Effect of Potassium Application on Crop Yields under Wheat- Rice System

A field experiment was conducted to study the response of wheat and rice to potassium during 2004-05. The basal dose of N at 120 kg, P2O5 at 90 kg ha -1 was applied with K levels to both wheat and rice crops. Wheat variety Naseer 2000 and rice variety IRRI 6 were used in the study. The experiment was carried out in R.C.B design with three replications. Potassium application significantly increased the grain yield of wheat from 2468 kg ha in the control to 2789 kg ha in the treatment receiving K at 60 kg ha giving an increase of 13 % over control. The number of tillers, spikes, spike length and plant height of wheat were also significantly increased by K application. The rice also showed positive response to K application and hence both yield and yield parameters were significantly greater in the K than in the check treatment. Paddy yield was increased significantly by K application up to 50 % over control. The number of spikes plant, spike length and 1000 grain weight were also significantly increased by K application over control. The application of K significantly increased the number of spike m and plant height over control, but differences among K treatments were non-significant. The highest increase of 50% over control in paddy yield was recorded in treatment receiving K by both wheat and rice each time at 60 kg K2O ha . Potash applied to previous wheat increase paddy yield by 30.9% over control. The highest VCR (3.9:1) was obtained with treatment receiving K by rice only, the lowest VCR (2.0:1) was achieved with treatment receiving K by both wheat and rice. INTRODUCTION In Pakistan, wheat and rice are the major national food grain crops. In order to feed its rapidly growing population the wheat is going to be imported. If the productivity of rice wheat system is not enhanced and population growth is not checked the situation will be aggravated. Despite the prime position of wheat and rice in the food and the economy of the country, productivity of rice-wheat cropping system is poor. The average yield of wheat in Punjab, Sindh and NWFP is 2.50, 1.70 and 1.38 t ha, respectively while for rice it is 2.47, 2.50 and 2.12 t ha in respective provinces. However, the national average yield of wheat and rice has been reported as 2.37 t ha 1 and 1.97 t ha, respectively (MINFAL, 2004). There is evidence that productivity of the system is declining. Since rice-wheat is highly nutrient exhaustive production system, it may result in nutrient imbalance in the soil. It is believed that irrational use of fertilizer and nutrients imbalance in soil are major factors for poor crop yields in ricewheat system (NFDC, 1994). Potassium is one of the major essential plant nutrient required for normal growth and development of plants. It is the essential plant food element more frequently found in larger quantities in crop plants than any other element. Before the introduction of new high yielding fertilizer responsive varieties and intensive use of nitrogen, the soils were not stressed for their potassium supply. As a result of more intensive cropping system, use of high yielding varieties and the imbalanced use of nitrogen, lack of potassium is now increasingly becoming limiting factor in soil that were previously considered to have sufficient available potassium. Correction of wide spread phosphorus deficienceies has been another factor that has contributed to a better response of rice to potassium application. Crop removal of nutrients is one of the main reasons for deterioration of soil fertility. It has been reported that 4 t ha of rice, remove 100 kg K2O from the soil (IPI, 1974). If this removal is not replenished, yield may decline sooner or later. Due to continuous use of high yielding varieties and recommended levels of nitrogen and phosphorus soils are being depleted of other essential elements especially potassium. Though the yields are not affected much, the potash status of the soils is going down and consequently the yields are likely to decrease. It has been reported by (IPI, 1986) the average rice yield increased 17 percent due to potash application. Bhatti et al. (1981) concluded from their research that 90 K2O ha -1 proved to be economical dose of potash for paddy. Rehman et al. (1982) and Krishnan (1977) concluded from their research that an application of 60 kg K2O ha -1 potash is economical. Khattak and Bhatti (1986) conducted research work on the residual effect of phosphorus and potassium on the yield of maize and wheat. They found that P applied to the first crop was sufficient for the subsequent second and third crop. Potassium applied to the first crop may be sufficient up to fourth or even fifth crop. The levels applied were 50 and 100 kg K2O ha . Siddique et al. (1997) reported that 110 kg K2O ha -1 was sufficient for optimum yield of wheat. Nabhan et al. (1989) and Krauss et al. (1996) advocated that soils having relatively high contents of * Arid Zone Research Institute, D.I.Khan – Pakistan. ** National Agricultural Research Centre Islamabad – Pakistan. *** Pakistan Agricultural Research Council, Islamabad – Pakistan. Rahmatullah Khan, et al. Effect of potassium application under wheat-rice system ...... 