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Patterns of dry matter accumulation and grain yield of three corn hybrids under varying planting density/row spacings

Manzoor Ahmad1, Abdul Khaliq2 and Riaz Ahmad3

Department of Agronomy, University of Agriculture, Faisalabad 38040 Pakistan 1Email


Increasing population growth globally, and in Pakistan in particular, has evidently produced a food security problem. Corn is 3rd most important cereal crop after only wheat and rice. Yield gaps in production necessitate efforts for improving corn yields in developing countries. Modern hybrids respond differently to increasing plant density/row spacing, which has a considerable effect on the yield. Studies were undertaken for two years on the patterns of dry matter accumulation and the variation in yield of three corn hybrids belonging to different maturity groups. DK-919 (early) produced 19 and 8% more total dry matter (TDM) over DK-5219 (medium) and Pioneer-30Y87 (late) hybrids, respectively. TDM increased by 15% and 14% with increasing plant density from 6 to 8 plants/m2 and 8 to 10 plants m-2, respectively. DK-919 produced grain yield of 6437 kg /ha that was 6 and 17% higher than that recorded for Pioneer-30Y87 and DK-5219. Increase in grain yield by increasing plant density from 6 to 8 plants/m2 was in the range of 15 to 30% in all the hybrids. Increasing plant density of DK-919 and DK-5219 from 6 to 10 plants/m2 resulted in grain yield enhancement of 31 and 11% respectively. DK-5219 showed a different response wherein grain yield decreased by 6-8% when plant density increased from 8 to 10 plants/m2.

Key Words

Plant population, planting geometry, density tolerance, maturity groups.


Appropriate planting geometry is of utmost importance for realizing higher yields in modern corn hybrids. Plant population is the factor that changed most during the past six decades as a result of tolerance of newly introduced hybrids to high plant populations (Tollenaar & Lee, 2002). Periodic assessment of optimal plant density for corn that may vary with location is a continuous phenomenon, and is an outcome of continued genetic improvement in ability of corn hybrids to withstand higher plant densities. The information on forming suitable plant population for each corn cultivar is key factor for planning a successful production plan (Bavec & Bavec, 2002). Stand density affects plant architecture, alters growth and developmental patterns, influences carbohydrate production and partition in maize (Casal et al., 1985). However, Liu et al. (2004) concluded that corn plant height, leaf area index, dry matter accumulation, net assimilation as well as harvest index were not significantly affected by varying plant spacing. Alford et al. (2004) also stated that row spacing has no effect on corn grain yield. Such conflicting reports have led to renewed interests in the effects of high plant population densities on corn grain yield. It is even truer for newly evolved hybrids which have a wider range of adaptability to different micro and macro environments affecting their growth compared to older genotypes. An array of corn hybrids belonging to different maturity groups with varying adaptability to different environments, and management options are available for general cultivation the world over. Present study was conducted to quantify the patterns of dry matter accumulation and to determine optimum planting density for three corn hybrids.


Three corn hybrids early (DK-919, 100-105 days), mid (DK-5219, 105-115days), and late (Pioneer-30Y87, 115-125days) were grown at the Agronomic Research Area, University of Agriculture, Faisalabad, Pakistan for two successive seasons during autumn season. The climate of the region was subtropical to semi-arid. The experimental area was located at 73o East longitude, 31o North latitude and at an altitude of 135 m above mean sea level. Soil samples drawn up to a depth of 30 cm revealed that the soil was sandy loam in nature with a pH of 7.8, EC 0.5 dS/m, 0.905 % organic matter, 0.055 % total nitrogen, 8.35 ppm available phosphorus and 144 ppm available potassium. Experiments were laid out in randomized complete block design (RCBD) with split plot arrangement and replicated four times. Six rows (7 m length) of each hybrid were sown in main plots at row spacing of 45 cm (98765 plants /ha or 10 plants/m2), 60 cm (74074 plants/ha or 8 plants/m2) and 75 cm (59259 plants/ha or 6 plants/m2) in sub plots with plant to plant distance of 22.5 cm in each case during 1st week of August each year; throughout the rest of the paper these treatments are referred to simply by their densities. Trials were harvested as and when physiological maturity was achieved by each hybrid during both the years. Sowing was done by dibbling 2 seeds per hill. N, P2O5 and K at 150, 100, 100 kg/ha, respectively, was applied in the form of urea, diammonium phosphate and potassium sulphate. One third of the N, and all phosphorus and potash were applied at the time of sowing, while 1/3 nitrogen was applied at vegetative stage (30 DAS) and at reproductive stage (60 DAS). Six harvests including final harvest were made in both the experiments during both years. At each harvest, three plants were selected from each plot leaving appropriate borders. The plants were cut at the ground level on all the harvest dates. Fresh weights of sampled plants were recorded separately for each treatment and an appropriate sub-sample was oven dried to a constant dry weight at 70 C 3 to estimate biomass. Two central rows from each sub plot were harvested at physiological maturity; the cobs were air-dried and threshed manually. Grain weight was recorded (13% moisture content), and converted to kg/ha. Data collected were analyzed statistically using Fisher’s analysis of variance techniques and LSD test (P=0.05) was used to compare the differences among treatments’ means (Steel et al., 1997). Year effects were not significant, hence results on individual years are presented.


