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Planting Date and Cultivar Effects on Grain Yield in Dryland Corn Production

International Institute of Tropical Agriculture, Nigeria, c/o IITA Ltd. Carolyn House, 26 Dingwall Road, Croydon CR9 3EE UK

^* Corresponding author (A.Kamara{at}cgiar.org).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Corn (Zea mays L.) production is gradually spreading into the Sudan savanna zone of West Africa where production is limited by erratic and inadequate rainfall. To increase corn production, production practices should be properly designed to minimize the effects of low precipitation and high temperatures that characterize the zone. A study, to determine the performance of late (120 d), early (90 d), and extra-early maturing (80 d) corn cultivars over a range of planting dates, was performed in the Sudan savannas of northeast Nigeria. Delaying planting generally increased days to flowering and the anthesis-silking interval (ASI) and reduced dry matter production and yield and yield components. In Azir, planting of corn on 13 July reduced grain yield by 42% in 2006 because of a dry spell during crop establishment. Delaying planting to 21 and 28 July also reduced grain yield by 19 and 28.5%, respectively over the 2 yr. Averaged over the 2-yr yield reduction was 29.5 and 42% when corn was planted on 21 and 28 July, respectively in Damboa. There was no interaction between planting date and corn cultivar for days to silking, ASI, and grain yield suggesting that the cultivars responded similarly to planting date. The extra-early maturing cultivar, 95 TZEE-W, produced highest dry matter, harvest index, and grain yield at all planting dates suggesting that this cultivar is the most suitable in both locations. To reduce risk of drought stress, extra-early maturing corn cultivars should be planted in the Sudan savanna between the last week of June and the first week of July.

Abbreviations: ASI, anthesis-silking interval • HI, harvest index • WAP, weeks after planting

Received for publication March 22, 2008.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Corn is gradually replacing the traditional cereal crops such as sorghum [Sorghum bicolor (L.) Moench] and pearl millet [Pennisetum glaucum (L.) R. Br.] in the dry savannas of West and Central Africa particularly in areas with good access to fertilizer inputs and markets (Manyong et al., 1996; CIMMYT, 1990). Environmental conditions (such as high temperatures and high solar radiation) in the Guinea savannas are more suitable to corn production and yield is greater in comparison to the humid forest zone, which is the traditional area for corn cultivation (Kassam et al., 1975). In Nigeria, corn is primarily grown in the southern (latitudes 7°4' and 8°7' N; longitudes 4°1' and 12°2' E) and northern (latitudes 9°4' and 11°5' N; longitudes 3°8' and 13°1' E) Guinea savannas where the length of growing period is 120 to180 d and the rainfall is 1000 to1200 mm with a monomodal pattern and low likelihood of drought during late June to late September (Carsky and Iwuafor, 1999). Based on the climatic conditions, it is possible to attain 80% of maximum yield in these zones (Jagtap, 1995). For this reason, corn has been extensively adopted in the Guinea savannas of Nigeria (Manyong et al., 1996).

Because of the cash potential of corn, production is gradually spreading into the Sudan savanna zone of West Africa. The Sudan savanna zone extends between latitudes 9°30' and 12°31' N and longitudes 4° to 14°30' E and occupies about 12 million hectares (Manyong et al., 1996). Rainfall in this region is monomodal and ranges between 500 and 800 mm per annum with a growing season of about 100 to120 d (Ogungbile et al., 1998). Because of the semiarid climate, it is difficult to predict the start of effective rains at the beginning of the cropping season. In addition to the parasitic weed, striga [Striga hermonthica (Del.) Benth], corn production in the Sudan savanna zone is limited by short growing period and recurrent drought. The risk of drought is high in the Sudan savanna zone because rainfall is unreliable and its distribution is erratic (Eckebil, 1991). Annual corn yield loss due to recurrent drought is about 15% in sub-Saharan Africa (Edmeades et al., 1993). However, losses in the Sudan savanna may be greater especially where rainfall is around 500 mm or less (Badu-Apraku et al., 1997). Corn is sensitive to drought during the seedling stage, flowering, and grain-filling periods (Edmeades et al., 1993). Drought, which occurs at the seedling stage affects crop establishment, necessitating farmers to replant their crops (Kamara et al., 2003). With limited access to seeds, replanting is virtually impossible in the Sudan savannas of Nigeria. Drought, which coincides with flowering and grain-filling periods, can cause serious yield instability at the farm level, as it allows no opportunity for farmers to replant or otherwise compensate for loss of yield (Kamara et al., 2003). Despite the popularity of corn, farmers in the Sudan savanna zone do not have appropriate cultivars that are adapted to the short rainy season found in this zone.

