The productivity of agrocoenosis in the steppe zone of Khakasia according to Terra Modis

. The article presents the results of a quantitative assessment of the productivity of agrocoenosis according to Terra MODIS within the steppe zone of Khakasia. The gross primary production of various agrocoenosis during the growing season ranges from 3.42 to 7.41 kg/m 2 . On average, the integral productivity for the growing season of 2018 was for wheat – 5.01 ± 1.04 kg / m 2 , oats – 4.86 ± 1.12 kg / m 2 , barley – 4.52 ± 0.42 kg / m 2 , buckwheat – 5.25 kg / m 2 , hayfields – 4.86 ± 0.45 kg / m 2 , deposits – 4.39 ± 0.40 kg / m 2 . Least of all phytomass were some arable fields and low-yielding crops of wheat and abandoned lands, and most of all perennial grasses and high-yielding wheat and oats. The GPP indicators are associated with the sum of positive temperatures positively (R 2 =0.673), to a lesser extent (R 2 =0.333) with a hydrothermal coefficient for the examined agrocoenosis. The most productive crops and fertile territories were determined based on the seasonal and long-term dynamics of gross productivity. An increase in productivity for some agrocenoses was noted in 2018 аccording to satellite data.


Introduction
Khakasia belongs to territories with an unstable structure of agricultural land using due to the influence of natural and anthropogenic factors, in particular the subarid climate, decreased fertility, salinization, and soil erosion and grazing. The Beisk coal deposit is located in the study area, and the coal industry is developing intensively [1]. A regular monitoring of agrocoenosis is necessary under these conditions. Remote sensing tools can significantly simplify the task of assessing the state of various plant communities throughout the growing season by ground surveys replacing or optimizing [2,3].
The purpose of the study was to evaluate the productivity of agrocoenosis on test plots in the Beya district of Khakasia based on Terra Modis satellite data.

Methods
The object of the study was the soil and vegetation cover of the arable land of the hilly steppe of the Beya region of Khakasia, used for crops (agrocoenosis), hayfields -preserved arable land (fallow) and not used fallow. Agricultural land was located in the complex landscapes of a hilly plain, where moisture is redistributed due to a surface effluent, which is associated with the development of erosion processes.
The work was based on MODIS data (https://lpdaacsvc.cr.usgs.gov/appeears): 1) MOD17A2H (gross primary productivity, kg / m 2 ) [4]; 2) MOD16A2 (evapotranspiration)  [5]. Gross productivity for the season was determined by integrating the GPP curve for the period from May 1 to August 31. Weather data provided by the site https://rp5.ru/. For regression, the calculation of the sum of positive temperatures was carried out for the period preceding the date of the survey: the sum of temperatures above 0 ° C was calculated 8 times a day (the sum of temperatures above standard). This method showed higher correlation values on the data sample.
A general route study and the establishment of decoding features of soils in satellite images were carried out. According to the main sections (depth 1.5 m), with precise reference to the terrain by GPS-navigator and digging (0.8-0.5 m), the genetic nomenclature of soils (types, subtypes, genera, species, varieties) was specified according to the classification [6]. Soil samples were taken from the genetic horizons of the soil profile for laboratory analysis and subsequent clarification of the diagnosis.
Test sites were located in the Beya vicinity (Beya district, Khakasia) on ordinary chernozems of different genera (calcareous, solonetzic, solonchakous), meadow-chernozem soils (solonchakous), as well as leached chernozems on the slopes of northern exposures adjacent to the forest-steppe (Fig. 1 The ones are the most fertile soils, both throughout the territory of Khakasia and on the site. Red-colored heavy loams and clays dominate among parent rocks in the study area. Leached chernozems are developed on eluvial-deluvial yellow-brown loams.
Geobotanical studies of fallows are observed in 2018 at test sites using the stationary area method [7,8]. The productivity of agrocoenosis was determined by the standard method. Herbage was cut off at the surface of the soil on sites 1 × 1 m 2 in fivefold repetition. The phytomass of the fallows was divided into botanical and economic groupssedges, cereals, legumes, wormwood, different herbs, rags with mort-mass. The phytomass of agrocoenosis was divided into groups -the mass of ears, vegetative mass, the mass of weeds, dry grass and mortmass. Plants were weighed in a wet and air-dry state with an accuracy of 0.01 g. Data were transferred in kg / m 2 [8,9].
Statistical analysis (regression, calculation of the confidence interval, arithmetic mean and standard deviation) was performed in Microsoft Excel.

