 1 Amount of P2O5 and K2O applied in different treatments kg/hm2

In all the five treatments, farm manure, phosphate and potash fertilizers were used as base fertilizer. In detail, farm manure was applied at an amount of 15 000 kg/hm2, total nitrogen(N) at 4.62 g/kg, phosphorus(P2O5)at 2.24 g/kg,potassium(K2O)at 5.0 g/kg. In Treatment 2, 20% of nitrogen fertilizer was used as base fertilizer,40% was top-dressed at seedling stage and 40% at rosette stage. In Treatment 3, 20% was applied as base fertilizer,20%was top-dressed at seedling stage, 40% at rosette stage and another 20%at flowering stage.In Treatment 4 and Treatment 5, 60%slow-release urea fertilizer was applied as base fertilizer and 40% at flowering stage.

Planting specification and field management

A local chili pepper variety was planted. The seedlings were transplanted at a density of 60 000 seedlings/hm2, spacing 0.4 m in rows and lines.There were 10 rows in each plot and 12 seedlings in each row.

Conventional field managements were conducted during experimental period.

Sample collection and measurement

At harvest,five entire plants on an S-shaped line in each plot were sampled,and the weights of their fresh and dried roots, fruits, stems and leaves were respectively measured, before their N, P and K contents were analyzed to calculate nutrient accumulation and utilization rate using following formulas: Nutrient accumulation =Biomass × Nutrient content / 1 000;Nutrient utilization = (Nutrient absorption in fertilization treatment - Nutrient absorption of blank control ) / Nutrient input in fertilization treatment.

The contents of total nitrogen, total phosphorus and total potassium in root, stem and fruit were respectively measured using Nessler’s reagent colorimetry, vanadate-molybdate-yellow colorimetry and flame photometry after H2SO4-H2O2boiling.The contents of soil organic matter, total nitrogen,available nitrogen, available phosphorus and available potassium were respectively measured through potassium dichromate oxidation, semimicro-Kjeldahl method, alkaline hydrolysis,Mo -Sb colorimetry and flame photometry. Soil pH was measured using a pH sensor.The total nitrogen,phosphorus and potassium in farmyard manure were respectively determined using semimicro-Kjeldahl method,vanadium-molybdenum colorimetric method and flame photometry[13].

Data processing

EXCEL and DPS software adopted for multiple comparisons and correlation analysis.

Results and Analysis

Effects of slow-release fertilizer and balanced fertilization on pepper yield and dry matter accumulation

As shown in Table 2, the stem and leaf, root, fruit and total dry weights of peppers in all fertilization treatments were significantly higher than those in control. Compared to control, the total dry weight of Treatment 2 - Treatment 5 was increased by 51.18% , 65.33% , 63.4% and 59.27%; the fruit dry weight (or economic yield) was increased by 48.32%,79.38%,74.28%and 69.88%;the root dry weight was increased by 40.61%,30.83%,30.88%and 37.91%;the leaf dry weight was increased by 58.82%,52.97%,55.53%and 48.56%.The fruit dry weight in Treatment 3-Treatment 5 was 20.94%, 17.5% and 14.54% greater than in Treatment 2,while the root and total dry weights had no significant difference among all fertilization treatments.

In summary, fertilizers significantly improves the dry matter accumulation in pepper plants;balance fertilization and two slow-release fertilizers had better effects on dry matter accumulation in pepper fruit than conventional fertilization, but the dry matter accumulation in aboveground part and root did not exhibited significant differences among these fertilization treatments.

