3.3.2. Yield Variations between Flat and Tied Ridge Cultivations

Tied ridges increased the yields more than flat cultivation and nearly doubled the yields in both seasons (Table 5). The reason for this difference could be due to the tied ridge's ability to prolong soil moisture during the crop growth period, improving the efficiency of rain water usage. However, tied ridge cultivation also increased the yield variations among farmers. We found high yield spatial variability for both SES1 (CV = 40.2%) and SES2 (CV = 44.7%) for tied ridges, which differed from SES1 (CV = 30.59%) and SES2 (CV = 18.7%) under flat cultivation (Table 5). The variations in both seasons were significantly different under tied ridges, but the variations did not differ under flat cultivation (Table 5). This difference may imply that for different soils, tied ridges have a variable advantage in terms of improving pearl millet yield. This difference may also indicate that the ability of the tied ridges to prolong soil moisture affected other factors, such as soil fertility level variations, field slopes, previous crops, and organic matter in the scattered plots, all of which support crop growth differently.


**4.**Comparisonofyieldvariationaccordingtosoils.

Note: Statistically significant at 0.05 level is denoted by a star (\*).

### **4. Discussion**

Poor and erratic rainfall is challenging rainfed agricultural production in semiarid areas, such that farmers may experience total harvest loss [12]. From our analysis, we found that rainfall can vary significantly in both space and time within a small area between neighboring fields, which agrees with the results reported by other studies [12,28,29]. The variations can be significantly different within a small area (1500 ha study area) in terms of events, rainfall amount per event, total seasonal rainfall amount, and onset and cessation dates. When the total number of seasonal rainfall events is low, the chance of having a lower seasonal rainfall amount and poor distribution is high and vice versa, as we observed during both seasons. Other studies indicated the potential effects of extreme floods and drought events [18]. For instance, few high rainfall events may result in high total seasonal rainfall amounts with poor distribution (during the seasonal crop growth period). In this study, the numbers of events were highly correlated with the seasonal rainfall amount, and the two seasons of data showed significant temporal variability. This situation is common in semiarid areas [18,20]. For both seasons, the spatial distribution of rainfall per event varied significantly within the area. The variation increased with poor total seasonal rainfall, and increased with a nonsignificant linear trend with a distance among rain gauges in the area. Other studies, such as Gao et al. [30], found that the rainfall spatial variation was obvious during the winter dry season. Graef and Haigis [12] reported that the variations along two different transects in Sahel were nearly equal, and the mean differences in the variations increased with the distance between gauges (from ±1.8 mm at 1 km, ±3.5 mm at 2 km, to ±5.7 mm at 3.2 km). The variability increase with distance may be inconsistent when larger areas are considered due to the inherently high local spatial variability behavior of rainfall [30]. In our findings, the correlation coefficient between spatial rainfall differences was found to be weak, which justifies the tendency for examination on larger scales. Buytaert et al. also found that rain gauges separated at a distance of less than 4 km were highly correlated despite having high spatial variability in average rainfall [29].

The rainfall variability directly impacted the farmer's seasonal pearl millet yield. The collected yield discrepancies from different spatial plots within the study area indicate that field scattering is an effective strategy for reducing the probability of total seasonal harvest loss. Previous case studies from the Sahel region show that scattered fields reduce the yield disparity while enhancing the stability of pearl millet yield between households [12,31]. A similar conclusion can be drawn in this study. Thus, a farmer with scattered fields across the study area has a good chance of stable seasonal crop harvest than the one who has all fields concentrated in the same area. The strategy promotes the spatially efficient use of rainfall. For areas with high variations in soil properties, the choice of locations of the scattered fields should consider the quality of soil to reduce the risk associated with soil. Although, in this study the scattered fields in the area were mostly located on soils with similar properties spatially (HA soils), this is not expected to be the case for many areas. There are findings suggesting that yields are poor on gravelly soils and two to three times greater on clay soils [22]. Another study recorded higher yields on under clay soils than sandy soils [32]. However, from the study that checked spatial variability pattern of yields and soils in a 1 ha field, the authors found that soil variables explained 30% of the total yield variation of pearl millet [33]. Thus, to produce higher yields, proper management is required especially in sandy soils. The soil analysis in the Idifu area indicated that the soil has a higher sand content [26] which means creates a risk of lower yields. In addition to the careful selection of soil for the scattered fields practice, overall good crop management is recommended to improve yields of pearl millet.

The yield was consistently correlated with both the rainfall amounts and the number of events in a season. However, if the crop water requirement is met in timing and amount, other factors, such as soil and crop management, may be the risk sources. In most cases, yield would vary depending on soil properties [34–36]; however, we found no statistical evidence of yield variability for different soils in this study site, possibly due to the insignificant effect of soil interactions with other climatic variables. As established by a previous study, the farmers' soils in Idifu matched in terms of classification and fertility but were noticeably different in terms of texture with predominantly higher sand content [26]. Other studies found yield discrepancies even at the within-field scale, as some parts of the field may

produce more of a crop relative to the rest of the field, indicating microscale interactions between climate, soil, topography, and management [21]. Generally, soils with higher content of swelling clay and silt better retain and release soil moisture; therefore, under adverse limited rainfall conditions, these properties provide a buffer to crop production [37]. Previous studies suggest that the effect of tied ridges is much more pronounced under limited rainfall in high clay content soils than in sandy soils [37]. In wetter seasons, tied ridges have limited advantages in crop production under clay soils especially when rainfall exceeds its retention capacity. The provision of drainage is important under clay soils. Conversely, sandy soils possess good drainage properties, which make tied ridges useful in dry season and less destructive in wetter seasons.

In contrast, tied ridge cultivation increased the pearl millet yield significantly more than the flat cultivation by prolonging soil moisture from harvested rainfall. Therefore, farmers should use this in situ rainwater harvesting (tied ridges) method in their scattered fields to reduce harvest losses and to manage the high rainfall variability. Elsewhere in semiarid areas, the practice has been successful for other cereals, such as maize [38–40] and sorghum [2,39]. However, in our study, we found that tied ridges increased spatial yield variability. While yield varied in both flat and tied ridge management situations, the CV of the tied ridges was higher. Further studies on the interactions among plants, soil, terrain, and climatic factors should focus on combining management strategies, such as the use of field scattering with tied ridges and fertilization, to increase yields and reduce spatial yield variability. Field scattering according to different soil types may also be a solution to manage yield variability but is often limited by the number and distance of farmers' fields or the types and features of existing soils. Farmers can retain the advantage of not losing the entire harvest if these farmers scatter their fields randomly or purposely within their area. We consider the exploration of the effects of certain factors, such as variable planting dates, to be important. For instance, the variable onset and secession dates have implications for a farmer's decision about when to plant [18]. A modelling study performed in the region on maize production suggested that farmers should better fine-tune the dates that are more likely to enhance crop yield [41]. Similar studies for pearl millet may assist in identifying the best planting dates for achieving the best potential yield.
