Perspectives for cultivation of diversified crops in a rice (Oryza sativa L.)-based crop rotation in the Kyzylorda region, Kazakhstan

In the Aral Sea basin of Kyzylorda region, Kazakhstan, rice (Oryza sativa L.) is a main crop and annually occupies more than 45% of the total area of agricultural crops. However, about 90% of Syr Daria River waters is consumed for agricultural purposes, mainly for irrigation of paddy fields. In addition, there is an annual variability in the volume of water during the growing season, which creates certain threats to ensuring guaranteed water supply to irrigated lands and may pose a desertification risks. In addition, in the studied region, due to insufficient application of phosphorus fertilizers nutrient imbalance has been observed in the soil. The aim of the research was to develop sustainable production of rice by introduction of diversified cultures such as barley, soybean and rapeseed: Hordeum vulgare (L.), Glycine max (L.) and Brassica napus (L.), respectively, in a ricebased crop rotation and application of the different doses of mineral fertilizers in the Kyzylorda region. The results of the study showed that application of phosphorus as the main fertilizer at a dose of 90 kg ha-1 gives a significant increase in yield. Studied barley and rapeseed crops showed better adaptability to the specific agroecological conditions. These crops are recommended to be introduced into the rice crop rotations in order to produce rice using environmentally friendly technology.


Introduction
Desertification in Kazakhstan affects the country's environment, agriculture and animal husbandry.
Due to the arid climate, water has become a priority in the socio-economic development of Aral sea region of south Kazakhstan. It is critical to quickly and accurately identify the locations of desertification land and grasp the main causes of desertification in different regions of Kazakhstan.
Land desertification is a key land degradation process that affects the ecological environment and regional sustainable development in arid and semiarid regions of the world and directly affects a global population of more than 1 billion people and 40% of the total land surface (Verón et al. 2006). In monitoring studies of the Kyzylorda region, Yunfeng Hu et al. (2020) reported that approximately 24.1 × 103 km 2 of land, which accounts for 10.5% of all Kyzylorda territory, is in a state of desertification.
In Kyzylorda region, rice (Oryza sativa L.) is the main crop and annually occupies more than 45% of the total area under crops. The importance of rice for the region as an economic, ecological, and cultural is huge, while its role as a reclamation culture is invaluable. Irrigated agriculture diversification by replacing the vacated areas with less water-consuming crops in the Kyzylorda region. It is possible through higher crop diversity in a crop rotation (Renard and Tilman 2019), mixed cropping (Bedoussac et al. 2015) cultivation of grain legumes in otherwise cereal dominated systems (Watson et al. 2017), and regionally adapted varieties or variety mixtures (Yang et al. 2019;Vijaya et al. 2019;Fita et al. 2015) as well as multiple cropping or intercropping.
Long-term cultivation of rice in the conditions of the Kyzylorda region led to a general rise in the level of groundwater in the fields where rice was cultivated, and in adjacent fields of natural agrophytocenoses where rice was not cultivated. This is exacerbated by the hot and dry climate, which causes strong evaporation of soil moisture, which intensifies salinization processes, especially when saline groundwater level is high (Funakawa et al. 2000;Kitamura et al. 2006;Funakawa and Kosaki 2007;Funakawa et al. 2007;Ibrakhmov et al. 2007;Orazkhan et al. 2016;Hamidov et al. 2016). The continuing processes of salinization of the territory are caused, on the one hand, by an increase in the salinity of irrigation water and groundwater, and, on the other hand, by insufficient drainage of the territory (Baimbetov et al. 2005).
According to scientists from the Kazakh Research Institute of Rice Cultivation, production of rice, allows reduction of soil salinity due to washing the salts downward. However, in order to obtain high rice yields and at the same time to combat desertification processes, new technologies need to be introduced adapted to the specific regional climatic and economic conditions. In the region, the active development of the livestock industry, the opening of a large feed mill and many feedlots have already created a high demand for fodder crops. Nowadays, alfalfa is actively introduced in the ricebased crop rotations. In addition, barley, wheat, millet, corn and other crops are in high demand in the region.
Cultivation of perennial grasses, mainly alfalfa, is the determining factor in maintaining and increasing soil fertility (Dedov et al. 2016;Bondarenko 2019). Many studies have shown that along with the traditional rice, crops such as barley, oats, rapeseed, sorghum, millet, soybeans, safflower may greatly contribute to a rational use of the bioclimatic potential of the region (Ray et al. 2009;Ali et al. 2012;Jat et al. 2012;Orazkhan et al. 2016;Cuevas et al. 2019;Hufnagel et al. 2020). The listed studies confirm that diversification of rice growing fields can both improve soil quality parameters and at the same time save water for irrigation. Particularly, in the semi desert of Aral Sea region where a shortage of irrigation water is highly urgent, upland crops can save water using the moisture accumulated after rice. They are able to form a high yield without a single irrigation. With a short growing season, these crops mature before the onset of the dry season and allow rational use of resources with the possibility of reusing these fields for other crops. Kui Liu et al. (2019) suggested that in changing climatic conditions, diversifying traditional rapeseed systems based on wheat or fallow using lentils and B. Junce (L.) will increase the system productivity and yield stability in different environments. Assefa et al. (2021) found that the rice-based cropping systems including diversified crops had a relatively higher income than traditional systems. In reviewing existing publications, Hamidov et al. (2016) found that there are many gaps in research knowledge regarding the agricultural land use to sustainable development in the Aral Sea basin. The hypothesis was that barley and rapeseed has a better adaptability to a specific climatic condition and therefore can be included in a rice-based crop rotation system in order to obtain organic rice production. The main goal of our research was to study effect of introduced diversified crops in three different rice-based croprotation systems and the effect of various doses of mineral fertilizers on indicators of productivity of diversified crops in the Aral Sea region, Kazakhstan.