Results
The total productivity of gross productivity for the growing season of 2018 was calculated according to Terra MODIS ( Table 1).
As can be seen from table 1, the most minimal value of the indicator for wheat crops (20k) was 3.57 kg / m 2 on meadow chernozem solonchakous, with a sulphate-soda type of salinization. The limiting yield factor in this case, obviously, is salinization, especially soda -the most toxic for most plants.
On average, the integral wheat productivity for the growing season (2018) was 5.01 ± 1.04 kg / m 2 . For comparison, we present the phytomass of wheat sowing (11 k) in the second decade of August. The phytomass of ears was 0.091 kg / m 2 in raw form (0.061 kg / m 2 in dry), the vegetative mass was 0.084 (0.060) kg / m 2 , weeds 0.231 (0.074) kg / m 2 , dry grass and mortmass 0.183 (0.107) kg / m 2 .
During this period, the productivity of this agrocoenosis based on MODIS data was 0.0262 kg / m 2 , aboveground phytomass was significantly higher -0.589 kg / m 2 in raw form and 0.302 in dry form. The differences are explained by the phenological state of wheat and the presence of a significant amount of dry grass, which reduces the value of the indicator.
Similar indicators were observed for barley (4.22 and 4.82 kg / m 2 ) and oats (4.06 and 5.65 kg / m 2 ). Ground-based studies have shown high grain yields in the contours: 4T, 5T, 9T and 10T. It is associated with increased moisture capacity of the heavy loamy ordinary and leached chernozems, as well as average indicators of their potential and effective fertility (humus content 4.5-5.6%, mobile phosphorus and potassium, respectively 20.5-23.9 and 214-276 mg / kg of soil). A high yield was noted according to ground data in the contours of 9T and 10T, which is associated with high fertility.
The barley was more productive than the wheat in accordance with ground-based data. Hayfields had values close to wheat; their projective cover did not exceed 50%. The most productive were perennial grasses of the fourth year of use -Elytrigia repens + Onobrychis arenaria and Melilotus (7.41 and 5.14 kg / m 2 ). 4.26 1643 0.508 0.279 1 -gross primary productivity, kg / m 2 ; 2 -evapotranspiration, kg / m 2 ; 3 -coefficient of determination of the polynomial equation of the third degree of GPP correlation with the sum of temperatures; 4 -same for GPP with hydrothermal coefficient; 5 -cereal (wheat) was subsequently planted on these arable fields.
During the season, the phytomass of agrocoenosis intensively increased at the end of May, and then the development maximum remained until the beginning of June (Fig. 2). Further, the mass decreased except for two peaks in early July and August, associated with favorable weather conditions. The main seasonal increase in GPP was in early June, the end of the first decade of July, the end of the third decades of July.
Evapotranspiration (ET) can serve as an indirect method for assessing soil moisture content, and the GPP is higher the higher the ET (Table 1). This indicator increases with significant phytomass (due to the volume of the transpiration surface of the leaves), good water availability, and partly with a decrease in projective cover. It is worth noting that the vegetation cover to some extent prevents the drying out of the soil.

Fig. 2. Seasonal productivity of individual agrocoenosis in test plots
The relationship between weather data and distance indicators allows you to determine the degree of weather sensitivity of crops. On average, for the examined agrocoenoses, the GPP indicators are associated positively with the sum of positive temperatures (R 2 = 0.673), to a lesser extent (R 2 = 0.333) with a hydrothermal coefficient.
Long-term changes of the productivity were also analized for individual agrocoenosis ( Table 2). The most productive areas were those where in 2018 were located arable fields (5 T), wheat (10 T), Elytrigia + Onobrychis, and oats (9 T). The remaining communities had

Conclusion
Thus, the gross productivity of agrocoenosis for the season in the study area was calculated and the differences between them were determined. Least of all phytomass were individual arable fields and low-yielding wheat crops (3.6 kg / m 2 ), fallows, and most of all perennial grasses and high-yielding wheat and oats (up to 5.02-7.41 kg / m 2 ).
Terra Modis data allows you to rank phytocoenosis by productivity and choose the optimal crops for growing in a particular area. Terra Modis satellite data showed a positive correlation with ground-based data and can be used for agroecological monitoring and optimization of land reclamation in the Beya region. The results obtained are of practical interest for the optimal placement of crops and agricultural cultivation technologies; monitoring fertility and the state of agrocoenosis; calculation of their normative productivity.