Abstract

Fertilizer plays an important role in increasing rice yield. More than half of all fertilizer applied to the field is not taken up, resulting in environmental damage and substantial economic losses. To address these concerns, a low-cost, coated compound fertilizer named “Xiang Nong Da” (XND), requiring only a single basal application, was studied. A two-year field experiment was conducted to test the effects of XND application on rice yield and nitrogen fertilizer use efficiency. An ordinary uncoated compound fertilizer (UNCF), with 20% more nutrients and split application was selected as the control. The yield of XND-treated rice was only 3.1% lower than that of the control, an insignificant difference. There were no significant differences between N use efficiency indices of the two fertilizer treatments except for N partial factor productivity (PFP N). PFP N of XND treatment was 19.7%–23.2% higher than the control, a significant difference. This result indicates that a 20% decrease in N application rate is possible with XND without yield reduction and with savings in both labor and time.

Keywords

Rice; Yield; Fertilizer; Nitrogen use efficiency

1. Introduction

Rice is the main staple food for > 60% of China’s population [1]. Fertilizer is a determining factor for rice growth and plays a vital role in maintaining rice yield. Increased fertilizer application has contributed significantly to improved rice yield [2, 3, 4]. Although fertilization drives productivity, nitrogen use efficiency in rice production is very low, with nitrogen use efficiency in China averaging only 27.5% [5]. High external N input and ineffective fertilization practices have led to low nitrogen use efficiency [2, 3, 6, 7]. Leaching, runoff, and volatilization are the major N loss pathways. Besides the low nitrogen use efficiency, excessive fertilizer in fields harms the environment by increasing the greenhouse effect, soil degradation, and groundwater pollution [8]. In view of the present situation, many N conservation application practices such as balanced N fertilization, site-specific N management, integrated N management, nitrification inhibitor use, and controlled-release fertilizers (CRF), have been developed to improve nitrogen use efficiency [7, 9, 10]. Recently, the use of CRF has become common to lessen fertilizer consumption, increase nitrogen use efficiency, and minimize environmental pollution [9, 11, 12]. CRF is a type of fertilizer that controls the rate of nutrient supply. It is a polymer-coated fertilizer, generally a compound fertilizer or urea coated with polymer [13]. Many studies have found that CRF applications significantly increase nitrogen use efficiency and crop yield [14, 15]. They are also more environmentally friendly fertilizers, because the N losses through leaching and denitrification are reduced [16, 17, 22, 23]. Conventional fertilization requires frequent applications, whereas a CRF needs only a single application and is thus more labor and time saving than conventional fertilization.

Thus, study of controlled-release fertilizer techniques is important for increasing rice yield and fertilizer efficiency. The present study investigated a low-cost, coated compound controlled-release fertilizer, “Xiang Nong Da” (XND), comparing yield and N use efficiency of test rice cultivars treated with XND or a conventional compound fertilizer with two applications, XND supplied 20% fewer nutrients in the test. The study’s objectives were to investigate the effects of XND treatment on rice yield and N use efficiency.

2. Materials and methods

2.1. Site description

Field experiments were conducted during the early season (late March to July) and the late season (mid-June to late October) in 2014 and 2015 in the same field located in Liuyang county, Hunan province, China (28°09′N, 113°37′E, 43 m.a.s.l.).

In 2014 before the experiments, experimental site soil samples were collected from the upper 20 cm. The soil was clayey with pH 6.25, 23.49 g organic C kg − 1 , 1.24 total N kg − 1 , 18.24 mg kg − 1 available P, and 112.71 mg kg − 1 available K.

2.2. Genetic material

An early-season rural conventional rice variety “Zhongjiazao 17” was used for early-season experiments. A late-season hybrid rice variety “Shengtaiyou 9712”
(Shengtaiyou A × 9712) was used for late-season experiments. These are major cultivars currently widely used in China’s Yangtze River valley.

2.3. Experimental design

The experimental design was a completely randomized block with 3 replicates.
Each plot had an area of 4 m × 5 m. Three fertilizer treatments were applied:
T1: a control with no N application.
T2: an ordinary compound fertilizer, N–P 2 O 5 –K 2 O (20–5–10), produced by Hunan Hua Lu Company, at an N rate of 135 kg ha − 1 .
T3: XND, a controlled-release fertilizer, N–P 2 O 5 –K 2 O (20–5–10), a low-cost, self-developed polymer-coated compound fertilizer [17], produced by Hunan agricultural university, at an N rate of 108 kg ha − 1 .

