Research Article

Maize Productivity as Influenced by Potassium under Reduced Irrigation Regimes

Salman Ali*, Inamullah, Muhammad Arif, Mehran Ali, Muhammad Owais Iqbal, Fazal Munsif and Arsalan Khan

Department of Agronomy, The University of Agriculture, Peshawar, Khyber Pakhtunkhwa, Pakistan.

Received | Febraury 21, 2018; Accepted | January 05, 2019; Published | February 10, 2019

*Correspondence | Salman Ali, Department of Agronomy, The University of Agriculture, Peshawar, Khyber Pakhtunkhwa, Pakistan; Email: salmankhan@aup.edu.pk

Citation | Ali, S., Inamullah, M. Arif, M. Ali, M.O. Iqbal, F. Munsif and A. Khan. 2019. Maize productivity as influenced by potassium under reduced irrigation regimes. Sarhad Journal of Agriculture, 35(1): 171-181.

DOI | http://dx.doi.org/10.17582/journal.sja/2019/35.1.171.181

Keywords | Irrigation, Potassium, Drought, Stress, Maize productivity, Yield

Introduction

Maize (Zea mays L.) is a C4, annual and exhaustive cereal crop which can be grown throughout the year around the world because of its photo thermo insensitive nature (Verma, 2011). It is grown mostly as an important grain crop and for fodder purpose. It is grown twice in a year (Spring and Autumn seasons) due to its short life cycle. Maize grains are used for many industrial purposes as in alcohol, starch and corn sugar industries. In Pakistan, the cultivated area under maize was 1.17 million ha while total production and average yield were 4.94 million tons and 4231 kg ha-1, respectively. Similarly, in KP, the cultivated area under maize was 0.471 million ha with 0.9148 tons’ annual production and 1945 kg ha-1 average yield (MNFSR, 2015).

Water is the fundamental part of a plant due to its pivotal role in plant growth and developmental process in plant life cycle. Availability of water at a proper growth stage in proper quantity is essential for higher and economical crop production (Aladabadi et al., 2009). Drought stress negatively affects crop yield in so many ways, therefore, the increasing deficit water scenario due to changing climatic conditions poses a serious threat to high productive agriculture and its sustainability. The damage to crop yield and production is more severe if the drought occurs at several stages of crop growth such as seedling establishment stage, vegetative stage, reproductive growth stage and grain filling stage (Reddy et al., 2004). Regarding the water requirement, the critical duration of maize growth is from the start of flowering to seed dough stage (Classen and Barber, 1977). Several researchers have shown huge losses in yield due to moisture deficit at this stage (Frootan and Yarnia, 2015). Grain yield can be reduced dramatically if drought stress occurs at flowering formation stage (Abo-El-Kheir and Mekki, 2007).

Drought stress occurs at different stage may have a different effect on yield because the physiological processes, water requirement and crop vulnerability to stress is different at each stage of crop growth (Ouda et al., 2006). For example, Pandey (2000) reported that water stress at male meiosis stage resulted in poor growth, reduced tassel development and chlorophyll contents of corn. Drought stress at vegetative stage may not affect the grain yield, but drought stress at grain filling stage can drastically reduce the grain yield by 50% or even more (Kirda et al., 2005). Innovations for saving water in irrigated agriculture by using proper method of irrigation and erasing extra and unnecessary irrigation are of great importance in water deficit regions especially arid and semiarid areas (Kisekka et al., 2015; Kirda et al., 2005). Therefore, application of irrigation water to the crop at proper growing or critical stage can reduce water losses by increasing water use efficiency without any adverse effect on yield.

