Determination of optimum planting date and growing season of maize in the northern savanna zone of Ghana

Transcription

1 Soil ter Balance in the Sudano-Sdhelian Zone (Proceedings of the Niamey Workshop, February 99). IAHS Publ. no. 99,99. Determination of optimum planting date and growing season of maize in the northern savanna zone of Ghana INTRODUCTION GN. KASEI Soil Research Institute, Nyankpala Agricultural Experiment Station, PO Box, Tantale, Ghana J. J. AFUAKWA Crops Research Institute, Nyankpala Agricultural Experiment Station, PO Box, Tamale, Ghana Abstract The northern savanna zone of Ghana is mostly semiarid. The irregular onset and distribution of the rains in this part of Ghana makes interpretation of agronomic experiments difficult. This report seeks to determine the optimum time of planting of maize (Zea mays L.) in relationship with the length of the growing season in the northern savanna zone of Ghana. By relating climatic data analyses which incorporate soil factors for over years (9-988) to a maize cropping system, the planting times for maize in this area were determined. Results indicated that the growing season varied between 6 to. The best planting time for maize was found to be during the last two weeks of May in order to meet moisture requirements during flowering and growing period lengths. It was possible from these data analyses and the climatic water balance of the area to programme field operations in advance, for both early and late maturing varieties of maize to mature in the moisture availability period of these areas which form part of semiarid Ghana. The delineation of the West African ecologies (Papadakis, 966) shows about one third of the land area of Ghana in the savanna zone. The northern savanna zone of Ghana lies between latitudes 8 and H 'N with a land area of 6 96 km which is mostly semiarid. It comprises the Guinea and Sudan savanna and has an annual precipitation between 9 and mm. Rainfall in the northern savanna zone of Ghana is dependent on the seasonal northward movement of the moisture-laden Inter-Tropical Convergence Zone (ITCZ). The duration of the rainy season at any place depends on the latitudinal position of the ITCZ. About 9% of the rainfall is received between June and September. Rainfall variability is between -% in the Guinea savanna zone and -% in the Sudan savanna zone (Zonneveld, 98). In the Guinea savanna zone, Kasei (988) reported an increase in the 9

2 C. N. Kasei & J. J. Ajuakwa 9 interannual variation of rainfall distribution along the zone. The seasonal characteristics of the monsoon have been reported by Hamilton & Archbold (9), lker (97) and Adejokun (966). In this area rainfed farming under an erratic monomodal rainfall pattern is the dominant practice. Several factors cause poor yields of crops but the major problem contributing to low yields in dryland agriculture is a deficiency of soil water. In the northern savanna zone of Ghana, the time of planting to meet the moisture adequacies of the maize crop has posed a major constraint to farmers resulting in frequent crop failures or reduced yield. Variations in the onset of rains in the savanna area have made it difficult to apply the results of agronomic experiments to determine the exact planting time of maize (NAES, 98, 98; GGDP, 986). However, the need to guarantee the farmer an improvement in both increased yields and yield stability has been a major goal of most national agriculture research programmes. Researchers have analysed rainfall data and used the onset of the rains in suggesting the growing time of maize and other cereals for the bimodal rainfall areas of Kenya (Stewart, 98) and predicting the rainy season potential at the beginning of the rainy season for locations in Niger and Burkina Faso (Sivakumar, 988). Maize is a staple food and cash crop in northern Ghana, and is now a popular cereal virtually replacing the traditional sorghum (Sorghum bicolor) and millet (Pennisetum americanum L.) but there is a wide difference between its production and consumption. This study is aimed at determining the optimum time of planting of maize in relation to the length of the growing season in order to reduce the risk of crop failure in the northern zone of Ghana. METHOD OF AGROOJMATIC DATA ANALYSIS In order to apply meteorological information for the determination of the optimum planting time and the length of the growing season of maize, six locations in northern Ghana were chosen: Nyankpala-Tamale, Damongo, Yendi,, Navrongo and Manga-Bawku (Fig. ). Daily rainfall data for over years (9-988) with missing years taken into consideration, were used in this analysis. Soil factors such as: (a) Rooting depth of maize as measured by Haerdter (989) on an Alfisol (predominant soil type for maize in the area) was between and 6 cm. For the purpose of this paper a rooting depth of cm was used. (b) The water holding capacity (WHC) of the soil (sandy loam) was taken as approximately 6 mm/m for the area. (c) The available water (AW) was computed aa- rooting depth x WHC, and is mm. (d) ter requirement (WR) during flowering was about mm day" taken from calculated potential évapotranspiration (PE) according to Penman's formula (Penman, 98).