Materials and methods
Two field experiments were studied. In the rice-based crop rotation experiments, three schemes containing alfalfa, melilot and diversification crops (barley, wheat and oat) were studied and compared (Table 1). In the fertilization experiment, the diversification crops barley (Hordeum vulgare L.), soybeans (Glycine max L.) and rapeseed (Brassica campestris L.) were studied with four different doses of N:P:K fertilizers: The object of research was domestic varieties of diversification crops: Barley -,,Asem"; soybean -,,Misula"; rapeseed-,,Jubilee". The area of each treatment (plot) was 50 m², the seeding rates were: for barley -4 million seeds per 1 ha; soybeans -85 thousand seeds per ha; rapeseed 1.2 thousand seeds per ha. Germination was determined based on the number of grains per 1 m² with the following values: barley -400 pieces; soybeans -85 pcs; rapeseed -120 pcs.
Counting of the harvest was carried out on a plot basis. Determination of the qualitative composition of grain was carried out in the analytical laboratory of the Kazakh Research Institute of Agriculture and Crop Production (Almaty): protein content by the Kjeldahl method. Approximately 1g of raw material was hydrolyzed with 15 mL concentrated sulfuric acid (H2SO4) containing two copper catalyst tablets in a heat block at 420 °C for 2 h. After cooling, H2O was added to the hydrolysates before neutralization and titration. The amount of total nitrogen in the raw materials were multiplied with both the traditional conversion factor of 6.25 (Kjeldahl 1883) and speciesspecific conversion factors (Lourenço et al. 2002) in order to determine total protein content. Starch was determined by the polarimetric method (Mineev 2001). This method includes a double polarimetric determination. In the first determination, the sample was treated with warm diluted hydrochloric acid, clarified and filtered. The optical rotation of the resulting solution was determined.
In the second determination, the sample was extracted with 40% ethanol and filtered. The filtrate was acidified with hydrochloric acid, clarified and filtered again. The optical rotation of the resulting solution was determined. From the difference of both rotation angles the content of starch was calculated. The results were statistically processed by the analysis of variance according to Dospekhov (1973).