Balanced fertilization of crop with recommended dose is essential for higher production. Being the lower fertility status of Pakistani soil and exhaustive nature of maize crop it is necessary to supply the required nutrients especially nitrogen (N), phosphorus (P) and potassium (K) in adequate amount (Iken and Amusa, 2004). Potassium is an essential nutrient for optimum plant growth and development (Zia-ul-hassan et al., 2011). Due to its major and important role in plant physiology and biochemistry, it is considered as one of the major plant nutrients (Nawaz et al., 2006). It promotes plant growth and enhances grain yield (Davis et al., 1996). Many studies have revealed the significant role of K fertilizers in reducing the adverse effects of drought stress on crop growth (Tabatabaii et al., 2001). In Pakistan, although most of the soils carry K in relatively large quantity but only a small fraction of it is available to plant (Zhang et al., 2014). K levels are getting depleted day after day due to extensive cultivation of high yielding and exhaustive crops and lower application of potassium to soil (0.8 kg ha-1 year-1) which may affect adversely the growth, productivity and ultimately yield of agricultural crops (Ahmad and Rashid, 2003). Reduction in yield due to lower soil K has already been observed in many parts of the country (Aslam et al., 2014).

Therefore, our study aims to evaluate the most appropriate irrigation times during the life cycle of maize and to find out the best level of potassium for higher yield and yield attributes of the maize crop.

Materials and Methods

Description of experimental site

A field trial was carried out at Agronomy Research Farm, The University of Agriculture Peshawar, in autumn season, 2015. The experimental site exhibits subtropical climatic conditions with an annual rainfall of 350 mm. Warsak canal is used to irrigate the research area. According to FAO soil classification, the soil of experimental site is categorized as Haplic Luvisols. Physio-chemical properties of the experimental site are listed in Table 1. Data regarding rainfall, maximum and minimum temperature during the crop growth cycle is given in Figure 1.

Experimental design and treatments

Randomized complete block design with split-plots arrangement was used to test the effects of various levels of potassium under reduced irrigation. Treatments were replicated three times. Five critical crop growth stages were selected from maize growth stage described by Darby and Lauer (2000). Treatments consisted of six irrigation frequencies; I0 (zero or control irrigation), I1 (irrigation at V1 stage), I2 (two irrigations; each at V1 and V7 stage), I3 (three irrigations; each at V1, V7 and VT stage), I4 (four irrigations; each at V1, V7, RT and R2 stage) and I5 (five irrigations; each at V1, V7, RT, R2 and R4 stage), allocated to main plots and five levels of potassium (0, 25, 50, 75 and 100 kg ha-1) assigned to subplots. Nitrogen from urea and phosphorus from DAP (Diammonium phosphate) were applied at the rate of 120 and 90 kg ha-1, respectively, whereas, the source of potassium was sulfate of potash (SOP). All the potassium and phosphorus fertilizers were applied at sowing time (19th June, 2015) of maize while nitrogen was applied in two splits; half at sowing time and a half at the V7 stage of crop growth.

Table 1: Soil physio-chemical properties of the experimental site.

Property	Unit	Value
Clay	%	3.5
Sand	%	46.5
Silt	%	50
Textural class		Silty clay loam
pH		7.54
EC	dS m-1	0.20
Total Potassium	mg kg-1	80.63
Total Phosphorus	mg kg-1	2.48
Total Nitrogen	mg kg-1	18.94
Total Organic Carbon	g kg-1	12.71

Field experiment agronomic practices

For this experiment, a subplot size of 2 m × 3 m was used having 4 rows, each 2 m long and 0.75 m apart. The field was ploughed on 19th June with the help of cultivator followed by rotavator at field capacity. High yielding and popular maize variety of maize (AZAM) was sown at the recommended seed rate (30 kg ha-1) on 19th June, 2015. Thinning was done on 6th July, 2015 after 10 days of crop emergence to maintain plant to plant distance of 25 cm and a uniform plant density (65000- 70000 plants ha-1). Weeding was done twice manually with help of hand hoe 20 and 40 days after emergence. Chloropyriphos insecticide was used for controlling maize stem borers in 0.006% concentration.

Data Recording Procedure

Plant height was recorded by selecting 10 random plants in each subplot and measuring their height from base to tip of the tassel. Grains were counted in five randomly selected ears in each subplot and then averaged to get an average number of grains ear-1. 1000-grain were counted and weighed from each subplot for recording thousand grains weight. Four rows of each subplot were harvested, sun-dried, weighed and then converted into biological yield kg ha-1 by the following formula.

Ears from harvested four rows were detached then dehusked and sun-dried before shelling. After proper drying, the cobs were shelled and grain yield (kg ha-1) was worked out using the following formula.

