In this situation farmers' decision to plant is associated with risks of crop failure. Long dry spells at the beginning, mid and end of the rainy season are also becoming more frequent even in the wetter southern and Northern Guinea savannas (NGS) ( Adnan et al., 2017). Delay in onset of the rainy season leading to total crop failure has been consistently reported in many areas of West and Central Africa ( Graef and Haigis, 2001 Marteau et al., 2011). In most cases farmers usually plant with the first rains in order to capture the flush of soil N that comes with the first rains ( Sachs et al., 2010). Most farmers normally plant maize when the rains are perceived to be persistent and this activity is also influenced by labor availability ( Jagtap and Abamu, 2003). The onset and end of rainy season vary, making it difficult for farmers to take decision about planting ( Odekunle, 2004 Tofa et al., 2020). Uncertainties due to changing weather patterns are making rain-fed agricultural production to become more variable and riskier to farmers. Drought and rainfall variability due to climate change are the major threats to maize production in the Nigeria savannas ( Kamara et al., 2009 Ayanlad et al., 2018). Poor soils ( Jibrin et al., 2012), frequent droughts ( Kamara et al., 2009), and pest and disease ( Badu-Apraku et al., 2009) limit maize production. This is far less than the yield of about 7–8 t ha −1 observed in research fields ( Shehu et al., 2019). Despite the increase in production, maize yields in Nigeria have remained low over the last decades hovering around 1.8–2 t ha −1 ( FAOSTAT, 2018). Significant increase has been witnessed in its production in the past three decades in the savannas of Nigeria, even in the semi-arid Sudan Savanna (SS) zone where rainfall is erratic ( Kamara et al., 2009 FAOSTAT, 2017). Maize ( Zea mays L.) is a principal food security and a major commercial crop in Nigeria providing food, animal feed, and industrial raw materials ( Badu-Apraku et al., 2009). This is probably due to the poor soil fertility in this location.
#PLANTING DENSITY APSIM WINDOWS#
Though Yelwa is in the SGS, lower yields and narrower sowing windows were simulated for both varieties than for those of the other locations. For the medium-maturing variety, IWDC2SynF2, planting should be done by the first week of July. In the Sudan savannah (SS) where the growing season is 90–120 days, planting of 2009EVDT can be delayed up to the third week of July. In the Northern Guinea savannah (NGS) where the length of growing season is 150–180 days, the optimum planting window is June 15–July 19 for both varieties at Zaria and June 8–July EVDT and June 8–August 2 for IWDC2SynF2 at Sabon Gari. The planting window that gives attainable yield at Yelwa, is June 15–July EVDT and June 8–28 for IWDC2SynF2. In the Southern Guinea savanna (SGS) where the length of growing season is 180–210 days, the best planting window was June 8–July EVDT and June 8–July 26 for IWDC2SynF2 in Abuja. Planting from June 15 to 28 simulated the highest mean grain yield for both varieties in all the agro-ecologies. The seasonal planting date analysis showed that optimum planting windows for 2009EVDT and IWDC2SynF2 depend on the variety, agro-ecozones and sites. The evaluation with the experimental data showed that the model performance was reasonable and accurately predict crop phenology, total dry matter (TDM) and grain yield for both maize varieties. The model was run for 11 planting windows starting from June 1 and repeated every 7 days until 16 August using long-term historical weather data from the 7 selected sites representing three agro-ecological zones (AEZs).
#PLANTING DENSITY APSIM SIMULATOR#
The Agricultural Production Systems Simulator (APSIM) model was calibrated and validated and used to identify the optimum planting windows for two contrasting maize varieties for three agro-ecologies in the Nigeria savannas.