3 9 Determination of optimum planting date of maize N s / / / / / / / / Navrongo ////[_ N ^^C / / /v ^^L /J 9 N - 8 N J r W \ Yendi J ( ï ) Tamale Nyankpala / r, / Damongo / I V SUDAN SAVANNA ZONE \ GUINEA SAVANNA ZONE ) W W E Fig. Selected locations for analysis in the northern savanna zone of Ghana. (e) During flowering the available water can, therefore, satisfy the water requirement for a period of 7.. The value 7. was adjusted to to facilitate the use of rainfall totals in decades. Some methods have already been developed for the definition of the onset of rains (Cocheme & Franquin, 967; lter, 967; Benoit, 977; Sivakumar, 988). The criterion used here is that of receiving a total of mm of rain within, after which there is no dry spell longer than seven within the next. The end of the rains is defined when a total of mm within after which no rain falls for the next. The length of the growing season is the difference between the dates of the beginning and ending of rains. The length of the rainy season was also computed from the water balance of two locations, Nyankpala and Navrongo in the Guinea and Sudan savanna zones respectively, using monthly rainfall and estimated évapotranspiration (Penman). Data for the driest -year period ( ) was used to identify the humid periods in order to guarantee the farmer the most probable moisture availability period for maize production in the two locations. RESULTS AND DISCUSSION Although the onset of rains usually occurs by mid May, maize is traditionally planted by most farmers in late June or July in the northern savanna zone, when the rains are assumed to have stabilized. Hence the length of the growing season becomes reduced resulting in yield reduction or total crop failure, depending on the maturity of the maize variety.

4 C. N. Kasei & J. J. Afuakwa 96 The criterion devised here is to use the definition of the onset of the rains (Tables and ) as the date of planting of maize for each year during which period rainfall has stabilized. Table The number of times the computed planting date occurred in each month for selected locations in Ghana (9-988) Location March April May June July August September Nyankpala Yendi Damongo Navrongo Manga Table Occurrence of computed planting date/onset of rains between and May for selected locations in Ghana Location Nyankpala Yendi Damongo Navrongo Manga 7 6* 7 7* 6" 7" 6* 8* 'Planting date (week) for location. The planting of maize computed for the northern savanna zone indicates the month of May (Table ) as the optimum planting time to meet maize crop water requirements. Data on computed planting dates in May (Table ) and the ranges of onset and ending of rains (Table ) for all locations show that the last two weeks of May are optimal. Table Percent occasions of onset of rains in May and the ranges of onset and ending of rains for selected locations in Ghana (9-988) Location % Onset Onset of rains: in May Range Average date Ending of rains: Range Average date Nyankpala Yendi Damongo Navrongo Manga May May May May May May /-/ 9/9-7/ /-/ 9/9-/ /9-/ /9-/ October 8 October October October October October

5 97 Determination of optimum planting date of maize The rainfall pattern in the zone makes the computed date of planting (Table ) advantageous since the rainfall preceding this time results in good soil water conditions for seedling establishment. At Yendi, planting during the second week is favourable. This is also, possible at Damongo (Table ). The data suggest a longer growing season in the Yendi area and this allows for planting early in the rains which is essential for maximum crop production (Akehurst & Sreedharam, 96). Early planting has already been reported by Diehl & Hornetz (98) whose simulations of planting dates for Nyankpala revealed that maize could be planted as early as mid April in 86% of the cases, and in the beginning of May in all cases; but in 8% of the cases optimal conditions are not reached before the end of May. The data in Table suggest a longer moisture availability period for early and late maize varieties in the zone, assuming -8 after planting as the critical period of development. The late varieties mature in in this zone and perform better in the southern part of the zone where there is a higher probability of soil moisture accumulation occurring during the reproductive growth and grain filling periods. The May planting time may also be advantageous because the recharged soil moisture storage may allow the crop to withstand occasional dry spells during the growing season. Length of the growing period analyses are presented in Table for all locations. Comparison of these data with computed rainfall onset dates show a strong relationship between the onset of the rains and the length of the growing season. This observation agrees with work reported elsewhere (Sivakumar, 988). The length of the growing season determined for each location is dependent on the highest number of occurrences on onset for the period The early onset of the rains gives a longer growing season and a delayed onset may mean a shorter season. This is confirmed by the occasions of early onset experienced in the Yendi area in April and May indicating a longer season while in Navrongo the onset of rain in May results in a shorter season (Table ). The length of the growing season for each location (Table ) is related to the onset and termination of the rains (Tables and ). In the Nyankpala-Tamale area, the length of the growing season is at least 6- in out of years and -7 in 7 years out of (Table ). In the Yendi area a longer growing season of - Table Number of years with indicated length of growing season (LGS) for selected locations in Ghana (9-988) Location Total in yaers Nyankpala Yendi Damongo Navrongo Manga