To increase corn production in the Sudan savanna, production practices should be properly designed to tolerate the low precipitation and high temperatures that characterize the zone. Growing adaptable corn cultivars and choosing optimum planting dates are avenues to increase yields that farmers can adopt. Because of the short growing season, early and extra-early maturing corn cultivars with drought tolerance are desired. The International Institute of Tropical Agriculture (IITA) and the West and Central Africa Collaborative Maize Network (WECAMAN) have developed early and extra-maturing corn cultivars (Badu-Apraku et al., 1997) that can fit into the growing period of the Sudan savannas. These cultivars flower within 45 d after planting and mature between 75 and 80 d. Because of the extra earliness of these cultivars, they can grow and mature before the cessation of rains in the Sudan savanna zone. Yield potential of these cultivars are however lower than the late maturing corn cultivars. Following the development of early and extra-early maturing corn cultivars that mature in 2 to 3 mo, efforts have intensified at national level to promote corn production in the Sudan savannas (Onyibe et al., 2003). However, these cultivars should be planted at optimum dates to fit into the growing calendar.

The choice of planting dates in the Nigerian savannas is arbitrary. Corn is planted when rains are perceived to be persistent and this activity is also influenced by labor availability (Jagtap and Abamu, 2003). Weber et al. (1995) showed that more than 90% of farmers in northern Nigeria take the risk of planting earlier as a strategy to capture a bonus from early crop sales, avoid pest attacks, and increase crop yields through improved nutrient availability associated with the first rains. Norwood (2001) found dryland corn production in western Kansas to be affected by planting date, hybrid maturity, and plant population. In Sudan, Abdel Rahman et al. (2002) reported planting date and cultivar to affect yield and yield components of corn. The perception in northern Nigeria is that corn should be planted with the late June and early July rain so that it can pollinate in August when the rainfall is stable to avoid possible drought stress in September. However, planting during this period carries the risk of intermittent drought and poor crop establishment in the Sudan savanna zone. Moreover, early planting of extra-early maturing corn cultivars results in crop harvest time coinciding with heavy rainfall periods in August and early September. The incidences of ear rot, due to high moisture content, increase at this time of harvest. Farmers in the West African savannas in general prefer their crops to mature in late mid-October when rainfall is less.

Little research had been done to determine the optimum planting date for early and extra-early maturing corn in the Sudan savanna zone. The success of corn production in the Sudan savanna zone depends on timely planting and growing of adaptable cultivars. The objective of this study was to determine the performance of and optimum planting dates for late, early, and extra-early maturing corn cultivars.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Research was conducted in Borno State, Nigeria at the IITA research sites in Azir, (11^o2' N, 12°88' E) and in Damboa (11^o11' N, 12°46' E) in 2006 and 2007. Both Azir and Damboa lie in the Sudan Savanna ecological zone with annual rainfall of 600 to 800 mm. The soil type in both locations is Alfisols formed on Argillaceous sediments (Kwari et al., 1999) with a pH of 6.1, organic matter content of 9.4 g kg^–1 and P content of 2.4 mg kg^–1 in Azir and in Damboa with a pH of 5.9, organic matter content of 8.2 g ka^–1 and P content of 2.1 mg kg^–1. The soil samples were analyzed for texture and chemical composition as described by Mehlich (1984) and Van Reeuwijk (1992). Before the establishment of the trial, the land was under fallow for 5 yr. Land was plowed and ridged using draft animals. The treatment design was a split plot with three replications. Planting date was assigned to main plot and corn cultivars to subplot. Four planting dates (29 June, 13, 21, and 28 July) and three open-pollinated corn cultivars were used in the experiment. In both years, corn cultivars were 95 TZEE-W (an extra-early maturing type, 80 d to maturity), TZE COMP4 C3 (an early-maturing type, 90 d to maturity) and TZB-SR (a widely used late maturing cultivar, 120 d to maturity). Planting distance was 0.75 m between rows and 0.25 m between plants to give a plant population of 53,333 plants ha^–1. Each subplot was arranged in four rows of 5 m length. At planting, fertilizer in the form of NPK was applied at the rate of 40 kg ha^–1 for each nutrient. Top dressing of N fertilizer, in the form of urea, was applied at the rate of 60 kg N ha^–1 5 wk after planting (WAP). Immediately after planting, gramozone (1:1-dimethly-4,4'-bipyridinium dichloride) was applied at the rate of 3 L ha^–1 to control weeds. Manual weeding was done at 2 and 7 WAP to control late emerging weeds.

