Enhancing climate change resilience in sorghum bicolor l. (sorghum) production through sustainable crop intensification

Abstract

Low and poorly distributed rainfall coupled with insufficient nitrogen (N) fertilizer use in rain-fed smallholder farming systems affect Sorghum bicolor L. (sorghum) yields. Contour-based rainwater harvesting (RWH) practices can provide viable adaptative climate change resilient crop intensification practices to overcome rainfall variability due to climate change in semi-arid regions of Zimbabwe. The research aimed to quantify sorghum grain yield response to in-situ water retention techniques (basins, ripper, and tied ridges), and RWH (Tied Contour (TC) and Infiltration Pits (IP)) under different nutrient management practices. A meta-analysis was conducted to determine sorghum grain yield response to in-situ rainwater retention techniques. Using the weighted mean yield difference approach, the in-situ rainwater retention practices were assessed under different rainfall amounts, soil texture, mulch, and nitrogen fertility. The results of the meta-analysis showed that basins, ripper, and tied ridges had no sorghum grain yield advantage over the conventional practice in all agronomic environments. To determine the grain yield performance of sorghum varieties (Macia and Sc Sila) in RWH practices at varying nutrient management practices (inorganic nitrogen fertilizer, inorganic nitrogen fertilizer + organic fertilizer, and organic fertilizer), a field experiment was set up. Experiment 1 was made up of the two sorghum varieties under RWH practices and inorganic nutrient management practice. Experiment 2 was made up of the two sorghum varieties under inorganic nitrogen + organic fertilizer. Experiment 3 consisted Macia and Sc Sila sorghum varieties under RWH practices and organic nitrogen management. In all the three experiments a randomised completed block design experiment in a split-split plot configuration was conducted in 2016/17 to 2018/19 seasons at Mt Zonwe smallholder farming area in Mutare district, Zimbabwe. Nitrogen and rainwater use efficiencies were also evaluated under RWH practices and inorganic nitrogen fertilizer experiments. Soil moisture and grain yield data were subjected to analysis of variance and least significant difference at p<0.05 was used to separate significantly different means. The results revealed that TC and IP increased gravimetric soil water content (gwc). Tied Contour and IP yielded more sorghum grain than modified standard contour (SC) in all the seasons, nitrogen application rates, and distance from RWH. In the contour based RWH and inorganic nitrogen + cattle manure experiment, results showed that the grain yields of Macia and Sc Sila were considerably higher under TC and IP than SC in all the seasons. Macia had a higher grain yield at each incremental level of nitrogen addition to cattle manure than Sc Sila. The findings from the contour based RWH practice and cattle manure experiment showed that sorghum grain yield increased with an increase in cattle manure application up to 20 t/ha and varied in the order TC > IP > SC. Macia showed a higher yield than Sc Sila at all cattle manure application rates. The assessment of agronomic efficiency (AE) and rainwater use efficiency (RUE) under the contour based RWH practices and inorganic nitrogen fertilizer showed that TC and IP increased AE compared with SC across all nitrogen application rates, distances from RWH practice, and seasons. Macia had higher AE than Sc Sila at nitrogen application of 50 and 70 kg/ha while nitrogen application >100 kg/ha had no difference in both varieties. Rainwater use efficiency was 21% greater in Macia than Sc Sila while nitrogen fertilizer application increased RUE up to 100 kg N/ ha beyond which there was no difference. The findings suggest that planting basins, ripper planting, and tied ridges have no yield advantage over conventional farming practices, while TC and IP, inorganic and organic nutrient management practices proved to be resilient crop intensification practices in sorghum production. This was evidenced by improved soil moisture, sorghum grain yield, nitrogen use efficiency, and rainwater productivity in rainfed smallholder farming systems. Keywords; Tied contour, Infiltration pits, basins, tied ridges, ripper planting, nutrient management