Maize yield prediction using seasonal weather forecasts and a crop growth simulation model.

Abstract

Maize production in marginal tropical regions is at great risk from rainfall variability. Farmers

would benefit from the ability to forecast production likelihood. In this study we sought to

develop a simple maize production decision support tool for Masvingo by using seasonal

weather forecasts and a crop production model to forecast maize yields prior to the season.

Downscaled ENSO-based statistical seasonal forecasts from RAINMAN were tested against

those downscaled from a Global Circulation Model (GCM) using Climate Predictability Tool

(CPT). RAINMAN was found to perform better at forecasting total seasonal rainfall than CPT.

RAINMAN predictions were 69 % correct in all rainfall categories for the 1991/92 - 2006/07

seasons as opposed to 44 % for CPT (p< 0.05). RAINMAN had a higher hit rate than CPT and

was not biased to any rainfall category while CPT was biased towards the normal and

dry/below normal rainfall categories. Monthly rainfall predictions by RAINMAN were

validated. The tool explained 65 % to 81 % (p<0.05) of the rainfall variability of the

agricultural season (October to April), except for December and March where it explained 37

% and 48 % of the variability, respectively. We generated monthly weather series for the five

phases of the Southern Oscillation Index (SOI). These formed the climatic scenarios used to

run the crop production model (AquaCrop).

Simulated agrometeorological scenarios included three planting dates, optimal and poor

fertility levels, and three maize cultivars. Simulated maize yields ranged from 1.2 t/ha to 5.9

t/ha. Average yields were low for poor fertility levels. 100-day (early maturing) maize cultivars

produced better yields under poor fertility levels. 140-day (late maturing) maize cultivars

attained highest yields (5.9 t/ha) for good rain conditions (neutral, rising, and positive SOI and

(20 %) probability of rainfall occurrence) and minimum yields (1.2 t/ha) under poor fertility.

100-day and 140-day maize cultivars produced higher yields when planted late (7 December).

125-day cultivars produced better yields when planted early (29 October) or on the medium

planting date (16 November). The variance in yields under the given agrometeorological

scenarios point towards the importance of considering maize cultivar and planting date

selection. It was clear that maize production at Masvingo should preferably be done under good

fertility.