Effect of Soil Types on Phenology and Heat Units of Quinoa

Quinoa (Chenopodium quinoa Willd.) is an herbaceous annual crop originated from Andean regions of South America. It is primarily grown in Bolivia and Peru and are major producers and exporters of quinoa in the world. It has earned a lot of attention worldwide owing to its unique nutritional and health benefits and its potential to adapt to contrasting environments, such as nutrient-poor, saline and sodic soils and drought stressed marginal agro ecosystems (Hinojosa et al., 2018). Apart from high protein content, quinoa is rich in essential amino acids such as lysine, methionine and threonine; micronutrients, vitamins, phenolic compounds and minerals (Egritas et al., 2022). The antioxidant level of quinoa is five times higher than those of cereal flours and also abundant in linoleic and linolenic fatty acids. In addition to being used as food for humans, quinoa seed is also used as livestock and poultry feed. Owing to its balanced nutritional benefits, the year 2013 has been declared as an international year of quinoa by United Nations (Choudhary et al., 2020).
       
Beyond climate, soil characteristics such as soil physical and chemical properties are believed to play an important role in plant growth, influencing the availability of air, nutrients and water (Loriana et al., 2020). Crop yield and soil have a complicated relationship that depends on the physical and chemical characteristics of the soil as well as other external natural influences (Juhos et al., 2015). Soils differ in their draining, water retention capacity and nutrient solubility and availability with inevitable consequences which decides the survival and performance of many crop species.
       
Determining phenology especially for a new crop in a particular region is important to understand the behaviour of the crop. It also aids in creating reliable information to support breeding and agronomical research programmes (Zuniga et al., 2017). Calculating different heat units during the crop growth allows for the estimation of different phenological events and timing of harvest of the crop (Parthasarathi et al., 2013). Apart from that the information regarding suitability of a region for production of a particular crop and effect of heat stress on crops can also be estimated through accumulated heat units.
               
Understanding how different soil types affect the growth, development and phenology of particular crops is important and this can be studied through accumulated heat units.  Quinoa is a newly evolved pseudo cereal and had a great potential in India and hence, it is utmost important to determine attainment of phenological stages. Therefore, in this investigation, the influence of different soil types on phenological development and accumulated heat units of quinoa were evaluated. 

A pot experiment was conducted in the Department of Agronomy, Tamil Nadu Agricultural University (TNAU), Coimbatore during Kharif, 2022 season. Eight different soils were collected from different areas around Coimbatore district which was laid out in completely randomized design with three replications. The places from where the soils collected were mentioned below as treatments.
T₁ - Clay loam soils of wetlands of TNAU.
T₂ - Sandy loam soils of eastern block of TNAU.
T₃ - Sandy loam soils of Mettupalayam.
T₄ - Sandy clay loam soils of 36 B eastern block of TNAU.
T₅ - Sandy clay loam soils of 37 B eastern block of TNAU.
T₆ - Clay loam soils of Ooty.
T₇ - Sandy clay loam soils of Govindanaickenpalayam.
T₈ - Sandy clay loam soils of Annur.
       
The soils used in the trail were collected from eight different representative locations at a depth of 50 cm layer of the fields. Before the start of the trail, each soil sample was sieved through 2mm sieve and were taken to laboratory for physical and chemical analysis (Table 1). The pots were filled with 6 kg of air dry soil and arranged randomly during the investigation. Each pot was sown with 20 seeds of quinoa and covered with thin layer of soil. At 5-6 leaf stage, the seedlings of quinoa were thinned in order to reduce competition. To evaluate the true effect of various soil types on quinoa production, no fertilizers were added to the pots. Water was given as required for proper germination and crop growth. Crop phenology (branching, panicle initiation, flowering and harvest stage) of quinoa was recorded as per the stage development descriptions of Zuniga et al., (2017). During the crop season, the daily data on prevailed temperature and bright sunshine hours were collected from Agro-climatic Research Centre, TNAU, Coimbatore. The details of the day length were obtained from Rastriya Panchang (Anonymous, 2022-23) published by Positional Astronomy Centre, IMD, Kolkata. The heat units were calculated as follows:
 
                                                  (Iwata, 1984)

                                                               (Rajput, 1980)

                                                     (Major et al., 1975)

                                                 ( Rajput, 1980)
 
Where,
GDD - Growing degree days.
HTU - Helio thermal units.
PTU - Photo thermal units.
RTD - Relative temperature disparity.
Tmax - Maximum temperature (°C).
Tmin - Minimum temperature (°C).
Tb -  Base temperature = 3(°C).
BSSH - Bright sunshine hours.


       
The collected data were subjected to statistical analysis and correlation was worked out between heat units and grain yield of quinoa as suggested by Gomez and Gomez (2010).

