This study is the first of its kind to quantify possible effects of climate change on rice production in Africa. We simulated impacts on rice in irrigated systems (dry season and wet season) and rainfed systems (upland and lowland). We simulated the use of rice varieties with a higher temperature sum as adaptation option. We simulated rice yields for 4 RCP climate change scenarios and identified causes of yield declines. Without adaptation, shortening of the growing period due to higher temperatures had a negative impact on yields (−24% in RCP 8.5 in 2070 compared with the baseline year 2000). With varieties that have a high temperature sum, the length of the growing period would remain the same as under the baseline conditions. With this adaptation option rainfed rice yields would increase slightly (+8%) but they remain subject to water availability constraints. Irrigated rice yields in East Africa would increase (+25%) due to more favourable temperatures and due to CO2 fertilization. Wet season irrigated rice yields in West Africa were projected to change by −21% or +7% (without/with adaptation). Without adaptation irrigated rice yields in West Africa in the dry season would decrease by −45% with adaptation they would decrease significantly less (−15%). The main cause of this decline was reduced photosynthesis at extremely high temperatures. Simulated heat sterility hardly increased and was not found a major cause for yield decline. The implications for these findings are as follows. For East Africa to benefit from climate change, improved water and nutrient management will be needed to benefit fully from the more favourable temperatures and increased CO2 concentrations. For West Africa, more research is needed on photosynthesis processes at extreme temperatures and on adaptation options such as shifting sowing dates.

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Impacts of climate change on rice production in Africa and causes of simulated yield changes

This study investigates whether coupling crop modeling and machine learning (ML) improves corn yield predictions in the US Corn Belt. The main objectives are to explore whether a hybrid approach (crop modeling + ML) would result in better predictions, investigate which combinations of hybrid models provide the most accurate predictions, and determine the features from the crop modeling that are most effective to be integrated with ML for corn yield prediction. Five ML models (linear regression, LASSO, LightGBM, random forest, and XGBoost) and six ensemble models have been designed to address the research question. The results suggest that adding simulation crop model variables (APSIM) as input features to ML models can decrease yield prediction root mean squared error (RMSE) from 7 to 20%. Furthermore, we investigated partial inclusion of APSIM features in the ML prediction models and we found soil moisture related APSIM variables are most influential on the ML predictions followed by crop-related and phenology-related variables. Finally, based on feature importance measure, it has been observed that simulated APSIM average drought stress and average water table depth during the growing season are the most important APSIM inputs to ML. This result indicates that weather information alone is not sufficient and ML models need more hydrological inputs to make improved yield predictions.

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Coupling machine learning and crop modeling improves crop yield prediction in the US Corn Belt.

Climate change impact on yields and water use of wheat and maize in the North China Plain under future climate change scenarios

This study investigates whether coupling crop modeling and machine learning (ML) improves corn yield predictions in the US Corn Belt. The main objectives are to explore whether a hybrid approach (crop modeling + ML) would result in better predictions, investigate which combinations of hybrid models provide the most accurate predictions and determine the features from the crop modeling that are most effective to be integrated with ML for corn yield prediction. Five ML models and six ensemble models have been designed to address the research question. The results suggest that adding simulation crop model variables (APSIM) as input features to ML models can make a significant difference in the performance of ML models, and it can boost ML performance by up to 29%. Furthermore, we investigated partial inclusion of APSIM features in the ML prediction models, and we found that soil and weather-related APSIM variables are most influential on the ML predictions followed by crop-related and phenology-related variables. Finally, based on feature importance measure, it has been observed that simulated APSIM average drought stress and average water table depth during the growing season are the most important APSIM inputs to ML. This result indicates that weather information alone is not sufficient, and ML models need more hydrological inputs to make improved yield predictions.

/pdf/coupling-machine-learning-and-crop-modeling-improves-crop-5ftxxs3ubv.pdf

Coupling Machine Learning and Crop Modeling Improves Crop Yield Prediction in the US Corn Belt

Remote sensing offers a low-cost method for developing spatially continuous crop production statistics across large areas and through time. Nevertheless, it has been difficult to characterize the production of individual smallholder farms, given that the land-holding size in most areas of South Asia (<2 ha) is smaller than the spatial resolution of most freely available satellite imagery, like Landsat and MODIS. In addition, existing methods to map yield require field-level data to develop and parameterize predictive algorithms that translate satellite vegetation indices to yield, yet these data are costly or difficult to obtain in many smallholder systems. To overcome these challenges, this study explores two issues. First, we employ new high spatial (2 m) and temporal (bi-weekly) resolution micro-satellite SkySat data to map sowing dates and yields of smallholder wheat fields in Bihar, India in the 2014–2015 and 2015–2016 growing seasons. Second, we compare how well we predict sowing date and yield when using ground data, like crop cuts and self-reports, versus using crop models, which require no on-the-ground data, to develop and parameterize prediction models. Overall, sow dates were predicted well (R2 = 0.41 in 2014–2015 and R2 = 0.62 in 2015–2016), particularly when using models that were parameterized using self-report sow dates collected close to the time of planting and when using imagery that spanned the entire growing season. We were also able to map yields fairly well (R2 = 0.27 in 2014–2015 and R2 = 0.33 in 2015–2016), with crop cut parameterized models resulting in the highest accuracies. While less accurate, we were able to capture the large range in sow dates and yields across farms when using models parameterized with crop model data and these estimates were able to detect known relationships between management factors (e.g., sow date, fertilizer, and irrigation) and yield. While these results are specific to our study site in India, it is likely that the methods employed and the lessons learned are applicable to smallholder systems more generally across the globe. This is of particular interest given that similar high spatio-temporal resolution micro-satellite data will become increasingly available in the coming years.

Mapping Smallholder Wheat Yields and Sowing Dates Using Micro-Satellite Data

Evaluation of the APSIM model in cropping systems of Asia

The present study was carried out to study the variation, broad-sense heritability, and genetic advance, correlation among traits for growth, yield, and its attributing traits in lentil genotypes. Sixty lentil genotypes were evaluated in augmented design in 2020 at Khajura, Banke. The results indicated that the genotypes were significantly different for days to flowering, days to maturity, 500 seed weight and grain yield kg/ha. The phenotypic coefficient of variation (PCV) was greater than the genotypic coefficient of variance (GCV) for all traits. The 500 seed weight showed the highest PCV (22%) and GCV (21%) whereas days to maturity showed the lowest PCV (5.5%) and GCV (3.2%). The highest value (90%) of heritability (broad sense) was in and lowest (3%) in pods per plant. Genetic Advance Mean 40% was the highest for seed weight but lowest at 1.2% in pods per plant. Grain yield showed a positive and significant correlation in genotypic level with days to maturity (r = 0.7**), plant height (r = 1.66*), pods per plant (r = 1.15**) and seed weight (r = 0.56*). Path analysis found that the seed weight had the most impact on grain yield followed by pod per plant. Thus, selection for yield in lentils through these characteristics would be effective in the varietal developmental program. 
 

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R. Darai

Papers

Evaluation of the APSIM model in cropping systems of Asia

Genetic variability, heritability and genetic advance in Lentil (Lens culinaris Medik.)