Statistical analysis

To analyze data statistically analysis of variance techniques suitable for randomized complete block design with split plot arrangement was used. Means of the treatments were compared through the least significant differences (LSD) test at 5% probability level (Jan et al., 2009).

Results and Discussion

Plant height (cm)

Irrigation frequencies and K levels significantly affected plant height of maize (Table 2; Figure 2a, c). Increasing number of irrigations from I1 to I5 increased plant height by 8, 10.2, 15, 15.7 and 19.7%, respectively over no irrigated plots (I0) and thus taller plants were recorded in plots irrigated five times (Figure 2a). Likewise, plant height increased with

increasing K levels; however, a maximum increase of 10.2% in plant height was noted with the application of 75 kg K ha-1 (Figure 2c). Further increase in potassium beyond 75 kg ha-1 did not show any noteworthy increase in plant height of maize. Short stature plants were observed in plots where no K was applied. The interaction between irrigation frequencies and K levels was not found significant (Table 2).

Grains ear-1

Statistical analysis of data showed significant effects of irrigation frequencies and K levels on grains ear-1 of maize (Table 2; Figure 3a, c). Increase in grains ear-1 was observed with increasing irrigation numbers from I1 to I5 and significantly higher grains ear-1 of maize were recorded under five irrigations (I5), while lower grains ear-1 were recorded with no irrigation (Figure 3a). Similarly, 75 kg ha-1 potassium application increased grains ear-1 by 22.6, 13.6, 4.5 and 5.1% over K0, K1, K2, and K4 treatments respectively, and resulted in higher grains ear-1, while lower K-controlled plots resulted in lower grains ear-1 (Figure 3c). Interaction of irrigation frequencies and K levels indicated a linear increase in grains ear-1 with increasing irrigation numbers and K fertilization from 0 to 75 kg ha-1. However, the increase was more prominent with five irrigation and 75 kg ha-1 K application, while further increase in K levels didn’t show any significant increase in grains ear-1 (Table 2; Figure 5a).

Thousand grains weight (g)

Irrigation frequencies and K fertilization significantly varied thousand grains weight of maize (Table 2; Figure 3b, d). Mean values of the data revealed heavier grains in plots supplied with five irrigations (I5) while lower thousand grains weight were recorded in no irrigated plots (Figure 3b). Likewise, application of 75 kg ha-1 K produced heavier grains with higher thousand grains weight, though lower thousand grains weight was recorded in K0 plots (Figure 3d). Interaction of irrigation frequencies and K fertilization indicated that thousand grains weight increased significantly with increasing irrigation numbers and K levels from 0 to 75 kg ha-1 but further increase in K levels (from 75 to 100 kg ha-1) showed no increase in thousand grains weight of maize (Table 2; Figure 5b). However, the increase was more noticeable when 75 kg ha-1 K was applied under five irrigations.

Grain yield (kg ha-1)

Data analysis showed that different irrigation frequencies and K application brought significant variations in grain yield of maize (Table 2; Figure 4a, c). Increasing number of irrigations from I1 to I5 increased grain yield by 16.9, 23.2, 25.3, 31.9 and 37.6% respectively, over no irrigated plots (I0), and hence five times irrigated plots produced higher grain yield as compared with rest (Figure 4a). Regarding K fertilization, grain yield increased with increasing K levels, however a maximum increase of 14.2% was observed with 75 kg ha-1 potassium application. Further increase in K beyond 75 kg ha-1 showed slight but non-significant reduction in grain yield (Figure 4c) whereas control K plots resulted in lower grain yield of maize. The interaction between irrigation and K fertilization indicated linear increase as grain yield increased with increasing irrigation numbers and K levels and thus higher grain yield was recorded with five irrigations and 75 kg ha-1 K fertilization (Table 2; Figure 6a).

Biological yield (kg ha-1)

Irrigation frequencies and K fertilization significantly affected biological yield of maize (Table 2; Figure 2b, d). Increase in biological yield was witnessed with

Table 2: Two-way analysis to find out the effects of irrigation frequencies and potassium application on maize yield.