Soil characteristics
 
The physical and chemical properties of soils were analyzed in the laboratory and the results have been given in Table 1. Soils collected from eastern block of TNAU and Mettupalayam were sandy loam in texture whereas, clay loam texture was observed in wetlands of TNAU and Ooty soils. The texture of the soils gathered from 36 B eastern block of TNAU, 37 B eastern block of TNAU, Govindana ickenpalayam and Annur were sandy clay loam. Except Ooty soils, which are acidic in character (4.90), the pH of the soils varies from slightly alkaline to moderately alkaline (7.91-8.79) in all other soils. The soils used in this trail had electrical conductivity (EC) ranging from 0.17-0.96 dSm^-1, which are considered to be non-saline in nature. The clay loam textured Ooty soils registered the highest amount of organic carbon whereas, it is medium and low in soils collected from Govindanaickenpalayam, Annur and 36 B eastern block of TNAU. The rest of soils had low organic carbon content. All the collected soils have low available nitrogen content (<280 kg ha^-1), with the exception of the clay loam soils in Ooty, which have a moderate amount of available nitrogen (376 kg ha^-1). The Ooty soils had high levels of available phosphorus, whereas the other soils had medium levels of available phosphorus. All the soils used in this trail are rich in available potassium. The results of the laboratory analysis indicated that the clay loam textured Ooty soils are highly fertile over other soils. This might be due low fractions of sand and appropriate amount of silt and clay with balanced nutrient levels. These findings are in line with the findings of Shanmugasundaram and Savithri (2000). The lowest soil fertility was recorded in sandy loam soils of Mettupalayam could be due unbalanced sand, silt and clay fractions with low concentration of nutrients.
 
 
Phenophases development
 
Soils collected from different areas had shown significant impact on days required to attain phenophases of quinoa (Table 2). Among eight different soils tested, clay loam textured Ooty soils required the maximum number of days to attain different developmental stages (branching, panicle initiation, flowering and physiological maturity) of quinoa. The delay in each developmental stage of quinoa in clay loam soils of Ooty was mainly due to higher fractions of clay and organic carbon content that could facilitate greater uptake and assimilation of available nutrients which promotes the vegetative growth and also favours delayed leaf senescence, sustained leaf photosynthesis during grain filling period and had a direct impact on phenology of the crop. Ahmad et al., (2008) reported that availability of nutrients with good soil conditions promotes the duration of wheat crop. Delay in physiological maturity of quinoa was observed with increase in nitrogen levels from 0 to 125 kg N ha^-1 (Basra et al., 2014). Sandy loam soils of Mettupalayam registered the minimum number of days to attain all developmental stages of quinoa due to poor availability of nutrients. The correlation between different developmental stages viz., branching, panicle initiation, flowering and physiological maturity and grain yield was positive and significant (0.90**, 0.94**, 0.89** and 0.93**, respectively) and indicates delay in attaining different phenophases favours the grain yield of quinoa.


 
Growing degree days
 
Growing degree days (GDD) required to complete each phenophase of quinoa varied in different soil types (Table 3). The clay loam textured Ooty soils required higher GDD to attain different developmental stages of quinoa when compared to other soils tried. This was mainly due to favourable soil texture with balanced nutrients that leads to a longer period for all phenological stages in turn increased the accumulated growing degree days of quinoa. Rathore et al., (2019) recorded higher GDD with longer growing period of quinoa. Sandy loam soils of Mettupalayam took the least GDD to complete each phenophase of quinoa due to shorter maturity period. Correlation between GDD and grain yield showed positive and significant relation (0.92**) which indicated that GDD had positive influence on yield of quinoa.
 

 
Helio thermal units
 
The amount of helio thermal units (HTU) to attain individual phenological stages of quinoa varied with different soil types (Table 4). Helio thermal units required to attain all the developmental stages of quinoa were higher in clay loam textured Ooty soils over other soils. This might be due to more time taken for attaining phenological stages under Ooty soils which accumulated maximum growing degree days and sunshine hours in turn increased the helio thermal units. Sikder (2009) reported highest helio thermal units with wheat cultivars of more duration. The lowest heat units (HTU) were noticed with sandy loam soils of Mettupalayam. A positive and significant correlation (0.94**) was found between HTU and grain yield of quinoa indicates increased HTU was favouring the quinoa yield.
 

 
Photo thermal units
 
Heat units in terms of photo thermal units (PTU) to pass each developmental stage varied under diverse soil types (Table 5). Among the different soils tried, the Ooty soils with clay loam in texture registered higher heat units (PTU) to attain different developmental stages of quinoa than all other type of soils under testing. Days required to attain the phenological stages of quinoa were higher under Ooty soils and also higher growing degree days directly influenced the PTU values. The least photo thermal units were observed in sandy loam soils of Mettupalayam. Correlation between PTU and grain yield was positive and significant (0.92**) and indicated a positive relationship.
 

 
Relative temperature disparity
 
With different soil types, there was a variation in relative temperature disparity (RTD) at all the developmental phases of quinoa (Table 6). Clay loam soils collected from Ooty recorded more relative temperature disparity at all phenological phases of quinoa when compared with that of other soils. As the RTD values depend on maximum and minimum temperature experienced during phenophases, the crop grown on Ooty soils took more days to pass individual phenophase, accumulated more RTD values. Thavaprakaash et al., (2007) recorded higher RTD values with late Rabi sown baby corn crop with more duration. Sandy loam soils of Mettupalayam recorded the lowest values of RTD values at all developmental phases of quinoa. The correlation was worked out between RTD and grain yield of quinoa and it was positive and highly significant (0.92**) which indicated a positive association.
 

The present investigation concludes that there was a significant effect on phenology and heat units (GDD, HTU, PTU and RTD) of quinoa due to different soils types. More number of days to attain each developmental stages and higher values of heat units of quinoa was recorded with the clay loam textured Ooty soils over other soils tested. The least days to attain different phenological phases and lower values of heat units of quinoa were recorded with sandy loam soils of Mettupalayam. The correlation between phenophases and yield indicated positive relationship. The study revealed that the soil characteristics and fertility status of the soil had strong impact on phenology and heat units of quinoa.

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