Abstract Crop production in Sub-Saharan Africa (SSA) is constrained by rainfall variability and declining soil fertility. This has over time led to a decrease in crop yield, among them also maize. This decrease is also experienced in the sub-humid and semi-arid locations of Kenya. Among the commonly used soil and water management practices in SSA are Conservation Agriculture (CA) and integrated soil fertility management (ISFM). Crop response to these management practices is influenced by the existence of soil fertility gradients which are common among smallholder farmers. This paper presents results from a study done in the sub-humid and semi-arid location of Kenya, focusing on the effects of CA- and/or ISFM-based practices on maize yield. Trials were set out on farms within the two locations using a one farm one replicate randomized design. In each farm, CA-based treatment, no tillage with residue retention (NTR), ISFM-based treatment, conventional tillage with use of manure (CTM), a combination of CA + ISFM, no tillage with residue retention and use of manure (NTRM) and a control, (C) were laid down on fields representing high and low fertility soils. The trials started in the long rains of 2017 (LR2017) running for four seasons i.e., LR2017, short rains 2017 (SR2017), long rains 2018 (LR2018) and short rains 2018 (SR2018). Soil water content (SWC) and nitrogen use efficiency (NUE) were also monitored and evaluated. In either high or low fertility fields, maize grain yield was significantly different between the control and both NTR, CTM and NTRM with no significant differences between NTR, CTM and NTRM. Maize grain yield increase compared to the control was highest under ISFM in the low fertility fields in both locations and all seasons. For example, during the last season, SR2018, NTR, CTM and NTRM significantly increased maize grain yield by 136 %, 297 %, and 208 %, respectively, compared to the control, in the low fertility fields of sub-humid Kibugu. In the semi-arid Machang’a, the increase by NTR, CTM and NTRM, respectively, in the low fertility fields was 146 %, 379 % and 183 % for SR2018. This was linked to the tendency of ISFM to improve crop yield in the short run. For both locations, SWC and NUE were highest under NTR. In the sub-humid Kibugu, during SR2018, at the grain filling stage, 78 days after sowing, SWC under NTR, CTM and NTRM was higher by 16 %, 9 % and 20 %, respectively, compared to the control. Also at 78 days after sowing, in the semi-arid Machang’a, SWC was 18 %, 7 % and 15 % significantly higher under NTR, CTM and NTRM, respectively, compared to the control. The higher SWC observed under NTR and NTRM was related to no tillage with residue retention while under CTM it was related to improved soil organic matter through manure addition. NUE, on the other hand, was 26 % and 23 % in Kibugu and Machang’a, respectively, and lowest under the combined practice (NTRM), i.e., 19 % and 15 % in Kibugu and Machang’a, respectively. The high NUE under CA was attributed to the placement of urea in the planting holes while maintaining residue on the soil surface. The low NUE under NTRM was linked to fertilizer N immobilization. Lastly, from the biomass yield, our study showed that monocrop maize under NTR requires a kick-starting by an ISFM-based practice in the low fertility fields of the semi-arid region.

中文翻译：

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肯尼亚半湿润和半干旱地区结合保护性农业和土壤肥力综合管理的玉米生产

摘要 撒哈拉以南非洲 (SSA) 的作物生产受到降雨量变化和土壤肥力下降的限制。随着时间的推移，这导致作物产量下降，其中包括玉米。肯尼亚的半湿润和半干旱地区也经历了这种减少。SSA 中常用的土壤和水管理实践包括保护性农业 (CA) 和综合土壤肥力管理 (ISFM)。作物对这些管理做法的反应受到土壤肥力梯度的影响，这在小农中很常见。本文介绍了在肯尼亚半湿润和半干旱地区进行的一项研究的结果，重点关注基于 CA 和/或 ISFM 的做法对玉米产量的影响。试验是在两个地点的农场上进行的，使用一个农场一个重复的随机设计。在每个农场，以 CA 为基础的处理、免耕保留残留物 (NTR)、基于 ISFM 的处理、使用粪肥的常规耕作 (CTM)、CA + ISFM 的组合、免耕保留残留物和使用粪肥（ NTRM) 和对照 (C) 被放置在代表高肥力和低肥力土壤的田地上。试验开始于 2017 年的长雨季（LR2017），运行四个季节，即 LR2017、2017 年的短雨季（SR2017）、2018 年的长雨季（LR2018）和 2018 年的短雨季（SR2018）。还监测和评估了土壤含水量 (SWC) 和氮利用效率 (NUE)。在高肥力或低肥力田，玉米籽粒产量在对照与 NTR、CTM 和 NTRM 之间存在显着差异，NTR、CTM 和 NTRM 之间没有显着差异。与对照相比，在 ISFM 下，在两个地点和所有季节的低肥力田中，玉米籽粒产量增加最高。例如，在上一季，在亚湿润基布古低肥力田中，与对照相比，SR2018、NTR、CTM和NTRM分别显着提高了136%、297%和208%的玉米产量。在半干旱马场阿，低肥力田的 NTR、CTM 和 NTRM 的增加分别为 SR2018 的 146%、379% 和 183%。这与 ISFM 在短期内提高作物产量的趋势有关。对于这两个地点，SWC 和 NUE 在 NTR 下最高。在亚湿润基布谷，在 SR2018 期间，在籽粒灌浆阶段，播种后 78 天，NTR、CTM 和 NTRM 下的 SWC 分别比对照高 16%、9% 和 20%。同样在播种后 78 天，在半干旱的马昌阿，与对照相比，在 NTR、CTM 和 NTRM 下 SWC 分别显着高 18%、7% 和 15%。在 NTR 和 NTRM 下观察到的较高 SWC 与免耕保留残留物有关，而在 CTM 下，它与通过添加肥料改善土壤有机质有关。另一方面，基布古和马昌阿的 NUE 分别为 26% 和 23%，在联合实践 (NTRM) 下最低，即基布古和马昌阿分别为 19% 和 15%。CA 下的高 NUE 归因于在种植孔中放置尿素，同时将残留物保持在土壤表面。NTRM 下的低 NUE 与肥料 N 固定有关。最后，从生物质产量来看，