Response Measures to Climate Change to Maintain Resilient Rice Production in Taiwan ^†

Abstract

Recently, the intensification of the contrast between Taiwan’s wet and dry seasons due to climate change has led to stringent water use restrictions in agriculture, significantly impacting Taiwan’s primary staple crop, rice. This necessitates the development of effective agricultural management strategies to ensure the resilience of Taiwan’s agriculture. Therefore, we simulated potential challenges in rice cultivation due to climate change under specific conditions: flooded cultivation and soil water tension levels of −20 and −40 kPa. At −40 kPa, the soil becomes excessively dry, causing severe soil surface cracking. This results in a 20% reduction in plant height and a 30% decrease in yield compared to flooded cultivation. At −20 kPa, plant height and yield are comparable to those under flooded conditions. In resource efficiency, flooded cultivation demonstrates low irrigation water use efficiency (0.22 and 0.42 kg/m³) due to sustained high water levels. Conversely, the condition with −20 kPa shows the highest irrigation water use efficiency (2.15 and 2.16 kg/m³) with no significant difference in nitrogen use efficiency compared to flooded management. Although the irrigation water use efficiency under −40 kPa is better than flooded management (0.87 and 1.02 kg/m³), the nitrogen utilization efficiency is significantly low. Irrigation under the condition of −20 kPa climate change does not reduce yields and offers additional benefits. This strategy ensures stable crop production and conserves water resources for crop cultivation during the dry season, providing an effective means to stabilize production and mitigate the impacts of climate change on Taiwan’s agriculture.

1. Introduction

Rice (Oryza sativa L.) is the key crop in Asia, and it is eaten by half of the world’s population. The global total rice cultivation area is 168,356,566 ha, and the annual output is 799,999,504 metric tons [1]. The repercussions of global warming, a direct result of changes in the international environment, have changed the rice production landscape. Shifts in rainfall and temperatures have directly affected water storage capacity and soil moisture, while other climatic factors such as cloud cover, humidity, and evapotranspiration have further complicated the utilization and allocation of water resources. This presents a pressing challenge to rice production, necessitating immediate attention and action [2].

Taiwan has a rich environment with high temperatures and rainy weather. It has monsoon rain, orographic rain, thermal thunderstorms, typhoon rain, and tropical depression rainfall, resulting in uneven space and time distribution. Seasonal uneven distribution and long-term distribution are observed. The annual rainfall is unevenly distributed, leading to a disparity in rainfall during high and dry periods, short rivers, and poor water storage rates.

With the recent constraints on agricultural water use due to freshwater scarcity, the necessity for water-saving measures in rice cultivation has become pronounced. For instance, the implementation of the first-phase rice fallow policy in the Chianan region in 2023 and the promotion of comprehensive water-saving measures for crop rotation have far-reaching effects on issues such as rice seedling supply across Taiwan. These measures are not beneficial as they are imperative for the sustainability of rice production.

In Taiwan’s traditional paddy fields, water use progresses through three stages, from land preparation to harvesting. The first stage involves water delivery, distribution, and division, which transport water to the fields and convert it into soil moisture. The second stage is the absorption of soil moisture by crop roots, transforming it into the water the crops need. In the final stage, water enters the plant through diffusion or penetration, facilitating transport to various parts for growth and metabolism. However, significant water losses occur at all three stages, including 16 to 18% due to evaporation and 50 to 72% due to runoff and leakage, resulting in only 10 to 12% of the irrigation water being effectively utilized by the rice plants [3].

Recently, the development and implementation of climate change adaptation strategies have gained traction. In the growth stage of rice, the timing of water shortages significantly influences various yield components. For instance, water stress during the tillering stage can reduce the number of panicles per plant, while water shortages during the panicle primordium differentiation stage can decrease the number of grains per panicle. Insufficient water uptake during critical physiological stages reduces leaf water potential and photosynthesis rates, leading to a decrease in photosynthetic products, which ultimately affects both the yield and quality of rice [4].

The impacts of continuous flooding and water-saving irrigation were investigated on rice growth, yield, water use efficiency, and nitrogen use efficiency to identify irrigation practices that conserve water while maintaining stable yields.

