Impact of climate fluctuations on paddy yield - A case study in Kollengode Village

In the south Indian state of Kerala, Palakkad district cultivates rice on over 300 km2 of land, contributing significantly to the state’s agricultural output with an annual yield of around 90,000 tons.

Stages in paddy cultivation

Paddy cultivation can be broadly divided into three key stages based on the plant’s development:

1. Vegetative stage: This is the initial stage after germination, and is marked by growth and development of the leaves and root system. The stage typically lasts for about 50– 60 days, depending on the rice variety and growing conditions.
2. Reproductive stage: This stage marks the shift from vegetative growth to grain production. It consists of three substages:
   • Heading stage: The panicle (flowering head) emerges from the uppermost leaf sheath, signalling the start of flower development. This stage usually lasts for around 7–10 days. 
   • Flowering stage: The flowers within the panicle open and pollination occurs. This stage typically lasts for 5–7 days.
   • Milking stage: The fertilised flowers begin to develop into grains, initially appearing milky-white in colour. This stage lasts for about 20–30 days.
3. Maturity stage: This stage involves the grains ripening and turning golden in colour. It typically lasts for 20–30 days, depending on the variety. The timing and duration of each stage can vary depending on several factors, including the specific rice variety, climatic conditions, and agricultural practices. 

General factors affecting paddy yield

Numerous elements contribute to the final success of a paddy harvest, such as rainfall, groundwater levels, soil characteristics, the chosen rice variety, implemented crop management practices, prevailing temperature, and the presence of pests and diseases.