Crop rotations schemes
Taking into account the results of our previous studies with barley (Tokhetova et al. 2017 Nurymova et al. 2020) we have developed new scientifically sound schemes of rice-based crop rotations with inclusion of diversified crops. The load of rice in a rotation was 37.5-50% (Table 1). In all three schemes, diversification crops were placed on the 1 st and 6 th fields after rice, which leaves a large supply of moisture, ensuring an even (simultaneous) shooting and respectively, the formation of an optimal stemming and total yield. Rice is a semi-aquatic plant, which requires a water-saturated environment during most of its life cycle (Qin et al. 2020) thus leaving high moisture reserves in soil. When placing crops on the post-rice fields, spring water-recharge irrigation is not carried out, since the available moisture ensures normal growth and development of plants throughout the growing season. This approach can be a part of the environmentally friendly rice-production. Table 1 shows that diversification crops (DC) in the 1 st field are sown as cover crops of alfalfa.
On the 6 th field of the 1 st and 3 rd crop rotation schemes, melilot is used as a cover crop, and on the 6 th field of the 2 nd scheme, DCs are sown. Because sorghum is a moderately salt-tolerant crop (Soni et al. 2021), after harvesting the DCs, it is possible successfully cultivate sorghum or millet as a second crop and green fodder. We suggest that this approach can contribute to a rational and effective use of lands because less irrigation will reduce secondary salinization at the same time saving water, while inclusion of DCs will facilitate maintaining soil health (Soni et al. 2021).
Long-term studies have shown that, under conditions of salinity or drought, specifically adapted varieties for local conditions show higher productivity than varieties of foreign-regional selection (Jung et al. 2020;Bohnert et al. 1995;Bray 1997;Chourey et al. 2003;Loescher et al. 2011;Goncharov and Goncharov 2009;CGIAR 2012;Pryanishnikov 2018). For example, inclusion of barley contributes to better weed control, thus being a field phytosanitary crop (Jabran 2017). At the same time, barley requires less water than wheat and rice (Khan et al. 2010) and is a more salt-tolerant crop. At the initial phase of the growing, barley grow quickly and intensively thus creating optimal conditions for the growth and development of perennial grasses on saline soils, shading them from direct sunlight (Khan et al. 2010). As a result of the short growing season, and therefore due to early harvesting of barley, the grasses released earlier from the cover crop and develop well in late summer and autumn, implying that it can be used as a cover crop in rice crop rotation too. After harvesting of the clean barley sowing, millet can be successfully cultivated, whose optimal sowing time coincides with the beginning of summer.
The role of alfalfa in a rice-based crop rotation, as a nitrogen-fixing crop, is very large, due to depositing nitrogen from air into soil in the form of protein substances. The latter, after mineralization, transforms into accessible for rice plants nitrogen (Pryanishnikov 1985;Wong 1980;Severov 2000;Posypanov 2007; Doev 2017; Chukhil 2017).
Perennial grasses leave behind a huge amount of organic residues in the form of roots, fallen leaves and stems (Alborova et al. 2012; Bondarenko 2019). When symbiotic nitrogen fixation is activated, alfalfa crops form a more powerful root system, and after harvesting, they leave about 2.9 t ha -1 of organic matter and up to 55 kg ha -1 of nitrogen in the soil. Besides, alfalfa helps to control weeds, including such malicious weed of rice fields as Phragmites australis (L.) (Doev 2017).
However, in Aral Sea region, a limiting factor in the diversification of crop production is a lack of varieties of oilseeds and legumes zoned in the Kyzylorda region. In this regard, there is a need to expand works on environmental testing of wider choice in the production of crop varieties, in order to select the most adapted to local conditions.