278 potassium showing high response to applied K and vice versa. Hussain and Yasin (2003) who found an increase of 21 % and 35 % in wheat and paddy by the application of 40 kg K ha. A lot of work has been conducted in NWFP to find out the optimum level of potash for wheat and rice but a little work has been done on percent increase of yield over control by the direct, residual and cumulative effect of potash in wheat-rice system. Hence keeping in view of the above facts the present study was planned to study the effect of potassium application on wheat and rice under wheat-rice system. MATERIALS AND METHODS A field experiment was conducted during 2004-05 to study the effect of potassium on wheat and rice crops. The experiment was laid out at Arid Zone Research Farm D.I.Khan in Randomized Complete Block Design with three replications. The experiment was comprised of five treatments, check having NP only (T1), 60 kg K2O ha -1 to wheat and nil to rice (T2), nil to wheat and 60 kg K2O ha -1 to rice (T3), 60 kg K2O ha to wheat and nil to rice (T4), 30 kg K2O ha -1 each to wheat and rice (T5). A basal dose of N at 120 kg and P at 90 kg ha was applied to all treatments plots. The sources for N, P and K were urea, TSP and SOP, respectively. All P2O5, K2O and half N was applied at sowing while remaining half N in wheat was applied at 2 irrigation and in rice at panicle initiation. The wheat variety Naseer 2000 and rice variety IRRI 6 has been planted during the study. The wheat was sown during 2 week of November 2004 while rice was planted on the 1 week of June 2005. The treatment plot size of 2.40 m x 6.00 m was kept for both the crops as rice was planted in same layout of wheat. All the other cultural practices were followed uniformly throughout the growing season. A composite soil sample was taken before the commencement of the study. The soil was analyzed for various physico-chemical characteristics (Table I). Electrical conductivity and pH of the soil were determined in 1:2 soil water suspension method according to Black (1965). Soil texture was determined by the hydrometer method (Moodie et al., 1954) whereas lime was estimated by acid neutralization method (Richards, 1954). Organic matter was determined by the modified method of Walkley and Black (Nelson and Sommers, 1982). Olsen P and NH4OAC extractable K were determined according to (Black, 1965). The number of tillers m, spike m, spike length and plant height in wheat and rice were recorded at proper time. The net plot of 0.60 m x 5.00 m was harvested manually for 1000 grain weight and grain yield of both wheat and rice. All the relevant data was statistically analyzed using MSTATC computer program. Table I Physico-chemical characteristics of soil Soil properties Unit Value pH (1:2) 8.00 E.C (1:2) dSm 0.450 CaCo3 equivalent % 10.50 Organic matter % 0.75 Nitrogen % 0.037 NaHCO3 Olsen P (mg kg ) 5.0 NH4OAC Extractable K (mg kg ) 80 Sand % 25.0 Silt % 40.0 Clay % 35.0 Textural class Silty Clay RESULTS AND DISCUSSION The results revealed that grain yield of wheat were significantly increased by K fertilization compared with the control treatment (Table II). The highest grain yield of 2789 kg ha was obtained from 60 kg K2O ha -1 giving an increase of 13 percent over control. The K level at 30 kg K2O ha -1 produced significantly lower grain yield of 2529 kg ha which was statistically at par with check (no potash). The application of K at any level had no significant effect on 1000 grain weight. The highest number of tillers (497 m) and spike m (363) were achieved with application of potash at 60 kg K2O ha . The lowest number of tillers m (444) and spikes m (283) were obtained from check. The plant height of wheat was also significantly affected by K application. The maximum height of 102 cm was attained with the application of potash at 60 kg K2O ha -1 while minimum from check. Spike length of wheat was not affected significantly by any of the K levels. The data obtained on rice crop after wheat revealed that grain yield of paddy was significantly increased Sarhad J. Agric. Vol. 23, No. 22007 279 by K application (Table III). The maximum paddy yield of 6053 kg ha was obtained from the treatment receiving 60 kg K2O ha -1 during both wheat and rice crops. This treatment increased the yield by 50 % over control. A significant response was also noticed in term of plant height due to K application. The maximum plant height of 111.8 cm was achieved with the application of potash at 60 kg K2O ha -1 both to wheat and rice crops. K levels also significantly affected the 1000 grain weight. The 60 kg K2O ha -1 applied both to wheat and to subsequent rice produced heaviest grains 22.72 g compared with 21.58 g from check. Similarly number of spikes plant and spike length were also affected significantly over check which ranged from 16.8 to 26.1 and 21.1 to 25.7 cm, respectively. The cumulative effect of 60 kg K2O ha -1 application resulted in greatest number of spikes plant and spike length while the lowest number of spikes plant and spike length was recorded in check. The number of spike m was also significantly increased by K fertilization, however differences among K treatments were non significant. The number of spike m ranged from 272 to 329. Highest number of spikes were achieved from 60 kg K2O ha -1 applied both to wheat and rice crop while the lowest from check. Significant difference in number of spikes plant was observed when K was applied individually to either wheat or rice crop or to both the crops. Percent increase in grain yield due to residual, direct and cumulative effect of 60 kg K2O ha -1 application was 30.9 %, 47.3 % and 50 % over control. The economics of the fertilizer use (K) revealed that the highest value cost ratio (VCR) of (3.9:1) was recorded from application of 60 kg K2O ha to rice crop, while minimum VCR (2.0:1) with highest net return of Rs.9101 ha was achieved from application of 60 kg K2O ha -1 each to both wheat and rice (Table. VI). It can be concluded from above application of K increased the yield over control and also the increase was economical either applied to wheat and rice or only to rice crop. These results are in agreement with Rehman et al., 1982 and Krishnan 1977 who concluded that an application of 60 kg K2O ha potash is economical. Nebhan et al (1989) and Krauss et al. (1996) advocated that soils having relatively high content of potassium showing high response to applied K and vice versa. Khattak and Bhatti (1986) also highlighted the residual effect of K. Hussain and Yasin (2003) reported an increase of 21% and 35% in wheat and paddy respectively by the application of 40 kg K2O ha . CONCLUSION Potassium application significantly increased the grain yield of wheat and rice by 13% and 50% over control respectively. Application of 60 kg K2O ha to a single crop is more economical then application to both the crops. Table II Wheat response to Potassium application in wheatrice system