Response of Lentil (Lens culinaris Medik.) to Potassium Application under Deficient Soils

Location and treatment details
 
The experiment was carried out at the research farm of Punjab Agricultural University Regional Research Station, Gurdaspur situated at 32° 03' N and 75° 25' E. The soil was classified as fine loamy, non-calcareous, mixed, hypertermic typic Haplustalfs with silt loam texture (41% sand, 39% silt and 20% clay). The soil has 7.8 pH, electrical conductivity 0.32 dSm^-1, organic carbon 0.45%, Available phosphorus 33.5 kg ha^-1 and available potassium 82.5 kg ha^-1, the experimental site fall under potassium deficient category. The treatment includes application of potassium at the rate of 0, 15, 30, 60 and 90 kg K₂O ha^-1 applied using Murate of Potash (60% K₂O) at the time of sowing. The experiment was laid out using randomised complete block design with five treatments randomised in three blocks with plot size of 6.0 m length and 4.0 m breadth.
 
Crop management
 
The ‘Package of Practices for Rabi Crops’ Punjab Agricultural University, Ludhiana (Anonymous, 2016) for Lentil was followed for crop management. The sowing of the lentil cultivar LL699 @ 30 kg seed ha^-1, was done in the first week of the November during the year 2016, 2017 and 2018. The seed was treated with Captan @ 2g kg^-1 of seed. The sowing was done with row spacing of 22.5 cm with Pora method. The fertilizers were applied at the rate of 27 kg Urea (46% N) and 250 kg superphosphate (16% P₂O₅) per hectare at the time of sowing. The weeds were controlled by 2-3 hand weeding, whenever required. The crop was harvested when plants were dried up and pods were matured. Insect-pest and diseases were controlled following the Package of Practices for Rabi Crops’ Punjab Agricultural University, Ludhiana (Anonymous, 2016).
 
Growth and yield analysis
 
Plant height was measured with a meter scale. The number of branches per plant and number of pods per plant were counted manually from randomly selected 5 plants from each plot. The total biomass yield and grain yield was recorded on plot basis at 14% and 10% moisture content, respectively and were expressed in term of quintal (100 kg) per hectare (q ha^-1). The harvest index (HI) as the ratio of grain yield to the total biomass yield was calculated from grain and biomass yield. The data on 1000 seed weight (g) was recorded by weighing randomly selected 1000 seeds.

Soil and plant analysis
 
Soil samples were collected at depths ranging from 0-15 cm and 15-30 cm. A composite soil sample was prepared after pooling the samples taken from three randomly selected sites in the field. The soil was dried in the shade at room temperature and sieved through 2-mm sieve to removes roots and debris. The soil was ground using wooden mortar and pestle to pass through a 0.5 mm sieve for determination of organic carbon. The samples were also analyzed for pH [1:2 soil water ratios (w/v)], soil organic matter, available K and available P. The grains were ground and digested using the diacid method and grain K content was determined using Flamephotometer. Partial factor productivity (PFP_K) was calculated as ratio of yield from plot to the amount of K fertilizer applied to that plot. Agronomic efficiency (AE) was calculated:  
Where
Y is yield of plots with application of fertilizer, Y₀ yield of plots without fertilizer application and F is fertilizer applied. 
 
Statistical analysis
 
The data generated from the three-year experiment was pooled and analysed for analysis of variance using PROC GLM (SAS software 9.1, SAS institute Ltd., USA) (Table 1). The Duncan’s multiple range test (DMRT) was used for comparison of treatment means of pooled data. PROC CORR was used for correlation analysis between yield and yield attributes.
 

Effect of potassium application of the growth of lentil
 
The perusal of the data revealed that the application of potassium has improved the plant height over the control treatment (Table 2) although the difference in plant height was non-significant among the treatments in the year 2016-17, 2017-18 and 2018-19. The number of branches per plot were significantly higher in the treatments with the application of potassium as compared to the control treatment in the year 2016-17, 2017-18 and 2018-19. The treatment T₂ has significantly improved the number of branches per plant as compared to the control, however T₂ was statistically at par with treatments T₃ and T₄. Potassium application improved the availability of nutrients such as nitrogen and phosphorus (Sahai, 2004), that lead to better plant growth and a greater number of branches per plant. Similarly, Singh et al., (2011) reported that secondary branches per plants were increasing with increasing the level of nutrient.
 
  
 
The pods per plant increased with the increase in nutrient levels up to 60 kg K₂O ha^-1 however the effect of different K dose was significant as compared to control. The maximum number of pods per plant was observed in T₃ treatment where 60 kg K₂O ha^-1 was applied, that was statistically at par with that of T₂ and T₄ treatment during three years. This improvement in the growth attributing characters might be due to the fact that potassium acts as catalytic agent in activating a number of enzymes and synthesis of peptide bonds (Sahay et al., 2013). The results so obtained corroborates with the findings of Brar et al., (2004) who reported beneficial effect of K on growth and yield parameters of pea. Similar findings were recorded by Ali et al., (2008) who reported that the number of pod per plant was significantly affected by potassium deficiency. The maximum response to the potassium applied was observed at 30 kg K₂O ha^-1and the remaining levels (60 and 90 kg K₂O ha^-1) were at par with 30 K₂O ha^-1 applied. The results indicate that application of K fertilizer resulted in an increase in number of pods per plant. Ghildiyal (1992) also reported similar observations where the number of pods per plant increased with K application.
 