2. Materials and Methods

2.1. Study Site and Methodology

This experiment was conducted in September 2022 (2022—2nd cropping season) and February 2023 (2023—1st cropping season) at the National Pingtung University of Science and Technology. The rice cultivar is Tainong No. 71, and the experimental site is divided into three scenario-setting areas: traditional cultivation (continuous flooding, CF) as the control group; soil water tension meter (kilopascal, kPa) readings −20 and −40 kPa were set for treatment groups; each test area was about 155 m²; and the interval between each scenario setting area was 1.5 m.

In each treatment, the water content was controlled to 2 to 3 cm on the soil surface in the first 10 days after transplanting to facilitate the stable growth of the seedlings to the survival stage. Afterward, soil moisture tensiometers (Spectrum Technologies- Irrometer Tensiometers 6420, Spectrum Technologies, Inc. Aurora, IL, USA) were embedded in the water-saving scenario test areas. Continuous flooding occurs when the water level of rice is maintained at 3 to 5 cm during the vegetative growth period. After the highest tillering period, a one-week drying period is carried out. At the beginning of the reproductive growth period, the water level is maintained at 3 cm. After the plant is stable, the water level is raised to 5 to 10 cm. The water level is lowered to 3 cm during the early stage, raised from 5 to 10 cm after earing begins, and reduced to 3 cm during the yellow ripening stage until the water is cut off 5 days before harvesting.

Water-saving cultivation includes −20 and −40 kPa in the soil water tension meter. During the vegetative growth period, it is monitored whether it has reached −20 or −40 kPa daily. If it reaches −20 kPa or −40 kPa, water is supplied. If it reaches −5–−8 kPa, the water return stops to let the value reach 0 kPa. Fertilization is provided before planting (base fertilizer), 15 days after planting, and 30 days after planting; ear fertilizer is also provided. The nitrogen ratio is 3:2:2:3 (base fertilizer: first top dressing: second top dressing: ear fertilizer) based on a nitrogen content of 120 kg/ha. The prevention and control of pests, diseases, and weeds are based on conventional agricultural methods. Water meters were installed on irrigation water pipes in each scenario setting field to record water consumption.

2.2. Sampling

The first sampling was carried out after the seedlings survived. In each setting area, 40 samples were taken for measurement at the opportunity. The plant height and relative chlorophyll content were measured every Sunday morning. After harvesting after the maturity stage, the plants in each scenario setting area were cut into a 1 × 1 m area, and two areas were randomly selected to measure parameters, such as effective tiller, grain number, fertility rate, thousand-grain weight, and yield per unit area.

2.3. Evaluation of Values

Under climate change, the stability, advantages, and disadvantages of growth and production were assessed when using water-saving or other methods for cultivation under climate change. After determining if cultivation is stable, the value of cultivation under climate change is evaluated. During the experiment, irrigation water use efficiency (IWUE) and nitrogen use efficiency (NUE) were measured. IWUE refers to the yield divided by irrigation water consumption, which is used to calculate irrigation water efficiency [5]. NUE is the yield divided by the total amount of nitrogen applied to understand the economics of nitrogen application.

2.4. Statistical Methods

All the data analysis was performed using SAS 9.4. Analysis of variance (ANOVA) was used to assess the significant differences among the data. Fisher’s Least Significant Difference (LSD) test was used to determine the significant differences with a significance level of α = 0.05.

3. Results and Discussion

3.1. Rice Growth in Different Scenarios

We recorded the effects of various water supply modes on growth traits during rice cultivation to assess the need for adjustments in cultivation practices under different scenario settings (Figure 1 and Figure 2). The control group (CF) and treatment groups with soil water tensions of −20 and −40 kPa were analyzed for differences in plant height and relative chlorophyll content. During the 2022 second cropping season (49 days after transplanting, DAT) and the 2023 first cropping season (28 DAT), plant height in the CF group was larger than in the −20 kPa and −40 kPa groups in all cultivation stages (Figure 1). The SPAD value, an indicator of chlorophyll content and photosynthetic efficiency, was lower in CF than in other treatments from 7 to 42 DAT but surpassed the scenarios of −20 and −40 kPa during the mid-growth period (49 to 56 DAT) (Figure 2). In the heading stage, the rice plant height must be between 90 and 110 cm. Too high plants show easy lodging, and too short plants yield poorly [6]. SPAD is a major indicator of plant photosynthetic efficiency. The CF scenario presents the risk of easy lodging under the −40 kPa scenario with a risk of poor yield. The rapid decline in SPAD during the reproductive growth period is crucial to carefully select the appropriate water supply pattern to balance the difficulty of cultivation with the performance of the final yield.