• Rainfall : Rainfall directly impacts paddy productivity, playing a critical role in determining crop yield. Insufficient rainfall throughout the growing season, particularly during the vegetative stage, can trigger drought conditions and negatively impact yield. Conversely, excessive rainfall during the heading and flowering stages can be detrimental, potentially delaying grain filling and harvest. Ideally, paddy thrives in regions receiving 1,000–1,500 mm of annual rainfall, ensuring abundant water throughout the vegetative stage while avoiding detrimental flooding during later stages.
• Groundwater : Groundwater plays a crucial role in paddy cultivation, directly impacting crop yield and overall agricultural productivity. While the relationship is complex and influenced by various factors, the availability and quality of groundwater can significantly affect rice growth and development.
  • Positive impacts 
    • Reliable water source: When groundwater levels are adequate, they provide a dependable source of irrigation water, especially during drier periods when rainfall is insufficient. This ensures consistent moisture availability throughout the growing season, crucial for optimal plant growth and yield potential.
    • Nutrient availability: Groundwater often contains dissolved nutrients essential for plant growth, such as nitrogen, phosphorus, and potassium. Access to these nutrients through groundwater uptake can supplement fertilisers and enhance yield potential.
  • Negative impacts
    • Drought stress: Depleted groundwater levels can lead to drought stress, impacting plant growth and development. Inadequate water availability during critical stages like tillering (shoot branching) and grain filling can significantly reduce yield.
    • Salinity intrusion: In coastal regions, excessive groundwater extraction can cause saltwater intrusion, increasing water salinity. This can adversely affect rice plants, reducing yields and even leading to crop failure.
    • Nutrient imbalance: Changes in groundwater quality due to factors like pollution or natural variations can affect nutrient availability and uptake by plants. This can lead to nutrient deficiencies or imbalances, hindering plant growth and impacting yield.
• Soil characteristics : Soil characteristics, such as texture, bulk density, and pore space, play a critical role in influencing paddy yield. A balanced texture, ideally a loamy mix (a good proportion of sand, silt, and clay particles), allows for optimal root penetration, air circulation, and water retention. Conversely, heavy clay soils can hinder drainage, while sandy soils drain too quickly. Bulk density, the weight of soil per unit volume, affects the available pore space. Loose, well-aggregated soil with moderate bulk density ensures both adequate air for root respiration and sufficient water holding capacity. Conversely, dense and compacted soils restrict air and water availability, hindering plant health. Ultimately, texture and bulk density influence the soil’s water retention capacity, the ability to hold water for plant use. Clay-rich soils hold more water, but excessive levels can be detrimental. Sandy soils drain quickly, potentially leading to drought stress. A balance between these extremes is crucial for optimal paddy growth.
• Rice variety : Rice variety plays a significant role in paddy yield, with different varieties having different inherent yield potentials based on genetic factors like tillering ability, grain size, and disease resistance. Some varieties are better adapted to specific climates, soil types, and water availability than others. Choosing varieties suited to local conditions can significantly improve yield. Varieties with shorter growth durations can fit multiple cropping cycles within a year, potentially increasing overall yield.
• Crop management practices : Implementing crop management practices like proper tillage, optimal planting density, judicious fertiliser use, efficient water management, intercropping, and crop rotation fosters healthy soil, breaks disease cycles, manages pests, and promotes sustainable, high yields. Tilling the soil loosens it, allowing for better root penetration, air and water circulation, and drainage; however, it can also disrupt soil structure and accelerate the breakdown of organic matter, leading to reduced soil fertility and water retention capacity. Therefore, tillage should be done with care, minimising soil disturbance to maintain longterm soil health. Optimal plant density ensures proper compe tition for resources like light and nutrients while avoiding overcrowding that can hinder growth.
  Intercropping, the practice of growing two or more crops together in close proximity, offers numerous benefits. Different crops can occupy different niches within the same field, potentially leading to higher overall yield from the combined crops. As different crops have varying nutrient requirements and root depths, one crop can utilise nutrients that are less accessible to the other, maximising nutrient uptake and minimising waste. Some intercropping combinations can help manage water resources. For example, taller crops can provide shade and reduce water evaporation from the soil, benefitting shorter companion crops. Intercropping can also suppress weeds and lead to improved pest and disease control, since a diverse selection of plants in the field can disrupt the life cycle of pests and diseases adapted to a single crop. Intercropping, particularly with cover crops, can help protect the
  soil from wind and water erosion, crucial for maintaining soil fertility and long-term productivity. The root systems of different intercropped plants can create a more complex and diverse soil structure, promoting aeration and drainage, which benefits overall soil health.
• Temperature : Rice plants thrive within a specific temperature range, ideally between 20 °C and 35 °C, although this optimal range can vary slightly depending on rice variety and specific climatic conditions. Deviations from this optimal zone, whether higher or lower, can significantly impact plant development and ultimately, yield. The temperature fluctuations influence the timing and pace of various growth stages, affecting growth rate and overall yield potential. The severity of these impacts depends on both the intensity and duration of the temperature shift. Temperatures exceeding 35 °C stress the root and shoot system, hampering their growth and impacting nutrient uptake. This, in turn, hinders vital reproductive processes like pollination and pollen release, potentially leading to poor fertilisation and ultimately resulting in unfilled grains (spikelet sterility). Prolonged exposure to such heat further amplifies these problems by directly disrupting pollen release, pollination, and germination. 
  Additionally, high temperatures shorten the critical grain filling period, further reducing yields. On the other hand, temperatures below 20 °C primarily impact earlier growth stages and development. Cold temperatures slow down metabolic processes, delaying seed germination and seedling establishment. This can later lead to uneven stands (crop fields where the plants are unevenly distributed in terms of density, growth stage, or health) and
  reduced tillering. Additionally, flowering may be disrupted, resulting in incomplete grain development in the panicle. Ultimately, these issues contribute to lower yields, although through distinct mechanisms compared to high temperatures.
• Pests : Numerous insects pose threats to rice plants, including planthoppers (e.g., brown planthopper, white-backed planthopper) and leafhoppers (e.g., green rice leafhopper, black leafhopper). These insects primarily harm rice through the transmission of viral diseases, but they also damage plants by feeding on them and excreting honeydew. Other damaging insects include stem borers (e.g., yellow stem borer, white stem borer) and gall midges (e.g., Asian rice gall midge). Stem borers feed on the plant’s internal tissues, disrupting their structure and function. Gall midges manipulate the plant’s growth hormones, leading to abnormal gall formation and hindering functionality. However, it is important to note that not all species within these groups are detrimental; some even play beneficial roles. The presence of beneficial insects (decomposers, scavengers, etc.), pollinators, and natural enemies of pests can in fact contribute to yield improvement. In addition to the insects mentioned above, other potential threats depending on the region and  circumstances include weevils, armyworms, grasshoppers, and thrips. Rootfeeding nematodes, which are microscopic worms ranging from a few micrometres to millimetres, can damage plant roots and hinder growth. Snails and slugs feed on young seedlings and leaves, potentially affecting plant establishment. Vertebrates can also be significant pests. Rats and mice can cause substantial yield losses by feeding on grains and stems. Some bird species consume rice grains at various stages, impacting yields.
• Diseases : In general, fungal diseases like rice blast, sheath blight, and brown spot are among the most widespread and damaging globally for paddy plants. These diseases affect various plant parts (leaves, stems, grains) and can result in significant yield loss. However, the relative importance of fungal, bacterial, and viral diseases can vary depending on the specific region, rice variety, and climate. Bacterial diseases like leaf blight, leaf streak, grain rot, and panicle blight can be significant in specific regions or under certain conditions. Viral diseases transmitted by insect vectors, like rice tungro disease complex (transmitted by leafhoppers) and rice ragged stunt virus (transmitted by white-backed planthoppers), can also cause widespread damage and stunted growth if vector populations are high.
• Additional environmental influences : Apart from the previously mentioned factors, several other environmental elements can impact paddy yields:
  