XND (T3) was used as basal fertilizer once before planting rice. The ordinary fertilizer (T2) was applied as a split application at two rice developmental stages:
one (50%) at preplant and other (50%) at the tillering stage. P and K fertilizers in the T1 treatment were applied as basal dressings at the rate of 34 (P 2 O 5 ) and 68 (K 2 O) kg ha − 1 , and were applied in T2 and T3 at the same rate.
The nursery field was prepared one week before sowing. The compound fertilizer (nutrient content > 35%) was applied to the nursery field at a rate of 450 kg ha − 1 before plowing. Germinated seeds were sown in nursery beds at a rate of 30 g m − 2 on May 23 for early season and June 27 for late season in both years. They were transplanted to a spacing of 20.0 cm × 16.5 cm, with three seedlings per hill. Seedling age at transplanting was 30 days in early season and 24 days in late season. The water regime management was in the sequence of shallow irrigations (2–3 cm), midseason drainage (10–15 days), and shallow irrigation. Pests and diseases were controlled using chemicals. Weeds were controlled using herbicides and hand pulling.

2.4. Measurement and sampling

2.4.1. Dry matter, yield, and yield components

Six hills were diagonally sampled from each subplot at full heading stage (when about 80% of the panicles had emerged from the flag leaf sheath). Samples were separated into leaves, stems, and panicles. Each part was oven-dried in an oven at 75 °C to constant weight.
At physiological maturity, in the middle of each subplot, ten hills of plants were diagonally sampled. Panicles were counted to calculate panicles m − 2 . Plant
samples were separated into panicles and straw (including rachis). Panicles were hand-threshed. Unfilled spikelets were then separated from filled spikelets by
submersion in water. Three 30 g subsamples of filled grain and all unfilled spikelets were manually counted. Straw and filled and unfilled spikelets were
oven-dried at 75 °C to constant weight. Spikelets per panicle, spikelet filling percentage, and harvest index were then calculated. Grain yield was obtained
from a 5 m 2 area in each plot and adjusted to the standard moisture content of 0.14 kg H 2 O kg − 1 .

2.4.2. Leaf area index [LAI] and N content

A leaf area meter (LI-3000, LI-COR, Lincoln, NE, USA) was used to measure the green leaf area at full heading stage and LAI was calculated leaf area/unit ground area.
N concentrations in stem, filled and unfilled, were measured with a Skalar SAN Plus segmented flow analyzer (Skalar Inc., Breda, The Netherlands). N uptake
was calculated by biomass multiply N content. Nitrogen fertilizer use efficiency indices were calculated as follows:

Calculation of Nitrogen fertilizer use efficiency indices. Dark Green Singularity - blog about leaf area measurement

where TN + N = N total accumulation of aboveground plants in the plot that received N fertilizer; TN − N = total N accumulation of aboveground plants in the zero-N control; FN = the amount of N fertilizer applied; GY + N = grain yield in the plot that received N fertilizer; GY − N = grain yield in the zero-N control.

2.5. Data analysis

Data were analyzed by analysis of variance (Statistix 8.0, Analytical Software, Tallahassee, FL, USA), and significant differences between means were identified by the Least Significant Difference test at the 0.05 probability level.

2.6. Climatic conditions

Maximum and minimum temperatures for the experimental periods within the season followed the same trends in both years (Fig. 1). In the early season,
maximum and minimum temperatures increased between transplanting and maturity. In the late season, temperatures between transplanting and maturity
decreased. For both years in both seasons, experimental period average maximum and minimum temperatures were approximately 30 °C and 22 °C.

Fig. 1. Daily maximum and minimum temperatures during the experimental period. Dark Green Singularity - news about leaf area measurement

Fig. 1. Daily maximum and minimum temperatures during the experimental period.

3. Results

3.1. Grain yield and yield attributes

There was no significant difference in grain yield between T2 and T3 in both years and seasons. But these yields were significantly higher than those of T1 (Table 1). T2 consistently reached the highest yield regardless of year or season.

Table 1. Grain yield, yield components, total biomass production, and harvest index under three fertilizer treatments in 2014 and 2015.

Table 1. Grain yield, yield components, total biomass production, and harvest index under three fertilizer treatments in 2014 and 2015.

Within each column, values followed by different letters are significantly different at the 0.05 probability level according to Least Significant Difference test.

There were significant differences between the zero-N treatment (T1) and the N treatments (T2, 135 kg ha − 1 , T3, 108 kg ha − 1 ) in panicles m − 2 (Table 1). The ranking across years and seasons was as follows: T2 > T3 > T1. T2 consistently produced more panicles m − 2 regardless of year or season, but significantly more than T3 only in the 2014 late season. Spikelets per panicle were fewer in T1 than in the other two treatments in both years and seasons except for the 2014 early season. There were significant differences in spikelets per panicle between T2 and T3 in the 2014 late season. Grain-filling percentage was slightly higher in T1 than in other treatments for 2015, but not 2014. The ranking across different years and seasons was as follows: T1 > T2 > T3. Grain weight among treatments was not consistent and did not show an identifiable trend.
T1 total biomass production was significantly lower than that of the other two treatments for all years and seasons, with no significant differences between T2
and T3. T3 was always higher than T2 except in 2014 early season. Differences in harvest index between T2 and T3 were insignificant.

