Growth and potassium uptake by Maize ( Zea mays L . ) in three soils differing in clay contents

Soil texture affects nutrient availability in soil hence affects plant growth. Soils high in clay contents retain more K, and generally plants grown on these soils do not respond to applied K. A pot experiment was conducted to evaluate growth response and Kuptake by maize plants grown on three different textured soils. There were four K levels 0, 50, 100 and 150 mg K/kg soil. Ten seeds of hybrid maize (cv. Magic) were sown in each pot which was replicated four times. Crop was harvested after seven weeks. Root and shoot dry matter was recorded and samples were analysed for K concentration. Soil texture significantly (p< 0.05) affected biomass production by maize plants. Shoot dry matter produced was maximum in plants grown in sandy soil. Root growth was minimum in soil high in clay contents compared to plant grown in sandy soil. Root to shoot dry matter ratio correlated negatively with clay contents (r = 0.91) showing limited root growth in soils high in clay contents. It also influenced total dry matter (TDM) as indicated by its positive correlation (r = 0.83). Potassium application did not affected plant growth in soil high in clay content, however, K uptake was increased with an increase in Klevel in soils low in clay contents. Total dry matter was significantly correlated (r = 0.83) with root Kuptake, but correlation with shoot Kuptake was not significant.


Introduction
A number of soil properties are influenced by soil texture particularly nutrient availability and in turn it affects plant growth (Tagar and Bhatti, 1996).Soils rich in clays and organic matter contents hold more nutrients than sandy soils (Brady, 1974).Potassium (K + ) is an important macronutrient and is elusive in the soil with respect to plant availability.Most of its elusiveness is the consequence of the amount and type of clay minerals present in the soil (Ranjha, 1988).Furthermore, low hydration energy of K + ion favours its entrapment in lattice voids of the micaceous structure (Maclean, 1978).Joshi et al. (1978), while working on K + fixation and forms in Jodpur soils of India, noted significant correlation of clay contents with K + -fixing capacity of soil.Clay minerals have the capacity to reduce plant available K + through K + -fixation (Blake et al., 1999).In alluvial soils, quartz and feldspar largely constitute the coarse fraction, where as finer particles mainly contain micas and illitic minerals which are much rich in K + (Kanwar, 1961).When the concentrations of soil solution K + and /or exchangeable K + depleted due to uptake by plants and leaching, interlayer K + releases to fulfil demands of growing plants (Hinsiger and Jaillard, 1993).Fine textured soils hold more potassium than coarse textured soils (Eldamaty et al., 1963), hence crops response to applied K + varies from soil to soil.The study was conducted to evaluate the effect of soil texture and K + application on biomass production and K + uptake by maize plants.

Materials and Methods
The experiment was conducted in a wirehouse at University of Agriculture Faisalabad, Pakistan, where mean temperature was 35°C and 18°C at day and night respectively during the whole growth period.Three soils dominant in Mica clay minerals and differing in texture (S 1 , S 2 and S 3 ) were used in this experiment and characteristics of these soils are presented in Table 1.The soils were air dried and grounded in a mechanical grinder to pass through a 2 mm sieve after mixing it thoroughly.The prepared soil was filled in earthen pots at rate of 11 kg soil per pot.The pots were earlier lined with polyethylene sheets.Four levels of K + viz, 0, 50, 100 and 150 mg K + per kg of soil along with N and P at rates of 150 mg N per kg and 100 mg P per kg of soil, were added to respective pots and mixed thoroughly.A randomised complete block design was employed with three replications.Pots were irrigated with distilled water to get optimum moisture level for seed sowing.After 5 days of fertiliser addition, ten seeds of hybrid maize (cv.Magic) were sown in each pot.Plants were thinned after a week of germination to maintain five plants per pot.Plants were harvested after seven weeks of germination and washed with distilled water to remove any dust particles.Washed samples were oven dried at 80°C for 48 hours to record their oven dry weight.Dried samples of shoots and roots were grounded in a mechanical grinder to pass 40 mesh and were digested in diacid mixture of perchloric and nitric acid (3:1) (Miller, 1998).Sample digest were analysed for K + concentration to calculate K + uptake by roots and shoots separately.The data was statistically analysed following the method of Steel and Torrie (1980).

Biomass production
Soil texture affects plant growth by influencing soil aeration, root penetration, water holding capacity and nutrient availability in soil ( Tagar and Bhatti, 1996 ).Data regarding shoot dry matter (SDM), root dry matter (RDM), total dry matter (TDM) and root shoot ratio (RSR) of maize plants grown in three soils (Table 2) revealed significant effect of soil texture on all of these parameters.Shoot dry matter production is a good indicator of economic yield hence is considered as suitable parameter to study growth response of plants at seedling stage.SDM production by maize plants was increased in S 1 and S 2 when K + levels were increased although increase was non-significant.However, K + application did not affected SDM in S 3 having maximum clay contents (37 %).Soils high in clay contents generally are rich in available K + and have more K + fixing capacity hence, crops grown on these do not respond to applied K + as in our study.Shoot dry matter production was higher in S 3 when no K + was applied, but it was higher in S 1 and S 2 when averaged over all K + levels.Soil texture affects root growth by affecting aeration, moisture and density of soil.Root growth is maximum in soils high in sand percentage (S 3 ) as roots have to explore more volume in search of nutrients and ease of growth.In this study RDM negatively correlated (r = 0.85, p> 0.05) with clay contents and was significantly higher in S 1 compared to S 2 and S 3 .However, K + application did not affected root growth by maize plants significantly in all of these soils.Particle size distribution in soils affected biomass partitioning between shoots and roots as exhibited by higher RSR values in S 1 .However, K + application did not affected RSR in all of these soils.Root shoot ratio was correlated negatively with clay contents (r = 0.91) showing limited root growth in soils high in clay contents.McKenzie et al. (2001) also observed limited root growth in soils high clay contents due to more strength.RSR influenced TDM as indicated by positive correlation (r = 0.83) that plants with higher RSR produced maximum TDM.Total dry matter was also higher in S 1 compared to S 2 and S 3 and it was attributed to increased growth of roots in S 1 .

Potassium concentration
Shoot K + concentration and uptake was significantly increased due to K + application in S 1 , while effect was non-significant in S 2 and S 3 .Plants grown in different soils varied significantly for shoot and root K + concentration and uptake (Table 3).Potassium concentration and uptake by shoots of plants grown in S 1 was lower compared to plants grown in S 2 and S 3 .Higher K + concentration in plants grown with S 2 and S 3 indicated that K + availability was not the limiting factor for reduced shoot growth.But these were higher clay contents which affect plant growth as exhibited by highly significant negative correlation (r = 0.85) between total dry matter and clay contents.
Root K + concentration and uptake was significantly higher in plants grown in S 1 at all levels of K + supply.Due to low clay contents in S 1 , root growth was maximum which significantly increased K + uptake by roots.
Total dry matter was significantly correlated with root K + uptake (r = 0.83), (Table 4, Figure 1 & 2) but correlation with shoot K + uptake was non-significant.Potassium application increased shoot and root K + uptake in S 1 and in S 2 where as increase was non significant in S 3 .Total K + uptake by plants increased as K + levels was increased from 0 to 150 mg/kg of soil, in soils low in clay contents (S 1 and S 2 ) and was attributed to maximum shoot and root biomass produced in S 1 and S 2 compared to S 3 .

FF
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