Straw incorporating in shallow soil layer improves field productivity by impacting soil hydrothermal conditions and maize reproductive allocation in semiarid east African Plateau

Ridge-furrow plastic film mulching (RFM) planting system can conserve soil water and boost crop yield in semi-arid rainfed agricultural areas. In the east African Plateau (EAP), the RFM system has shown significant promoting effects on the yield and water use efficiency in maize (Zea mays L.) and wheat (Triticum aestivum L.). Although the RFM system is effective and efficient, it is unclear how to further increase crop productivity under RFM in EAP where soil moisture is limited. This study advocates for an integrated practice (maize straw returning) in the RFM system. Field trials were conducted using maize cultivar DK8031 to investigate the effects of maize straw returning in the shallow soil layer on soil hydrothermal conditions from 2021 to 2022. Maize productivity, water use efficiency, soil organic carbon, and soil total nitrogen were determined under RFM in Kenya, EAP. Three treatments were designed as follows: 1) conventional bare flat planting, CK; 2) RF with full plastic film mulching, RFM; and 3) RFM with maize straw piece (9 t ha⁻¹) returning to 0–30 cm soil layer, RFMR. The results indicated that soil water storage (SWS) was substantially improved by 40.8 mm in 2021 and 30.9 mm in 2022 in RFMR, respectively, than that of CK, which was also significantly greater than that of RFM (p<0.05). Under relatively high air temperature at the silking stage, soil temperature at 15 cm soil depth was averagely reduced by 0.85 °C in RFMR and 0.15 °C in RFM, respectively, compared with CK. Across two growing seasons, grain yield and water use efficiency increased by 470 kg ha⁻¹ and 1.5 kg ha⁻¹mm⁻¹ in RFMR compared to RFM and 2407 kg ha⁻¹ and 7.1 kg ha⁻¹mm⁻¹ compared with CK, respectively., The highest economic benefit was found in RMFR, relative to RFM and CK. The above trend was positively associated with the improvements in hydrothermal conditions in the shallow soil layer. Additionally, soil organic carbon was increased by 0.88 g kg⁻¹ in RFMR relative to CK due to improved soil structure and physiochemical traits. For the first time, we found that straw pieces returning to the shallow soil layer can further boost maize productivity on the basis of RFM, which was intended to improve soil texture in EAP.