Fertilization experiment with inclusion of diversified crops
Germination. Of all agricultural practices, one of the leading places in increasing the productivity of agricultural crops belongs to fertilizers. For the formation of a high yield, rapeseed requires an increased supply of mineral nutrients and, in turn, responds well to their presence in soil. On saline soils of rice systems with a dry residue 1.0% and more, germination of the crops is suppressed, which entails a strong inhibition of growth processes (Paul 2012;Qin et al. 2020). Bahizire (2007) reported that the emergence of 12 canola cultivars reduced by an electrical conductivity (EC) of 8 dS m -1 .
Some previous studies showed that rice yield decreases when saturated ECe is >3.0 dS m −1 , while 50% of yield loss is expected at 6-7 dS m −1 (Maas and Hoffman 1977;Ayers and Westcot 1985;Francois and Maas 1999). Our results showed that on saline soils of rice systems, soybean plants did not show good development. In particular, their shoots appeared on the 19-21 st day after sowing (Table 2), while the phase of full ripeness lasted until mid-September, implying poor growth intensity under the given conditions. On the contrary, rapeseed seedlings appeared very quickly and amicably, already on the 12-13 th day after sowing on April 17. The branching phase took place between May 11-17. The density of plants standing of rapeseed was higher than of soybean plants (Table 2).
In the treatment without fertilization, low germination was observed for soybean that amounted to only 29.4%. For barley and rapeseed, the germination was 42.3 and 50.8 %, respectively. In comparison with other crops, application of mineral fertilizers on barley did not reveal any significant difference between the treatments. Only a slight increase by 2.3% in germination was noted on the N90P90 treatment compared with the control.
A different trend was observed for the soybean and rapeseed plants, where the application of nitrogen at a dose of 60 kg has led to a slight increase in seed germination by 9.4 and 5.0%, respectively. And the application of phosphorus at a 90 kg ha -1 dose in the treatments with nitrogen N60 and N90 resulted in a significant increase in seed germination, in particular, in the treatments with nitrogen and phosphorus at 90 kg ha -1 : for soybeans by 14.1%, for rapeseed -9.2%.
In ecologically unfavorable conditions of the Aral Sea region, the germination capacity of seeds in many respects depends on the completeness of seedlings, optimal stalk and total yield. As known, plant growth is inhibited on saline soils. One of the solution to this problem is the creation of salt-tolerant varieties of barley with the application of the optimal dose of mineral fertilizers. In our experiments, this was the treatment with N90P90, which allowed obtaining the barley plants with optimal stem size (above 60 cm), which prevents the overgrowth of grasses above the cover crop.
The results showed a high responsiveness of the rapeseed crop to the application of mineral fertilizers. In the control treatment, the rapeseed yield was only 0.87 t ha -1 , while in the fertilized treatments it reached 1.49 -1.95 t ha -1 , significantly exceeding it by 0.62 -1.08 t ha -1 , or 71.3 -
Application of phosphorus, as the main fertilizer, in a dose of 90 kg ha -1 resulted in a significant increase in the yield and other plant characteristics of all the crops studied. When comparing the 2 nd and 3 rd treatments, which are differing only in the dose of phosphorus fertilizers, a higher increase in yield was observed on barley -0.35 t ha -1 and rapeseed -0.23 t ha -1 , while for soybean, the increase amounted to 0.13 t ha -1 . This was because the soils of rice systems are very responsive to phosphorus on the studied region. There has long been an imbalance between the main types of nitrogen and phosphorus fertilizers, associated with the economic difficulties of rice-growing farms, where, phosphorus fertilizers are often not applied or are applied in insufficient quantities.
Analysis of grain quality of barley and soybeans showed that application of only N at a dose of 60 kg leads to both an increase in protein content and protein yield per hectare for both crops. A further increase in the dose of mineral fertilizers had a positive effect on the increase of protein content in barley grain and in soybean seeds. In particular, the N90P90 treatment provided a significant increase of the protein content, in comparison with the control treatment: in barley grain -14.5%, against the control variant -11.5%; in soybean seeds -23.5%, against the control -20.5%. However, although the protein content in grain of barley is almost two times inferior to soybeans, in terms of protein yield per hectare it exceeds by 0.13 tonnes, due to the higher grain yield.  In the study conducted, no significant relationship was found between the oil content in rape seeds and application of different doses of fertilizers. In the control treatment, oil content of the rape seeds was 34.0%, which after application of mineral fertilizers ranged from 34.5 to 34.8%, i.e. the difference was only 0.5 -0.8%. However, for the yield of oil from one hectare, this difference was significant, since it largely depends on the yield of seeds. The largest yield of oil was obtained on the N90P90 treatment -0.67 t ha -1 , which exceeds the control by 0.2 t ha -1 (LSD05 -0.112). Hence, it follows that the yield of oil from rapeseed seeds in our experiments largely depended on the yield of seeds, while the effect of mineral fertilizers was insignificant.

General discussion
Legumes are good precursors for other crops (Chibis and Chibis 2021) due to the inputs of fixed N, where for alfalfa, red clover, pea, soybean, cowpea, and vetch it is about 65 to 335 kg of N ha −1 year −1 (Tate 1995) or 23 to 300 kg of N ha −1 year −1 (Wani 1995 (Snowdon et al. 2006). Rapeseed also possesses a complex of such valuable qualities as a wide ecological adaptability, cold resistance, early maturity, high seed productivity, which favourably distinguishes it from many other crops (Oplinger et al. 1989;Fridrihsone et al. 2020). It can feed in early spring and extends the grazing season into the late autumn until the snow cover is established (Canola encyclopedia). In addition, rapeseed is a good predecessor crop. It contributes to a decrease in weed seed stocks by 14-22%, the prevalence of the disease by 1.5 times, the development of root rot of cereals by 4.0 times and an increase in yield up to 0.3 t ha -1 . In addition, rape stubble provides a wind-resistant field surface (Adyaev et al. 2007;Malakhov 1986;Savenkov 1997) Obtaining high and stable yields of any crop is possible only with its correct placement in the crop rotation. Currently, the farms of the Kyzylorda region have 271 rice-based crop rotations, most of which are eight-year length. They have one field for grain crops (winter wheat, spring wheat or spring barley) where they are grown as a single crop or as cover crops for perennial grasses such as alfalfa. In our proposed schemes, two fields are allocated for sowing cereal crops.

Conclusions
1. In the fallow field of rice-based crop rotation, more even shooting was observed for barley and rape compared to soybean, because soybean requires integrated protection against pests and diseases in the initial phase of ontogenesis. Since barley and rapeseed showed better adaptability to the specific agro-ecological conditions in the rice-based crop rotation, they are recommended as rice precursors for cultivation in a fallow field in order to obtain organic rice production.