بررسی و تحلیل اقلیم کشاورزی برنج در شهرستان لنجان

The Study of Rice Agroclimatology in Lenjan

Introduction
Today, agroclimatology is one of the major trends in hydrology and meteorology, which has a crucial role in fulfilling the food requirements of different communities. The production of agricultural products is strongly correlated with precipitation and agreeable weather conditions each year. Many crops are traditionally grown in areas with harsh climatic conditions, which result in low yields and the lack of optimal exploitation of climate production capacities. One basic way to develop and promote agricultural activities in the country is to cultivate lands according to the ecological conditions. A perquisite of such development is to recognize the wide range of associated factors, including climatic and land factors. Rice cultivation, as an ecological and economic phenomenon as well as a behavioral pattern originating from human-environment interaction, is at the mercy of environmental conditions, especially climate, water and soil resources, and natural factors play a pivotal role in providing favorable conditions for rice cultivation. Identifying suitable areas for growing crops and favorable climatic and topographic conditions can improve crop production. Lenjan county, situated in a semi-arid region, has severe temperature daily, seasonal and annual fluctuations, which have worked to the detriment of various activities, especially agriculture in this city. The Zayandehrud river running through the city has laid the ground for the development of agriculture and animal husbandry. Given the huge agricultural and horticultural potentials of this county, further analysis and planning are warranted. In this research, attempts have been made to investigate the agroclimatology of Lenjan county for rice cultivation.
Methodology
Lenjan county is located 35 km southwest of Isfahan in the Zayandehrud valley. The meteorological stations studied here include Isfahan, Lenjan, Daran, Natanz and Najafabad. The data were obtained from the Meteorological Organization and the General Directorate of Agricultural Jihad in Isfahan and Charmahal Bakhtiari provinces. In this study, the daily and monthly meteorological data related to the parameters of temperature, precipitation, and relative humidity derived from these stations over a 15-year statistical period (1996-2012) were used. Then, the correlation between climatic elements and rice yield in selected stations was analyzed. Finally, after preparing climatic maps, altitude and slope levels were drawn using the Kriging method. Also, in the GIS, the final zoning map of areas suitable/unsuitable for rice cultivation was drawn according to relevant elements.
Discussion and Results
Parameters and indices of rice agroclimatology in the west of Isfahan province, which are of paramount importance in the growing season and different stages of growing rice, were studied and analyzed. The growth degree day of the rice for the whole growing period is 1500 degree day. Hence, in light of the values obtained from the active temperatures, it was observed that all stations were effective in terms of growth day degree and have favorable conditions concerning active growth day degree. The minimum critical temperature of rice is -1 °C, and in none of the stations, the mean temperature during the growing period was lower than 0 °C. The maximum days this temperature was below 10 °C during the statistical period was reported at Najafabad station, but this temperature was never recorded at Isfahan station. All stations experience weak frosts until the end of April, which in high-elevation lasts until the last ten days of May. Mild frost is also reported only at stations above 2000-m elevation and in April. Severe frost also recorded only at very high-elevation stations (altitude above 2250 m) and in the first half of April. The minimum water consumption of rice from cultivation to maturity is not sufficient in any of the stations studied. Hence, all stations must be irrigated throughout the growing season (from planting to maturity). The germination date was May 10 at Daran and Lenjan stations, June 5-10 at Isfahan station, and June 20 at Najafabad and Natanz stations. Tillering date was also from July 5 to 15 at Lenjan and Daran stations, from July 24 to 15 at Isfahan, and from August 10-20 at Najafabad and Natanz stations. This period lasts for 20 days at Lenjan station. The growth period of rice at Lenjan station was 22 days. The flowering date was from August 20 to September 10 at Lenjan and Daran stations, from September 1 to 15 at Isfahan station, and from September 25 to October 5 at Najafabad stations. At Lenjan station, the flowering period lasted for 30 days. The maturity of rice grains was from October 5 to 20 at Lenjan and Daran stations, from September 28 to October 15 at Isfahan, and from October 21 to November 7 at Najafabad and Natanz stations. The length of maturity period at Lenjan station is 15 days
Finally, after designing climate maps, altitudes and slopes were drawn by GIS and the final map of areas suitable for rice cultivation was designed according to relevant elements. The best areas were mostly located in the central and eastern parts, which overlapped with the plains. Moreover, an area of 294 square kilometers covered stretches that were not suitable for rice growth, particularly regions in the highlands of the west and north of the map, where the rainfall is lower than in other areas. These expanses are primarily located in the highlands and the vicinity of the highlands consisting of rocky and sloping lands. Infertile expanses, covering an area of 45 square kilometers, include mountains and areas bereft of agricultural soil.
Conclusion
The results of this study show that in the west of Isfahan province, there is a fertile expanse in an area of 492 square kilometers, which sits on the central areas and alluvial plains. Lenjan county is located in this area, where the late frost in spring and the early autumn cause the minimum damage.
The initial growth of roots and stems and the rise of clusters are fairly quick, but adequate water could not be supplied by rainfall. Fertile zones cover the bulk of the map, which is an area of about 738 square kilometers. l.