Identification and conversion rate of rice field in Semarang year 2000-2019

. The development of population will be followed by efforts to fulfill facilities and infrastructure also development efforts and the impact is land conversion. Land which often get conversion is rice field, so it causes shrinkage of rice field land. This study aims to determine the extent and shrinkage rate of rice field in Semarang. The method used in this study was imagery satellitein 2000-2019 and calculated with ArcGIS 10.6.1. The results showed that in Semarang there are rice fields shrinkageabout 2,368 hectares (Ha)from 2000 to 2019 or 50,81% of shrinkage rate.


Introduction
Population growth will have an impact on fullfillness the needs of human life, some of the needs are residential, places for economic activity such as factories, shops, markets and others. Efforts to fullfill those needs are carried out by converting agricultural land, mainly from agricultural land to non-agricultural land. Conversion of agricultural land generally occurs and regrettable if the converted land is productive such as rice field.
Agricultural land conversion causes shrinkage of agricultural land which is still productive, the shrinkage of agricultural land in Java has been very massive and uncontrol.Every year more than 80 thousand hectares of agricultural land is lost and converted. It is estimated that in 2025 the area of agricultural land in Indonesia will be two million hectares left. In Central Java from 2000 to 2010was noted that there wererice fields conversion around 14,830 hectares (Ha) (1.483 Ha/year or 4.12 Ha/day) [9]. The conversion of rice fields into residential and buildings in Gunungpati sub-district, Semarang from 1994 to 2010 around 384.40 Ha [2].
Semarang is one of big city with the most development in Central Java, because it is the central of government, commerce, education, services and it is the capital of Central Java Province. The development and economy of Semarang increases and becomes an attraction of urbanization for people in suburb. The Increase of population and effortof fullfillment for community daily needs also the increase development activities certainly have potential occuranceof conversion from agricultural become non-agricultural.
Agricultural land has social, economic and environmental benefits. Socially, agricultural land is the existence farmer community, economically, the width of agricultural land is certainly related to the amount of production and income. While in terms of environment, agricultural activities is in balance with the principles of environmental preservation [4].
Agricultural land conversion has some negative impacts, such as, the reduce of productive agricultural land, the decrease of agricultural products, the decrease of job opportunities and income for farmers [8]. In addition, the conversion of agricultural land into non-agricultural land also will give bad effect to social and cultural aspects of farmer, farmer's family economy and environmental quality decrease caused by uncontrol conversion. In Semarang there was a conversion around 60.63 Ha of rice field during 2000-2009 and predicted in 2076 rice fields in Semarang would be lost [3]. The main study of agricultural land conversion includes changes pattern, spatial patterns(distribution) and conversion rate (intensity), this is certainly important to study considering agricultural land conversion in Semarang is getting out of control from year to year. The aims in this study are: a). Knowing the distribution of rice fields in 2000-2019. b). Knowing the intensity/conversion rate of agricultural land in 2000-2019.

RESEARCH METHODS
This research was conducted in the city of Semarang, especially in areas that experienced conversion of agricultural land to non-agricultural land in the form of settlements. The selection of the area is based on a map of land use change / conversion that occurred in Semarang City. The design of this research is exploratory descriptive, namely research on a condition by making descriptions and descriptions systematically, factually and accurately about the facts, the nature and studying the relationships between observed phenomena (Nazir, 2005).
The population of this study is all agricultural land in Semarang in 2000-2019. The method of collecting sample is saturated sampling, which the sample is rice fields in Semarang year 2000 and 2019.
Data analysis used is analysis of rice fieldconversy distribution and field conversion rate analysis. Partial shrinkage rate of land can be explained as follows V = (Lt-L_ (t-1)) / L_ (t-1) x 100% (1) Where: V = Land shrinkage rate (%) Lt = Land area of t-year (ha) Lt-1 = Land area of the year before t (ha)

Distribution of rice fields in Semarang period 2000-2019
Total area of rice fields in Semarang in 2000 was 4661.29 Ha, or around 12.04% of Semarang total area 37,300 Ha. Distribution of rice fields in Semarang year 2000 spread in 10 of 16 sub-districts. Mijen is asub-districtwhich has the widest rice field in 2000 with 1228.72 Ha or 3.29% of Semarang total area, while the sub-districtwhich has the narrowest/smallest rice field is Gayamsari with 72.62 Ha or 0.19% of Semarang total area.

Conversion Rate of Rice Fields in Semarang period 2000-2019.
Rice fields from 2000 to 2019 in the most sub-districts in Semarang get significant conversion, the effect is rice fields area in Semarang has decreased.  From Figure 4, it is known that Gunungpati is a sub-districtwhich has the most shrinkagearea of ricefield from 2000 to 2019 which is 767.67 Ha or the same as 40.4 Ha/Year. The shrinkage areacaused by agricultural land conversion in Gunungpati subdistrict is due to Gunungpati area become the central of education and residential. That city developments, lands in Gunungpati sub-district is convertedfrom agricultural land becomes non-agricultural land or becomes residential and other buildings [2]. Semarang Mayor Regulation No. 16 year 2012 concerning on Regional Development Work Plan (RKPD) states that Gunungpati Sub-districtis include in BWK VIII (Urban Area Dividing Plan) where the main function of that development area is for educational development.  SEMARANG TIMUR  SEMARANG TENGAH  SEMARANG SELATAN  GAJAHMUNGKUR  CANDISARI  GAYAMSARI  SEMARANG BARAT  GENUK  NGALIYAN  BANYUMANIK  TUGU  PEDURUNGAN  TEMBALANG  MIJEN  GUNUNGPATI In its development Gunungpati sub-district became a magnet for economic development because there are development of educational facilities, the community change the function of rice fields into business place such as restaurants, boarding houses and residentials. From Figure 5. it is known that Banyumanik sub-district has the highest conversion rate of agricultural land it is 71.30%. In 2000, there were 166.02 hectares of rice fields and in 2019, there were many functions and 47.64 hectares rice fields left. High conversion rate in Banyumanik sub-district occurs because narrow agricultural land is not comparable to the very high demand of land. With total area 4,8000,688 Ha, and population density 6.421 people/Km2 [1]. Banyumanik sub-district is a residential area and as a trade center. Geographically, Banyumanik sub-district is a strategic hilly area, there are many residentials and trade centers, in addition it is also an office area, especially military offices, there is high way access and supermarkets and shopping centers make the land prices is costly. This is encourages farmers or rice field owners to sell or convert the agricultural land to non-agricultural land. That due to big insistence of non-agricultural sector, under the pretext of development, the owner of land become weak party with low bargaining position so the agricultural land certainly convert, to other hand if farmers do not sell their agricultural land, but in their surrounding area has been sold and already built it will certainly be a problem in cultivating land due to the cut off irrigation channels [3]. The phenomenon of agricultural land conversion rate in Semarang will certainly affect to the efforts to realize sustainable agriculture, especially the three sub-districts that getwide land conversion, namely, Gunungpati, Mijen and Tembalangare areas intended for food crop agriculture [5]. The highshrinkage of agricultural land area and the rate of agricultural conversion land will certainly reduce productivity value of agricultural product, so government's efforts to realize food sustainable and independence in Indonesia will be more difficult to realized [7].