Days from sowing to 50% pollen shed (anthesis date) and 50% silk extrusion (silking date) were determined using plants in the two middle rows of each plot. Anthesis-silking interval was calculated as the difference between days to silking and anthesis. The total number of plants and ears were counted in each plot at harvest. The number of ears per plant was then calculated as the total number of ears at harvest divided by the total number of plants harvested. During harvest, aboveground biomass was recorded from 15 plants taken from the middle rows. At each biomass harvest, samples were partitioned into leaves, stems, and grains and the components were oven dried at 60°C for 76 h. Total biomass per plant was calculated as the sum of the different parts per plant. Grain yield was recorded from plants of the two middle rows excluding the end plants of each row. Ears harvested from each plot were shelled and the percent grain moisture was determined using a Dickey-John moisture tester (Model 14998, Dickey-John Corporation, Auburn, AL). Grain yield computed from the shelled grain was adjusted to 120 g kg^–1 moisture content. Before shelling, four ears were randomly selected from each plot and the number of kernels per ear was counted. The cobs were shelled and kernels dried separately for determination of 500 kernel grain weight. After counting, the kernels were returned to the bulk of grains of each main plot for grain yield determination.

All data were analyzed using a mixed model procedure of SAS (SAS Institute, 2003) where replication was considered random effect. The LSD at 5% probability level was calculated and used in comparing treatment means. Pearson's correlation coefficient between grain yield and the other traits was also computed using PROC CORR of SAS (SAS Institute, 2003).

	RESULTS

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Climatic Conditions
Mean average monthly maximum and minimum temperatures for 2006 and 2007 are presented in Table 1 . In Azir, the average maximum air temperature was 36.92°C in 2006 and 35.80°C in 2007. Average minimum air temperature was 23.72°C in 2006 and 25.90°C in 2007. In Damboa, the average maximum air temperature was 37.84°C in 2006 and 36.53°C in 2007. Average minimum air temperature was 21.98°C in 2006 and 22.38°C in 2007. The average temperatures in the two locations were optimal for corn growth. In Azir total rainfall was higher in 2007 (1051 mm) than in 2006 (771 mm). In Damboa rainfall was higher in 2006 (894 mm) than in 2007 (843 mm). In both locations, rainfall was poorly distributed in 2007 than 2006 especially during the active growth stage of the corn crop in August and the grain-filling period in September 2007 (Fig 1 ). There was no rain in the last 3 wk of September in Damboa and in the last week of September in Azir. Moreover, rainfall was much less in the third and last week of August 2007 in Azir and in the last week of August 2007 in Damboa than in 2006 during the same periods. (Fig 1). In Azir, there was a dry spell in the second and third week of July 2006, which affected crop establishment for planting done on July 13 (Fig. 1). As shown in Fig. 1, the rains also ceased in September of 2007 in both locations thereby inducing drought stress for the corn crops during the grain-filling period particularly for corn planted in late July.