Effect of potassium application of the yield of lentil
 
The pooled biomass and grain yield data has shown (Table 2) significant effect of K application on the biomass and grain yield of the lentil crop. The results on biomass yield revealed that the significantly higher biomass yield was achieved in the treatment T₃ as compared to the control treatment that was statistically at par with the treatment T₂ and T₄ during the three years of the study. The data on the effect of K application showed that the highest seed yield was observed in the treatment T₄. The treatments with the application of potassium has significantly improved the grain yield of lentil as compared to the control treatment, however the T₂, T₃ and T₄ were statistically at par among themselves. Chakraborty (2009) also observed that the application of K fertilizers increased the lentil seed yield by 32% over the control treatment. The enhanced photosynthesis and translocation of photosynthates from source to the seeds as a result of increased enzymatic and other biological activities (Zeidan et al., 2006) may have improved the lentil yield. Potassium also helps in the developing resistance to crops against pests and diseases, that had improved the yield. Sahu et al., (2002) and Brar et al., (2004) reported similar findings. Ali et al., (2008) and Ganga et al., (2014) also reported higher yield with application of potassium as compared to control. The harvest index as a ratio of grain yield to biomass yield indicates the efficiency of plant to convert biomass to grain. The results (Table 2) doesn’t show any significant effect of K application on the harvest index of the crop as compared to the control treatment.
 
Effect of potassium application of the yield attributes and K uptake of lentil
 
The data on 1000-seeds weight of lentil as affected by K fertilizer application has been shown in Table 2. The results showed that 1000 seed weight of lentil was significantly enhanced with the application of K fertilizer, highest 1000 seed weight was observed in the T₂ treatment, however, 1000 seed weight in T₂ treatment was significantly higher as compared to control treatment, the 1000 seed weight in T₂ treatment was statistically at par with the T₃ and T₄. Khan et al., (2014) also observed that maximum 1000-seed weight of chickpea (Cicer arietinum) in the well fertilized treatments as compared to control. Jain and Tiwari (1997) also observed that the application of K along with other macronutrients in lentil produced maximum seed weight.
        
The grain K content was found affected by the K application (Table 2). The highest grain K content was observed in the treatment T₄, whereas no significant difference among the treatments T₂, T₃ and T₄ was observed. The grain K content in T₂, T₃ and T₄ treatments was significantly higher than that in control treatment during the study period. The total grain K uptake (Table 2) was calculated as the product of grain K content (%) to the grain yield from each plot. The highest total grain K uptake was observed in the T₄ (90 kg K₂O ha^-1) treatment that was statistically at par with treatment T₂ and T₃ and significantly higher than the control treatment during the three-year.
 
Effect of potassium application on the partial factor productivity K (PFP_K) and agronomic efficiency of lentil
 
The partial factor productivity (PFP_K) is long term trend indicator, indicating how productive the treatment in question in term of its nutrient input is. The data on the Partial Factor Productivity (PFP_K) (Fig 1) revealed highest factor productivity in the T₁ treatment followed by T₂, however partial factor productivity as a function of nutrient input followed exponential trend with correlation coefficient of 0.95. Thus, treatment T₂ may be recommended to get maximum productivity as the grain yield under this treatment is statistically at par with the T₃ and T₄ and significantly higher than the control.
 

        
The agronomic efficiency (AE) reveals the information about how productivity improved with a particular treatment over the control treatment. It is short term indicator of impact of applied nutrient on the productivity. This indicator is more useful in recommending nutrient considering the omission plot yields. The data on AE (Fig 2) revealed highest efficiency under T₁ (15 kg K₂O) treatment. The AE also found to be exponentially related to K₂O application (R² = 0.96), where agronomic efficiency declined with increasing the fertilizer dose. So, in the light of AE data, it is recommended that the 30 kg K₂O ha^-1 fertilizer may be applied in the potassium deficiency soils to achieve highest lentil productivity.
 

 
Correlation among plant growth, yield and yield attributes of lentil
 
The lentil grain yield showed positive and significant correlation with pods per plant (0.31), biomass yield (0.46) (Table 3). The 1000 grain weight was significantly correlated to the plant height (0.58), number of branches per plant (0.47), number of pods per plant (0.70) and negatively correlated to biomass yield (-0.182). The number of pods per plant was significantly correlated to the grain yield (0.31), 1000-grain weight (0.708), grain K content (0.64) and grain uptake (0.504). The grain K uptake was significantly correlated to plant height (0.33), pod per plant (0.50), biomass yield (0.52), grain yield (0.91), harvest index (0.42) and grain K content (0.87). It indicates that the K uptake was more where grain yield and biomass yield were higher.