Modeling the dependence of the crop calendar for rain-fed rice on precipitation in Northeast Thailand

Abstract

Rain-fed lowlands are major agricultural ecosystems used for rice production in Northeast Thailand. Developing a tool to assess the effects of variable water conditions on the regional scale yield is also important to predict the effects of climate change on food supply. To estimate regional yields, we need a simple but accurate measure of the crop calendar (i.e., the distribution of planting dates), which has a strong influence on grain yield. In this article, we modeled the dependence of the crop calendar on rainfall patterns based on a survey of the region's farmers as a part of an effort to provide a stronger basis for regional yield estimates. Our survey, conducted in 11 provinces for 2 years, confirmed the existence of large windows for sowing and transplanting versus narrow windows for heading and harvesting for rain-fed lowland rice culture in all the provinces. Variable water, soil, and toposequential conditions in the paddy fields were responsible for the large sowing and transplanting windows, whereas the use of photoperiod-sensitive varieties explained the narrow windows for heading and harvesting. The crop calendar was well expressed as a function of cumulative precipitation from June onward. When the crop calendar model was combined with a simple phenologybased model that uses growing degree-days adjusted by a day-length factor, we could estimate the rice crop calendar under rain-fed lowland conditions with acceptable accuracy. The model described in this article will be combined with a crop growth model to improve regional yield estimates for rain-fed lowland rice.

Early Warning Techniques for Local Climate Resilience: Smallholder Rice in Lao PDR

“…In rain-fed production systems, insufficient early rainfall can force farmers to delay planting. Although data in Lao PDR are not available, Sawano et al (2008) studied the relationship between rainfall and planting dates in rain-fed areas of northeast Thailand, an area that is geographically similar to the central plains of Lao PDR. The authors concluded that, depending on field-level water availability from rainfall, planting dates were locally distributed over an approximately two-month period, while local harvesting took place around the same time everywhere.…”

Effects of nitrogen input and climate trends on provincial rice yields in China between 1961 and 2003: quantitative evaluation using a crop model

“…Planting time also varies from field-to-field within each region. Frequency distribution of transplanting time within a target area is an effective means to improve model performance for regional-scale yield estimation (Stehfest et al 2007;Sawano et al 2008). Previously, we expressed a frequency distribution of planting time as a function of precipitation for the rain-fed lowland production system , but in the present study, because irrigated lowland is the most common system, we assumed a fixed normal distribution in each province with the initial and terminal dates given in Yan et al (2003).…”

“…Various types of crop phenology models have been developed and used in rice growth models (reviewed by Zhang and Tao 2013), but those used for a wide range of environmental conditions generally include functions of temperature and day length to account for photoperiod and temperature sensitivities Yin et al 1997;Sawano et al 2008). In these models, parameters are specific to each cultivar estimated from controlled-environment or field experiments.…”

Estimation of water saturated areas in Northeast Thailand using a large-scale water balance model

“…Previous research on rice cultivation in Northeast Thailand reported that the timing of rice planting is highly dependent on the moisture condition of paddy surfaces, and that planting must be finished by the end of August to ensure that the plants do not reach the heading stage while immature (e.g., Sawano et al, 2008). Our results are consistent with those previous findings, and they suggest that the variability of the area of rice planted can be evaluated appropriately from the moisture condition of the land surface as estimated by our model.…”

“…Most rice in Northeast Thailand is cultivated in rainfed lowland paddies that are not serviced by water management systems. In the rainfed lowland ecosystem, surface water conditions are very dependent on climatic conditions; therefore, rice production is vulnerable to climate variability, and especially variability in precipitation (e.g., Sawano et al, 2008;Goto et al, 2008). Therefore, it is important to clarify the practical relationships between rice productivity and climatic condition in this region concretely, in order to contribute sustainable food supply under the fluctuating climatic condition in Southeast Asia.…”