View larger version (30K): [in this window] [in a new window]   Fig. 1. Weekly rainfall in Azir and Damboa in 2006 and 2007.

Total Dry Matter and Harvest index
In both locations, significant Y x P interactions were detected for dry matter (Table 2). In both years delayed planting beyond 29 June, generally reduced total dry matter in Azir (Table 4). In 2006, planting on 13 July produced corn total dry matter that was significantly lower than planting on 21 and 28 July. In 2007, planting on 29 June produced total dry matter that was significantly higher than those produced by corn planted on 21 and 28 July. In Damboa, delaying planting beyond 29 June, also reduced corn total dry matter. In 2007, total dry matter was similar for planting dates of 13 and 21 July (Table 4). Cultivar differences were only significant in Azir where TZB-SR produced the highest dry matter. Difference in corn dry matter between TZE COMP4 C3 and 95 TZEE-W was not significant.

A three-way interaction among years, planting date, and cultivar occurred for harvest index (HI) in Azir but not in Damboa. In Damboa, HI was influenced by year, planting date, and cultivar (Table 2). In Azir, HI of TZB-SR was reduced significantly when planting was delayed to 28 July in both years (Table 3). The two other cultivars responded differently to delay planting. In 2006, HI of TZE COMP4 C3 increased when corn was planted on 13 July and declined when planting was delayed to 21 or 28 July. The HI of 95 TZEE-W was not significantly different among planting dates in both years. In 2007, HI of TZE COMP4 C3 was significantly lower when planted on 13 July compared to other planting dates (Table 3. In Damboa, HI was significantly higher in 2006 (0.43) than in 2007 (0.39). Delaying planting to 21 and 28 July significantly reduced HI (Table 3). TZB-SR produced the lowest HI while 95 TZEE-W produced the highest HI in Damboa (Table 3).

Yield and Yield Components
In Azir, Y x P and Y x C interactions were detected for corn grain yield. In 2006, significant yield reductions occurred as planting date was delayed in Azir. The highest reduction in grain yield occurred when corn was planted on 13 July (42%). Although grain yield decreased as planting date was delayed in 2007 in Azir, significant reduction in grain yield only occurred when planting was delayed to 28 July (32%) (Table 4). In Azir, grain yield of all cultivars was significantly higher in 2006 than 2007. In 2006, 95 TZEE-W had significantly higher grain yield than TZE COMP4 C3 but not in 2007. The two early- and extra-early maturing cultivars had similar grain yields which were significantly higher than the grain yield of the late maturing cultivar TZB-SR in 2007 (Table 5). Planting date and cultivar influenced grain yield significantly in Damboa (Table 2). In Damboa, grain yield was significantly reduced as corn planting was delayed to 13, 21, and 28 July. The extra-early maturing cultivar, 95 TZEE-W produced grain yield that was significantly higher than the yields of TZE COMP C3 and TZB-SR (Table 5). Grain yield of TZE COMP C3 was also higher than TZB-SR.

In both locations, Y x P interaction was significant for number of kernels per ear. In Azir, Y x C interaction was also significant (Table 2). In Azir, number of kernels per ear was lowest when corn was planted on 13 July in 2006 (Table 4). Other significant reduction was recorded when corn was planted on 28 July (Table 4). In 2007, a significant reduction in the number of kernels per ear was recorded when planting was delayed to 21 and 28 July. In Damboa, number of kernels per ear significantly declined when corn planting was delayed to 28 July in both years. In 2006, differences between planting on 21 and 28 July were significant but differences between planting on 28 and 13 July were not significant. In 2007, delaying planting to 21 and 28 July significantly reduced the number of kernels per plant but differences between planting on 21 and 28 July were not significant (Table 4) In Azir, TZB-SR produced the highest number of kernels per ear in 2006 whereas in 2007 95 TZEE-W had the highest number of kernels per ear (Table 5). Number of kernels per ear was higher in 2006 than 2007 for all cultivars in Azir. In Damboa, TZE COMP4 C3 produced the lowest number of kernels per ear in both years. The magnitude of differences among the cultivars was however higher in 2006 than 2007. In contrast to Azir number of kernels per ear was higher in 2007 than 2006 for all cultivars. Significant P x C interaction was also detected in Damboa for number of kernels per ear. TZB-SR produced the highest number of kernels per ear on all planting dates except on 13 July when 95 TZEE-W produced the highest number of kernels per ear (Fig. 2 ).