Effects of slow-release fertilizer and balanced fertilization on nitrogen absorption in different parts of pepper plant

As can be seen from Table 3, the cumulative nitrogen uptake in root,fruit, stem and leaf and the total nitrogen uptake of pepper plant in all fertilization treatments were significantly higher than those of control. Compared with control, the total nitrogen uptake in Treatment 2 - Treatment 5 were increased by 51.47%, 79.62%,66.12% and 60.01%; the fruit nitrogen uptake was increased by 47.64% ,79.43%,74.89%and 67.12%;the root nitrogen uptake was increased by 59.56%,40.45%,51.30%and 54.83%;the nitrogen uptake in stem and leaf was increased by 61.66%, 88.86%,41.99% and 38.97%. Compared with Treatment 2, the nitrogen uptake in fruit of Treatment 3-Treatment 5 was increased by 21.53% , 18.46% and 13.19%, respectively, while the nitrogen uptake in root, stem and leaf was significantly increased in Treatment 3,but was little increased or even was decreased in other treatments.The nitrogen content pepper fruit in all fertilization treatments was significantly higher than that in control, but there was no significant differences among these fertilization treatments. Slow-release fertilizer greatly improved the nitrogen content in stem and leaf, but there was no significant difference among other fertilization treatments.The N use efficiency in Treatment 3-Treatment 5 was 5.84%, 7.14% and 8.33%greater than that of treatment 2.

The nitrogen content in different parts of pepper plant from large to small was fruit＞stem and leaf＞root,wherein the nitrogen content in fruit was significantly greater than that in root and stem, and the nitrogen content in root and stem had little difference. The cumulative nitrogen uptake in different parts of pepper plant from large to small was fruit ＞stem and leaf ＞root, wherein fruit nitrogen uptake was significantly greater than stem nitrogen uptake, and the latter was also significantly greater than root nitrogen uptake.

Table 2 Comparisons of yield and dry matter accumulation of different parts of driedpeppers kg/hm2

Table 3 Comparisons of nitrogen content and uptake amount of different parts of pepper plant

Effects of slow-release fertilizer and balanced fertilization on phosphorus absorption in different parts of pepper plant

It could be concluded from Table 4 that the cumulative phosphorus uptake in stem and leaf,root,fruit and total phosphorus uptake of pepper plant in all fertilization treatments were significantly higher than those of control.Compared with control,the total phosphorus uptake in Treatment 2-Treatment 5 were increased by 49.03% ,68.31%, 67.7% and 58.32%; the fruit phosphorus uptake was increased by 46.96%, 67.65%, 70.11% and 62.3%;the root phosphorus uptake was increased by 63.65%, 30.75%, 50.81%and 42.75% ; the leaf phosphorus uptake was increased by 61.56% ,80.82%, 53.14% and 31.67%. Compared with Treatment 2, the phosphorus uptake in fruit was significantly im-proved by 14.08% , 15.76%and10.44% in Treatment 2 - Treatment 5, while the phosphorus uptake in root was reduced; phosphorus uptake in stem and leaf of Treatment 3 was increased by 11.92%, but that in Treatment 4 and Treatment 5 was decreased. Fertilizers had little effect on fruit phosphorus content, and the fruit phosphorus content showed no significant difference among these fertilization treatments. The stem phosphorus content in Treatment 3 was significantly higher than in other treatments,while there was no significant difference among other treatments. The root phosphorus content in Treatment 2 and Treatment 4 was significantly higher than in other treatments, while there was no significant differences among other treatments.The phosphorus fertilizer use efficiency was relatively low in all treatments. The phosphorus fertilizer use efficiency in Treatment 3 - Treatment 5 was 3.32% ,3.27% and 2.47% higher than that in Treatment 2.

The phosphorus content in different parts of pepper plant from large to small was fruit＞stem and leaf＞root,wherein the phosphorus content in fruit was significantly greater than that in root and stem, and the nitrogen content in root and stem had little difference. The cumulative phosphorus uptake in different parts of pepper plant from large to small was fruit＞stem and leaf ＞root, wherein fruit phosphorus uptake was significantly greater than stem phosphorus uptake, and the latter was also significantly greater than root phosphorus uptake.