Total dry matter

Patterns of dry matter accumulation revealed non-significant difference amongst corn hybrids at the pre-anthesis stage (Fig. 3). Dry matter accumulation after anthesis accounted for most of the biomass in all hybrids at all three row spacings. TDM at final harvest varied significantly (P≤0.05) amongst hybrids (Table 1). DK-919 yielded highest TDM, 19 and 8% more than DK-5219 and Pioneer-30Y87, respectively. Total dry matter at final harvest was significantly (P≤0.05) affected by planting density (Table 1). TDM of corn sown at density of 8 and 10 plants/m2 was 14% and 34% higher than that recorded for crop planted at 6 plants/m2, respectively. The interaction between corn hybrids and planting density was only significant (P≤0.05) during 2007 indicating that TDM yield response depended upon hybrid and planting density during that year (Table 1). Increasing plant density from 6 to 10 plants/m2 improved TDM by 29%. On average, TDM production increased by 15% for each increase of 2 plants/m2 (Fig 2). TDM was positively correlated with plant density and regression accounted for 99, 95 and 99 % of variance in total dry matter yield owing to planting density for DK-919, DK-5219 and Pioneer-30Y87, respectively (Fig 3).

Grain yield

Significant differences were observed for grain yield amongst hybrids. DK-919 produced highest average grain yield of 6437 kg /ha, 6 and 17% higher than grain yield of Pioneer-30Y87 and DK-5219 hybrids, respectively (Table 1). Row spacing had a significant bearing upon grain yield and the highest yield (6541 kg /ha) was recorded when corn was planted at density of 10 plants/m2. Increasing density from 6 to 10 plants/ m2 resulted in 21 and 27% yield increase that ranged from 14 and 21% when density increased from 6 to 8 plants/m2 and 5 and 7 % for increasing density from 8 to 10 plants/m2 (Table 1). Increasing density in DK-919 and DK-5219 from 6 to 10 plants/m2 resulted in grain yield enhancement of 31 and 11%, respectively (Fig. 3). Nonetheless, in Pioneer-30Y87 grain yield increased by 34% during 2007 that was only 23% during 2006. DK-5219 showed a different response in terms of grain yield wherein it was decreased by 6-8% when density increased from 8 to 10 plants m-2.


Significant difference in total dry matter (TDM) at final harvest among hybrids was observed in present studies. Differences in yield often arise due to growth periods of specific hybrids which are modified further because of the genetic makeup and geographical origin of the hybrids. Number and architecture of leaves influences the performance of different hybrids in terms of yield. Gardner et al. (1990a) reported that modern maize hybrid accumulated substantially more dry matter per unit area than ancient races of maize. TDM was negatively correlated with row spacing (Fig 2). Yield potential of different hybrids varies to great extent depending upon their morpho-physiological attributes and genetic potential. Increasing plant density (narrowing the row spacing from 75 cm to 45 cm) resulted in 21-27% yield increase during both the years that ranged from 14-21% when row spacing was reduced from 75 cm to 60 cm. This showed greater potential for yield enhancement when shifting from 75 cm row spacing to 45 cm directly. Corn has been identified as being more sensitive to variations in plant density than other grasses (Almeida and Sangoi, 1996), and yield advantages of corn hybrids have been associated with increasing planting densities. Shapiro and Wortmann (2006) reported that maize grain yield typically exhibits a quadratic response to plant density with a non linear increase across a range of low densities a gradually decreasing rate of yield increase relative to density increase and finally a yield plateau at some relatively high plant density. Results for variation in grain yield among different corn hybrids are supported by many previous findings (Gradner et al., 1990a&b; Cox, 1996). Relatively higher harvest indices were observed for high yielding hybrids as compared with DK-5219 which was intolerant to higher plant densities ((Fig. 3). Higher yield potential of later-maturing hybrids and higher plant populations has been reported by Norwood (2001). Sarvari et al. (2002) stated that corn hybrids respond differently to increased plant density.

Table 1. Effect of row spacing on total dry matter and grain yield of three maize hybrids.


Total dry matter (kg /ha )

Grain yield (kg /ha)









17649 a

17168 a


6577 a

6298 a



15131 b

14306 c


5652 c

5353 c


Pioneer -30Y87

16921 a

15529 b


6183 b

5940 b


LSD (P ≤ 0.05)














Row spacing: (cm)


14287 c

13464 c


5494 c

5066 c



16336 b

15470 b


6244 b

6116 b



19078 a

18070 a


6673 a

6409 a


LSD (P ≤ 0.05)















H x S














Figures in the same column with different letters differ significantly at P ≤ 0.05 by LSD test.

Total dry matter (g m-2 d-1)


Days after sowing

Figure 1 Patterns of total dry matter with time. Comparison of different hybrids and row spacing a) 2006, b) 2007

Total dry matter (kg ha-1)

Planting density /Row spacing

Figure 2. Relationship between row spacing on total dry matter (kg /ha) of three maize hybrids during a) 2006, b) 2007

Grain yield kg ha-1

Row spacing/plant density

Figure 3. Influence of row spacing on grain yield of three maize hybrids during a) 2006 and b) 2007


Two years field experiments demonstrated that corn hybrid DK-919 (an early maturing) should preferably be grown at narrow rows (45 cm) for obtaining higher grain yields, while mid-season hybrid DK-5219 need to be planted at 60 cm row spacing. Late season hybrid Pioneer-30Y87 also exhibited highest grain at 45 cm row spacing.


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