View larger version (68K): [in this window] [in a new window]   Fig. 2. Effect of planting date and cultivar on kernel number ear–1 in Damboa. S.E.D = standard error of the difference.

In both locations, Y x P and Y x C interactions were significant for number of ears per plant (Table 2). In Azir, planting on 13 July produced the lowest number of ears per plant in 2006. In 2007, number of ears per plant generally declined with delay in planting. The least number of ears per plant was produced when corn was planted on 28 July (Table 4). Ears per plant were significantly higher in 2006 than 2007 when corn was planted on 21 and 28 July. The cultivars, TZE COMP4 C3 and 95 TZEE-W produced higher number of ears per plant than TZB-SR in 2006. In 2007, TZB-SR produced the lowest number of ears per plant which significantly differed with the number of ears produced by the TZE COMP4 C3 and 95 TZEE-W. The late maturing cultivar TZB-SR had more ears per plant in 2006 than in 2007 (Table 5). Planting date x cultivar interaction was also significant for number of ears per plant in Azir. Number of ears per plant was higher for TZB-SR than the other cultivars when planted on 29 June. This cultivar produced the least number of ears per plant on all other planting dates. Differences in the number of ears per plant on TZE COMP4 C3 and 95 TZEE-W between planting dates were not significant (Fig. 3 ). In Damboa, delaying planting to 21 July significantly reduced the number of ears per plant in 2006 (Table 4). In 2007, significant reductions were only recorded when corn was planted on 28 July. In Damboa, TZB-SR produced the highest number of ears per plant in 2006. Differences among cultivars were not significant in 2007 (Table 5).

View larger version (60K): [in this window] [in a new window]   Fig. 3. Effect of planting date and cultivar on number of ears plant–1 in Azir. S.E.D = standard error of the difference.

	DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

Very high rainfall in August and less in July may also affect crop performance. Typically rainfall in July is 70% of what falls in August in the Sudan savanna zone thereby providing sufficient moisture for crop establishment and development. Sufficient moisture is needed both early in the season and during crop development. Lower moisture in July delays crop development. Delayed planting generally increased days to tasseling and silking and ASI for all cultivars in both years and location. The late-maturing cultivar TZB-SR had higher number of days to tasseling and silking than the early and extra-early maturing corn cultivars in both locations. There were many interactive effects among year, planting date, and cultivar although these effects were not consistent across locations. Days to tasseling and silking consistently increased when planting was delayed to 21 and 28 July in both locations and years. This suggests that delaying planting to these two dates may increase days to flowering with consequent negative effect on grain yield. The late-maturing cultivar TZB-SR generally had the highest number of days to silking than the two earlier maturing cultivars in both locations and years. In 2006, when rainfall was better distributed, days to silking did not significantly differ between the two earlier maturing cultivars. In 2007 when rainfall was poorly distributed, the extra-early maturing cultivar 95 TZEE-W had number of days to silking that was significantly lower than that of the early maturing TZE COMP4 C3. Also ASI was similar among cultivars in Damboa in 2007 when rainfall was poorly distributed. These differences underline the influence of moisture on flowering. Delayed silking and long ASI are indications of environmental stress in maize. The stress can be caused by drought or low soil N status (Kamara et al., 2005; Edmeades et al., 1993; Bänziger and Lafitte, 1997). In this study, the crops were supplied with adequate amounts of nutrients. Therefore the delay in silking and the long ASI may be due to insufficient moisture during the reproductive stage of the crop. This may be particularly true for the late-maturing cultivar. Herero and Johnson (1981) reported a delay in silking in maize under drought stress resulting in decreases in grain yield and kernel number. The shorter ASI recorded for the early and extra-early maturing cultivars in both locations and years indicates that these cultivars were affected less by moisture stress. This may be because they grew faster and flowered earlier before moisture stress set in. Because temperatures are usually optimal during the cropping season, early planting in the season is advisable to avoid late season drought stress during pollination.