3.2. N uptake and N use efficiency

T2 achieved the greatest total N uptake regardless of year or season (Table 2), but it was not significantly higher than that of T3. AE N , RE N , PE N , and PFP N were higher in T3 than in T2 for all years and seasons. There were no significant differences in AE N or PE N between T2 and T3. The PFP N of T3 was significantly higher except in 2014 late season.

Table 2. Total N uptake, applied N agronomic efficiency (AE N ), applied N crop recovery efficiency (RE N ), applied N physiological efficiency (PE N ), and applied N partial factor productivity (PFP N ) under three fertilizer treatments in 2014 and 2015.

Table 2. Total N uptake, applied N agronomic efficiency (AEN), applied N crop recovery efficiency (REN), applied N physiological efficiency (PEN), and applied N partial factor productivity (PFPN) under three fertilizer treatments in 2014 and 2015.

Within each column, values followed by different letters are significantly different at the 0.05 probability level according to Least Significant Difference test.

3.3. LAI

LAI at flowering was significantly different between treatments. T1 showed the lowest LAI at flowering across all years and seasons (Fig. 2). During 2014 late
season and 2015 early season, LAI at flowering was significantly higher in T3 than in T2. There was no significant difference between T2 and T3 in 2014 early season and 2015 late season. Generally, LAI at flowering among treatments showed a similar ranking (T3 > T2 > T1) across all years and seasons.

Fig. 2. Leaf area index (LAI) of early and late season rice under three fertilizer treatments in 2014 and 2015.

Fig. 2. Leaf area index (LAI) of early and late season rice under three fertilizer treatments in 2014 and 2015.

4. Discussion

N loss is a severe problem in rice cultivation. Nitrogen use efficiency in rice is often low as a result of high N loss through volatilization, leaching, and denitrification.
Controlled-release fertilizers generally outperform granular urea fertilizer in reducing N losses, stimulating plant growth, and increasing nitrogen use efficiency
[12]. Yang et al. [18] reported that using controlled-release urea (CRU) in rice without additional fertilizer application during the growing season significantly
increased N availability in soil and improved yields by 13.6%–26.5%. In the present study, the rice yield was 3.1% lower under XND treatment than under
ordinary compound fertilizer treatment, but XND requires only one application and is more labor and time saving than standard compound fertilizers, which require split fertilization. The labor cost of fertilization of XND was only half that of the ordinary compound fertilizer.
Considering the negative impact of over fertilization on grain yield, damage to the environment, and decrease in nitrogen use efficiency and grain quality, it is
desirable to pay more attention to reducing fertilizer inputs in rice production in China [6, 19, 20]. Gen et al. [21] found that reducing the CRU rate by 30% produced the same crop yield as with the 100% rate of urea, and rice yield under a CRU 50% treatment showed no significant difference from that under a urea 100% treatment. In our experiment, XND treatment supplied only 80% of the N amount of standard compound fertilizers.
The application of controlled release fertilizer can increase rice production by increasing the number of panicles m − 2 and spikelets per panicle [22, 23]. In the
present study, analysis of yield components indicated that XND rice yield did not decrease significantly, owing to larger panicle size (spikelets per panicle). Equal total biomass production was responsible for the similar grain yield between the two treatments.
There have been consistent findings that controlled-release fertilizer can improve nitrogen use efficiency in rice production compared with regular fertilizer
[12, 14, 18, 24]. Nitrogen use efficiency is a widely used index in evaluating fertilizer management efficiency, and it can be further separated into different component indices to represent diverse aspects [25, 26]. In this study, there were no significant differences between N use efficiency indices of the two fertilizer treatments except for PFP N , which is an aggregate efficiency index that includes contributions to grain yield derived from indigenous soil N uptake, fertilizer N uptake efficiency, and the efficiency with which N acquired by the rice plant is converted to grain yield [27]. Tang et al. [28] showed that at 30 days after fertilization, single basal application of controlled-release fertilizers increased soil available N by 147.9% in comparison to a control treatment. That author indicated that the main mechanisms for increasing rice yield using a single basal application of controlled-release fertilizers should be attributed to greater soil N supply availability. Thus, in the present study, the similarly high yield from XND treatment may have been driven mainly by indigenous soil N and not by fertilizer N. But we did not measure the variety of soil N content after applied the CRF. Further studies are needed to explain the mechanisms of increase in rice yield using XND.

5. Conclusion

XND, a one-time basal fertilizer (80% N), achieved nearly identical yields to uncoated compound fertilizer used in a split application (100% N). It showed
consistently higher values than the control for partial factor productivity of N (PFP N).·This finding supports the conclusion that controlled release fertilizers such as XND should be explored as a partial substitute for common fertilizers in order to obtain sustainable increases in crop yields and decrease labor costs.

Acknowledgments

This research was supported by the Special Fund for Agro-scientific Research in the Public Interest (201303103) and China Agriculture Research System (CARS-01).

References

© 2017 Crop Science Society of China and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V.

Original Text: link

Original Reference: The Crop Journal, Volume 5, Issue 3, June 2017, Pages 265-270