Treatments	Crop variables	Df	F-Value	Probability
Irrigation Frequencies	Plant height	5	6.955	<0.01
	Grains ear-1	5	132.231	<0.001
	Thousand grains weight	5	98.094	<0.001
	Biological yield	5	80.112	<0.001
	Grain yield	5	51.253	<0.001
	Harvest index	5	18.220	<0.001
Potassium Levels	Plant height	4	8.636	<0.001
	Grains ear-1	4	133.497	<0.001
	Thousand grains weight	4	40.327	<0.001
	Biological yield	4	63.488	<0.001
	Grain yield	4	51.377	<0.001
	Harvest index	4	8.049	<0.001
Irrigation x Potassium	Plant height	20	0.297	NS
	Grains ear-1	20	2.765	<0.01
	Thousand grains weight	20	2.052	<0.05
	Biological yield	20	0.894	NS
	Grain yield	20	1.877	<0.05
	Harvest index	20	2.231	<0.01

Ns: Non-significant.

increasing irrigation numbers and significantly higher biological yield was noted in plots irrigated five times as compared with other treatments, whereas lower biological yield was recorded with no irrigation (Figure 2b). Similarly, K fertilization at the rate of 75 kg ha-1 enhanced biological yield by 10.5, 5.1, 2.7 and 2.1% over K0, K1, K2, and K4 treatments respectively, and resulted in higher biological yield. However, increasing K beyond 75 kg ha-1 did not show any significant changes in biological yield of maize. Plots with no potassium resulted in a lower biological yield of maize.

Harvest index (%)

Data analysis revealed significant differences in harvest index of maize in response to various irrigation frequencies and K fertilization (Table 2; Figure 4b, d). Increasing irrigation numbers from I0 to I5 significantly increased harvest index of maize and higher harvest index was recorded in five times irrigated plots (I5), while lower harvest index was recorded in no irrigated plots (I0) (Figure 4b).Similarly, harvest index increased with increasing K levels, however, maximum increase of 3.2% was observed with 75 kg ha-1 K application. Further increase in K beyond 75 kg ha-1 showed a slight reduction (1.6%) in harvest index (Figure 4d). Lower harvest index was recorded in plots where no K was applied. The interaction between irrigation and K fertilization indicated a linear and positive increase in harvest index with increasing irrigation numbers and K levels and thus higher harvest index was recorded with five irrigations and 75 kg ha-1 K fertilization (Table 2; Figure 6b).

Plant height is an important factor which reflects the active growth attained during the life cycle of crop. Increase in irrigation numbers significantly increased plant height of maize. Taller plants were observed in plots irrigated five times while short height plants were recorded in no irrigated plots. The possible reason might be the availability of water at desired crop growth stage improved water uptake, increased photosynthesis and photosynthates, resulting in better growth. Similar results were reported by Anjum et al. (2014) who reported taller maize plants with optimum supply of irrigation water. Babar et al. (2015) also reported increased plant height with application of optimum irrigation water. Taller plants were noted in plots that received 75 kg ha-1K while short stature plants were recorded in control K plots.

Findings of Pettigrew (2008) and Cheema et al. (1999) agree with our results, who stated increase in plant height with increasing application of K fertilizers. Similarly, Stone et al. (2001) and Pandey et al. (2000) also stated that plant height increased with increasing irrigation frequencies and potassium application levels. Maqsood et al. (2001) and Ayub et al. (2002) also stated that plant height increased with increasing potassium fertilizers application.

Grains weight determines the seed vigor, higher the seed weight the higher will be seed vigor and so the economic yield. Plots irrigated five times produced significantly higher grains ear-1 and 1000-grain weight as compared with no irrigated plots. Similarly, increasing K fertilization also showed increase in 1000-grain weight and grains ear-1 of maize. The reason for reduction in grains ear-1 and 1000-grain weight in no irrigated or less irrigated plots in comparison with plots irrigated five times might be due to the water stress at different active growth stages that affected the grains formation and assimilates translocation

from source to grains (Ahmad et al., 2002). Kuşçu and Demir (2012) reported higher grains ear-1 with increasing irrigation water as compared with no irrigated plots. Aguilar et al. (2007) stated more grains ear-1 and higher thousand weight of maize under high irrigation frequencies. Similarly, Bahrani et al. (2012) also suggested higher 1000-grain weight of maize with frequent supply of irrigation water at proper intervals. Maqsood et al. (2013) stated significantly heavier grains and higher grains ear-1 with higher application of potassium. Confirmatory findings were reported by Hussain et al. (2007) and Aslam et al. (2014) who suggested increase in 1000-grain weight and grains ear-1 with increasing potassium fertilization.