The interaction among year, planting date, and cultivar was significant for HI in Azir because of unexpected moisture deficit at the beginning of July in 2006 which severely affected crop establishment. Consequently, delaying planting to 13 July in this location significantly reduced corn dry matter in 2006. In 2007 when rainfall was sufficient for crop establishment in July, delayed planting only reduced corn dry matter when planting was delayed to 21 or 28 July. Delaying planting to 13 July significantly reduced HI of the late maturing cultivar in both years. In 2006, HI was only significantly reduced when planting was delayed to 21 and 28 July for TZECOMP4 C3 and 28 July for 95 TZEE-W. In 2007, 95 TZEE-W produced similar HI across planting dates. At all planting dates, the extra-early maturing cultivar, 95 TZEE-W produced significantly higher HI than the early and late maturing corn cultivars because it flowered and matured earlier than the other cultivars which made it possible to escape the prolonged moisture stress during the later part of the cropping season. This suggests that the reduction in HI is dependent on maturity period of the corn cultivar. Harvest index of the extra-early maturing cultivar was apparently not affected by delayed planting. The influence of planting dates on yield and yield components also varied with year in both locations because of differences in rainfall distribution in the 2 yr. A dry spell in the second and third week of July in Azir in 2006 affected crop establishment and consequently reduced the yield and yield components of corn cultivars planted on 13 July. In 2007, yield and yield components were only reduced when corn planting was delayed to 21 or 28 July in both locations. The reduction in corn dry matter, HI, and yield and yield components when corn was planted on 21 or 28 July may be due to insufficient moisture during the reproductive stage and grain-filling period of the crops. When corn is planted on 21 or 28 July, the earliest period it can flower is sometime in September, a period during which rainfall is considerably low in the Sudan savanna. In this study, rainfall in September was considerably less than in July and August in Azir in both years. In Damboa when rainfall was higher in September than in July in both years, its distribution was very poor with most rain falling in the first 2 wk of September. The poor distribution of rainfall in September may lead to moisture stress thereby delaying flowering as was recorded in this study. Moreover, flowering in September means that grain-filling period will extend to October, a month with little or no rainfall in the dry savannas of northern Nigeria. As reported elsewhere, decreasing moisture availability reduces dry matter accumulation (Kamara et al., 2003; Turner et al., 1986; Novero et al., 1985). The reduction in number of kernels per plant, ears per plant and kernel weight and the high positive correlation of these traits with grain yield corroborate reports elsewhere that these traits are significantly affected during periods of moisture stress (Kamara et al., 2003; Bolanos and Edmeades, 1993, Bolanos et al., 1993). In the current study, delayed planting to 21 or 28 July consistently led to significant reduction in yield and yield components in both locations and years.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Results from this study indicated that the optimum planting date for corn in both locations is the last week of June when the rains begin to stabilize. However, rainfall in the Sudan savannas at the beginning of the cropping season in late June is unpredictable and unstable. Farmers therefore delay planting until first or second week of July when soils reach field capacity, which is suitable for the extra-early maturing cultivar. Harvest index of the extra-early maturing cultivar, 95 TZEE-W, was higher than the other cultivars on all planting dates. Averaged over years, locations, and planting dates, grain yield of 95 TZEE-W was significantly higher than that of the early (TZE COMP4 C3) and the late maturing cultivar (TZB-SR) indicating that extra-early maturing cultivars are the most suited for production in both locations. To reduce risk of drought stress, it is recommended to plant extra-early maturing cultivars in the last week of June or first week of July in the Sudan savanna zone.

	ACKNOWLEDGMENTS

 
We thank the Canadian International Development Agency (CIDA) for funding the project 'Promoting Sustainable Agriculture in Borno State which financed this study and the technical staff at IITA for managing the research fields.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
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