  • Day length (photoperiod): The duration of sunlight during the growing season influences various physiological processes in rice plants, including flowering time, tillering, and grain filling. Depending on the rice variety and its sensitivity to photoperiod, shorter or longer days may lead to reduced yield potential.
  • Extreme weather events: Strong winds, hailstorms, and floods associated with extreme weather events can physically damage rice plants, causing lodging (falling over), shattering of grains, and reduced yield.
  • Air quality: Air pollution from industrial activities or agricultural practices can negatively impact plant growth and development. Pollutants like ozone, sulphur dioxide, and heavy metals can reduce photosynthesis, damage leaves, and hinder grain filling, ultimately leading to yield losses.

Paddy cultivation in Kollengode village

Kollengode village is a major agricultural village located within the Palakkad district of Kerala State in south India. Paddy cultivation is a cornerstone of Kollengode’s economy, encompassing roughly 10,000 hectares of land and providing a livelihood for more than 6,000 families. Farms in the region are predominantly small-scale, with most farmers cultivating 1–2 hectares. A small number of larger farms exceeding 5 hectares also exists. This region experiences a humid climate with distinct seasons: a hot period (March– May), followed by the southwest monsoon (June–September) characterised by heavy rainfall, and the northeast monsoon (October–November) with moderate precipitation. The remaining months (December–February) are relatively dry. The annual  temperature ranges from 20 °C to 45 °C.

Rice is typically cultivated in two distinct seasons: Kharif, the monsoon season from June to October, and Rabi, the winter season from November to March [6]. The seeds for the Kharif season are normally sowed in late May in anticipation of the southwest monsoons that start on 1 June. However, during the past two years, delayed monsoon onsets have necessitated a shift in seed sowing and harvesting dates. Additionally, there has been a concerning decline in paddy yields in Kollengode, prompting investigations into the underlying causes. The two rice varieties, Uma Matta and Jyoti Matta, are cultivated in two distinct seasons:
Kharif (June–October, rainfed harvest in October) and Rabi (November–March, irrigated harvest in March).

Factors affecting yield of paddy in Kollengode Village

Investigation explored several potential causes for the observed paddy yield decline, focusing on climatic factors (rainfall, temperature), agricultural practices (rice varieties, crop management), and environmental influences (soil properties, pest and disease incidence, air pollution, sunlight duration).

Notably, significant reduction in rainfall during the critical growing season is likely the primary contributor. Decreased water availability can also make rice plants more susceptible to the effects of nighttime warming, potentially leading to increased respiration rates and reduced yields.

Water saving measures taken by farmers

Kollengode farmers already employ several water-saving practices in their crop management, as reported by the farmers themselves. These practices include alternate wetting and drying (AWD), the System of Rice Intensification (SRI) method, and raising seedlings in nurseries.

AWD minimises water waste by tailoring irrigation based on soil moisture.  SRI, through wider plant spacing, promotes better root development and reduces water requirements compared to traditional dense planting. Raising seedlings in nurseries allows for controlled water application and efficient use compared to direct seeding in the field. Additionally, organic supplements like  Jeevamrutham and neem cake can improve soil health, potentially leading to enhanced water retention capacity. Crop rotation with cowpea and Dhaincha can contribute to nitrogen fixation in the soil, potentially reducing the need for nitrogen-based fertilisers and indirectly promoting water conservation.

This study identified several potential responses to address reduced rainfall and water availability in Kollengode, including advanced irrigation technologies, rainwater harvesting, soil moisture management practices (mulching, cover cropping), and potentially drought-resistant rice varieties. However, further research is crucial to prioritise and optimise their implementation for local conditions. For instance, a deeper understanding of existing rice varieties and market demands for drought-resistant options is necessary before recommending a shift in cultivars. Additionally, research into the feasibility and economic viability of advanced irrigation technologies tailored to Kollengode’s specific needs would be valuable.

Detailed paper publication titled "Impact of Climate Fluctuations on Paddy Yield : A Case Study in Kollengode Village, India" with references.