Increasing irrigation numbers and K levels significantly increased biological yield and grain yield of maize. Higher biological and grain yield was observed in plots irrigated five times while lower biological yield were recorded in no irrigated plots. Similarly, increase in K levels also increased biological and grain yield of maize. The possible reason might be that uniform supply of moisture at critical crop growth stage resulted in better crop growth, crop stand and photosynthates formation which ultimately increased biological and grain yield of maize. Our results confirm the findings reported by Maqsood et al. (2013) and Bahrani et al. (2012), who revealed higher biological and grain yield with full irrigation as compared with reduced irrigation frequencies. The probable reason for increase in biological and grain yield with K application might be due to improved roots growth which resulted in better moisture uptake and utilization and crop survival under severe drought conditions (Pettigrew, 2008). In order to make sure that crop get all the nutrients, they must be applied in appropriate amount. Optimum level of fertilizers is that at which crop respond better and utilize it more efficiently. Deficit fertilizers application reduces crop yield while excessive fertilizers application increases input cost, environmental and water pollution and reduces crop yield resulting in very low net return per unit area. Datnoff (2007) reported that K application higher than optimal levels doesn’t increase maize yield and disease resistance. The reason for decrease in maize yield with increasing K levels beyond 75 kg ha-1 might be that excessive K fertilization hindered the uptake of other nutrients like Zinc, iron, Manganese and Magnesium (Zhao et al., 2011). Also the genetic makeup of some cultivars make them less or more K efficient and thus making their K requirement and uptake different (Dantoff, 2007). Confirmatory results were reported by Aslam et al. (2013) who reported higher biological and grain yield with optimum application of K fertilizers. Our results are also in line with those of Bukhsh et al. (2009), Tariq et al. (2011), Cheema et al. (1999) and Maqsood et al. (2013).

Harvest index determines the potential of a crop to transform the produced dry matter to economic yield. Significantly higher harvest index was recorded in fully irrigated plots as compared with no irrigated plots. Likewise, plots fertilized with 75 kg ha-1 potassium produced higher harvest index as compared with plots where no K was applied. Similar results were reported by Aslam et al. (2014) who reported a higher harvest index under full irrigation at optimum intervals and proper crop growth stages as compared with deficit irrigation. Bahrani et al. (2012) and Tariq et al. (2011) also stated a higher harvest index with the increase in K application and numbers of irrigation.

Conclusions and Recommendations

In the light of results and discussion, it was concluded that water stress at each critical crop growth stage drastically decreased the growth and yield of the crop. Optimum water supply to crop considering the growth stage of crop and weather condition can increase the yield. Therefore, among all the treatments, plots received five irrigations each at V2, V7, VT, R2 and R4 stage and 75 kg ha-1 potassium application improved crop yield and yield components as compared with the rest of the treatments.

On the basis of higher grain yield and yield components and efficient water utilization, five irrigations each at V1, V7, VT, R2 and R4 stage with 75 kg ha-1 K application are recommended throughout the lifespan of maize crop for enhancing yield and productivity of maize in agro-ecological zones of KP.

Author’s Contribution

Salman Ali: Conducted the field experi-ment and responsible for all field work from sowing to harvesting and manuscript write up.

Inamullah: Major supervisor, responsible for overall planning and super-vision of the experiment.

Muhammad Arif: Minor field supervisor, re-sponsible for supervision of the experiment at field level.

Mehran Ali: Statistical analysis, figures and tables development.

Muhammad Owais Iqbal: Literature review and helped in results and discussion write up.

Fazal Munsif: Helped in manuscript write up and formatting, and review.

Arsalan Khan: Agronomic practices manage-ment in field including weeds and irrigation management during the course of experi-ment.

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