3.2. Post-Harvest Yield Survey

A post-harvest survey was conducted after the rice maturity period (

Table 1. The impact of different scenarios on the components and yield of rice yield.

	ET (no.)	GN (no.)	FR (%)	TGW (g)	Yield (kg/ha)
2022—2nd cropping season
CF	17.8 a	1071.0 a	70.2 a	22.6 a	3626.2 a
−20 kPa	17.3 a	1051.4 a	75.0 a	19.3 ab	3204.4 a
−40 kPa	16.1 a	604.9 b	54.9 b	18.0 b	1851.3 b
2023—1st cropping season
CF	28.2 a	1277.9 a	72.3 a	26.4 ab	4454.7 a
−20 kPa	21.9 a	1060.6 b	75.4 a	27.2 a	4709.7 a
−40 kPa	16.6 c	874.1 b	57.4 b	25.9 b	4110.9 b

Means followed by different letters within columns differ significantly at p < 0.05 according to Fisher’s LSD test. ET: effective tiller, GN: grain number, FR: fertility rate, TGW: thousand-grain weight.

). If different water supply modes were used in the two seasons of cropping, regardless of the number of effective tillers, grain number per plant, yield, and thousand-grain weight, the CF and −20 kPa scenarios had more yields than the −40 kPa scenarios. If the soil water tension remains below −40 kPa for a long time, the effective tiller number of rice reduces, thereby decreasing the yield, ultimately leading to a decrease in yield. In addition, −20 kPa allows for maintaining yield performance similar to that of CF, which is related to root biomass [7].

3.3. Feasibility Assessment

While adequate irrigation enhances rice yields, it may also lead to unproductive water loss. Reducing water supply generally decreases plant height, particularly due to restricted growth during the vegetative stage. However, the −20 kPa scenario demonstrated that appropriate water-saving irrigation can maintain yields, as there was no significant difference in yield during the second cropping season. In addition, CF increases the number of rice tillers, growth consistency, excellent growth potential, and grain number per plant, thereby increasing yield. Water also participates in important physiological functions, such as photosynthesis and protein synthesis. The CF scenario increases tillering, consistent growth, superior growth potential, and a higher grain number per plant, contributing to higher yields. Water plays a crucial role in physiological processes, including photosynthesis and protein synthesis (

Table 2. Assessment of added value in different situations.

	Irrigation Water Consumption (m3)	IWUE (kg/m3)	NUE (kg/m3)
2022—2nd cropping season
CF	135.00	0.42 c	30.22 a
−20 kPa	23.00	2.16 a	26.70 a
−40 kPa	33.00	0.87 b	15.43 b
2023—1st cropping season
CF	316.00	0.22 c	37.12 a
−20 kPa	34.00	2.15 a	39.24 a
−40 kPa	62.00	1.02 b	34.26 b

Means followed by different letters within columns differ significantly at p < 0.05 according to Fisher’s LSD test.

).

Regarding added value under different scenarios (Table 2), traditional CF cultivation exhibits a high nitrogen use efficiency but poor irrigation water use efficiency (IWUE). Given the concentration of rainfall in Taiwan, traditional CF may not be sustainable under climate change [8]. The −20 kPa scenario offers better IWUE and stable nitrogen use efficiency (NUE), making it a viable cultivation method under changing climate conditions. In contrast, the −40 kPa scenario, despite having good IWUE, has significantly poor NUE, leading to lower yields and making it a less favorable option. The −40 kPa scenario has good IWUE and significantly poor NUE, indicating that the yield is worse than in other scenarios, so it is not a better cultivation situation.

4. Conclusions

In addition to maintaining stable yields and reducing the impact of climate change on agriculture, planting methods under climate change have advantages in terms of added value. Therefore, in the face of the challenge of climate change, irrigation in the −20 kPa reduces yields and has the advantage of stabilizing production and increasing agricultural resilience under climate change.