6 C. N. Kasei & J. J. Afuakwa 98 is most common indicating adequate soil moisture availability to support long duration crops. In the Damongo area, a growing season of 6-7 is more probable. The Guinea savanna locations (Fig. ) have a longer growing season (Table ) than the Sudanian savanna. This means that maize cultivars of shorter and medium duration may be suitable for the Sudan zone. The water balance after Cocheme (968) for two representative locations (Figs and ) n Post rainy + residual moisture Jan Feb Mar Apr,May Jun Jly Aug Sep Oct Nov Dec i I ^ Maize crop -' i~- Average growing season i Fig. Mean monthly rainfall (o-o) and potential évapotranspiration ( ) at Nyankpala, Ghana (data base: ). n Post rainy + residual moisture - w vi, -b o Jan Feb Mar Apr May Jun Jly Aug Sep Oct Nov Dec I i l >- Maize crop H I i r Average growing season-n Fig. Mean monthly rainfall (o-o) and potential évapotranspiration ( ; at Navrongo, Ghana (data base: ).

7 99 Determination of optimum planting date of maize in the Guinea and Sudanian savanna zones (Fig. ) confirms that it is safe to use the longer maturity variety for the Guinea savanna zone. The moisture balance (Figs and ) enables the farmer to programme field operations and take decisions for crops, particularly maize, in advance for the two representative locations. CONCLUSION Analyses of rainfall data between 9 and 988 indicate that the best time for planting maize in the northern savanna zone is during the last two weeks of May in order to meet the moisture requirements during flowering and the growing season length. The May planting favours the maize crop since a substantial portion of the rains for the season will fall during the growing period until maturity. The length of the growing season is also adequate to support the maize crop at all the locations for the determined time of planting. A positive moisture balance exists during the growing season. It is necessary to evaluate these findings with agronomic experiments. REFERENCES Adejokun, J. A. (966) A dimensional study of the I.T.D. Tech. Note no., Met. Dept, Lagos. Akehurst, B. D. & Sreedharam, K. (96) "Time of planting" A brief review of experimental work in Tanganyika. Agric. For. J., 8-. Benoit, P. (977) The start of the growing season in northern Nigeria. Agric. Met. 8, Cocheme, J. (968) Agroclimatology methods. In: Proceedings of the Reading Symposium, -8. UNESCO, Paris. Cocheme, J. & Franquin, P. (967) A study of the agroclimatology of the semi-arid areas south of the Sahara in West Africa. FAO/UNESCO/WMO Interagency Project on Agroclimatology, FAO, Rome. Diehl, L. & Hornetz, B. (98) Estimation of the probabilities of yield depressions due to the risk of drought and their implications for planting decisions. Nyankpala Agricultural Experiment Station, Annual Report 98 A, GGDP (986) Ghana Grains Development Project Annual Report 986. Hamilton, R. A. & Archbold, J. W. (9) Meteorology of Nigeria and adjacent territory. Quart. J. Roy. Met. Soc., -6. Haerdter, R. (989) Utilization of nitrogen and phosphorus by intercropping and sole cropping systems of maize (Zea mays L.) and cowpea (Vigna unguiculata L.) on an Alfisol in northern Ghana. Nyankpala Agricultural Experiment Station, Agricultural Research Report 989, -. Kasei, C. N. (988) The physical environment of semi-arid Ghana. In: Challenges in Dryland Agriculture - A Global Perspective (ed. by P. W. Unger, T. V. Sneed, W. R. Jordan & R. Jensen), -. Texas Agricultural Experiment Station, Amarillo/Bushland, Texas, USA, August 988. NAES (98) Nyankpala Agricultural Experiment Station, Annual Report 98. NAES (98) Nyankpala Agricultural Experiment Station, Annual Report 98. Papadakis, J. (966) Crop Ecology Survey in West Africa, vol., -7. FAO, Rome. Penman, H. L. (98) Natural evaporation from open water, bare soil and grass. Proc. Roy. Soc. A9, -. Sivakumar, M. V. K. (988) Predicting rainy season potential from the onset of rains in southern Sahelian and Sudanian climatic zones of West Africa. Agric. For. Met., 9-. Stewart, J. I. (98) ter requirements and water use of crops. In: International Conference on African Agricultural Development Technology, Ecology and Society (California State

8 C. N. Kasei & J. J. Afuakwa 6 Polytechnic Univ., USA). lker, H. O. (97) Weather and climate of Ghana. Ghana Met. Dept Note no.. lter, M. W. (967) Length of the rainy season in Nigeria. Nigerian Geogr. J.,. Zonneveld, I. S. (98) Some consequences of mutual relationship between climate and vegetation in the Sahel, Sudan. ITC Journal, -96. International Training Center (ITC), Institute for Aerial Survey and Earth Sciences, The Netherlands.