Table 4 Comparisons of phosphorus content and uptake amount of different parts of pepper plant

Table 5 Comparisons of potassium content and uptake amount of different parts of pepper plant

Effects of slow-release fertilizer and balanced fertilization on potassium absorption in different parts of pepper plants

As shown in Table 5,the cumulative potassium uptake in stem and leaf,root,fruit and total potassium uptake of pepper plant in all fertilization treatments were significantly higher than those of control. Compared with control, the total potassium uptake in Treatment 2 - Treatment 5 were increased by 61.61%, 72.81%, 70.81%and 65.61%; the fruit potassium uptake was increased by 52.87% ,87.52%,76.92%and 77.77%;the root potassium uptake was increased by 40.68%, 26.83%, 33% and 46.54%;the stems potassium uptake was increased by 80.25%, 54.31%, 66.08%and 47.3% . Compared with Treatment 2, the potassium uptake in fruit was significantly improved by 22.66%,15.73% and 16.28% in Treatment 2 -Treatment 5, while the potassium uptake in root and stem was reduced.Fertilizers had slight effect on the potassium uptake of pepper root, fruit,stem and leaf, and the fruit potassium content showed no significant difference among these fertilization treatments.The stem potassium content in Treatment 2 and Treatment 4 was significantly higher than in other treatments, while there was no significant difference among other treatments.The root potassium content in Treatment 4 was significantly higher than in other treatments, while there was no significant differences among other treatments. The potassium fertilizer use efficiency in Treatment 2 - Treatment 5 was 34.43%, 20.35%, 16.6%and 18.33%, indicating that Treatment 3- Treatment 5 promoted potassium uptake, but reduced the use efficiency of potassium fertilizer due to the increased fertilizer application.

The potassium content in different parts of pepper plant from large to small was fruit＞stem and leaf＞root,wherein the potassium content in fruit and stem had little difference, both significantly greater than that in root.The cumulative potassium uptake in different parts of pepper plant from large to small was fruit ＞stem and leaf＞root,wherein fruit potassium uptake was significantly greater than stem potassium uptake, and the latter was also significantly greater than root potassium uptake.

Discussion and Conclusions

The results showed that the two slow-release fertilizers we tested promoted the dry matter accumulation in pepper root and fruit, and greatly increased pepper yield, which agreed well with previous studies[14-15]. The study of Tang et al.[2]applying slow-release fertilizer once or twice during pepper growth period completely met the nutritional demands of pepper,im-proved pepper root activity,N,P and K fertilizer use efficiency. The present study revealed that both slow-release compound fertilizer and slow-release urea fertilizer greatly increased nitrogen use efficiency of pepper by 50%,compared with conventional fertilization, because by controlling nitrogen release rate slow-release fertilizer improved soil fertility and enzyme activity at late growth stage, thus improving crop growth and yield[15-16]. Slow/controlled release fertilizer had higher use efficiency than urea as base fertilizer,and similar result was also reported by Huang et al.[14,17]. We also found that both slow-release compound fertilizer and slow-release urea fertilizer improved phosphorus use efficiency.However,the nitrogen use efficiency of the two fertilizers was only 14.59%,significantly lower than 44.4% in the study of Huang et al.[14],and the phosphorus use efficiency was even lower,only about 5% . Continuous drought and large fertilizer application may be two main reasons causing such low fertilizer use efficiency.

We also found balanced fertilization and slow-release fertilizer had similar effects on pepper yield and the uptake of nitrogen and phosphorus,indicating that slow-release fertilizer not only improved the use efficiency of nitrogen and phosphorus, but also reduced fertilizer amount (especially nitrogen fertilizer),fertilization frequency,labor costs and environmental pollution caused by fertilizers. In addition,the effects of the two slow-release fertilizers on N, P and K uptake in different parts of pepper plant were also investigated, and the results revealed that the content and uptake of N, P and K showed an order of fruit＞leaf＞root, among which, the content and uptake of N, P and K in fruit were significantly higher than in root and stem,and the uptake of N, P and K in stem was also significantly higher than in root.

In summary, compared with the conventional fertilization in pepper planting area of Yunnan Province, balanced fertilization and slow-release fertilizer can improve pepper yield, the uptake of N,P and K,fertilizer use efficiency,and thus reduce nitrogen fertilizer application, environmental pollution and labor costs.

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