Introduction

Rainfall variability, extreme weather conditions, soil and nutrient losses in semi-arid areas are major limiting factors to crop production (Liu and Jin 2017). In addition to soil erosion, rain-fed agricultural production in semi-arid areas is constrained by declining plant water availability and poor soil fertility (Hakl et al. 2017; Li et al. 2020). This suggests the need for more sustainable and resilient techniques that improve soil water conservation and availability for crop production to meet global food demands. Evidence showed that increasing crop yield amidst environmental challenges such as climate change and soil degradation requires the adoption of smart and resilient agronomic practices. For example, by shifting from the traditional single farming technique, which has proven to be less effective and unsustainable (Durán-lara et al. 2020) to more robust agronomic practices like integrated farming methods. For rain-fed agriculture, an integrated approach that combines ridge and furrow rainwater harvesting with multiple mulch materials which considers productivity, economic, energy and environmental sustainability is necessary to address challenges associated with rain-fed agriculture such as crop water stress and soil erosion (Bhatt et al. 2021). Adoption of ridge-furrow rainwater harvesting techniques (RFRH) has been touted as an ideal technique for improving soil fertility and increasing crop yield in semi-arid areas (Bhatt et al. 2021).

Ridge-furrow rainwater harvesting technique involves concentration, collection, storage, and distribution of water that would have naturally exited a landscape through processes such as run-off and evaporation (Rango and Havst 2011). Longstanding evidence indicates that in semi-arid areas, adoption of RFRH on fields increased soil water and crop yield (Baig et al. 2013; Yin et al. 2015; Siderius et al. 2016; Mo et al. 2017). In recent years, farmers have used ridge-furrow mulching to improve the quality of agricultural soils by covering soil surface with various types of materials (Haapala et al. 2014). In northern China, straw mulches and plastic film have been used to improve crop yield (Zhu et al. 2018).

Mulches are essentially used to prevent soil water loss, improve soil water infiltration, and control soil erosion, particularly in arid and semi-arid regions (Mohammadi et al. 2012; Bhardwaj 2013). Mulched soils, especially on-ridge planting, improved soil fertility and microbial biomass than conventional flat planting with no mulch (Zhang et al. 2018). This could be attributed to the decomposition of the mulch (organic) material, moisture conservation and increase soil temperature under mulch compared to no mulch conditions (Moreno and Moreno 2008). Although, the effectiveness of single mulch in reducing runoff and water erosion have been widely reported, studies synthesizing evidence of co-application of mulch with ridge and furrow rainwater harvesting (RFRH + M) and modalities for improving crop yield are lacking. As mulching is an expensive agronomic practice for farmers, a meta-analysis of the impact of mulching with RFRH on soil properties and crop yield is necessary to establish scientific evidence to guide soil management practices and improve food production in semi-arid areas (Jafari et al. 2012). The objective of this MA was to assess the whether the integration of ridge and furrow rainwater harvesting systems (RFRHs) with soil amendments, namely biochar or mulches affect crop yield and soil properties relative to traditional no-till flat planting. Main crops investigated were maize, potato and wheat whereas mulch materials were plastic and straw in addition to biochar amendment. In addition, the MA investigated how factors such as such as precipitation moderate the performance of RFRHs with soil amendments in different regions in China was investigated.

Materials and methods

Scope of peer-reviewed papers

Different online databases (Google Scholar, Science Direct, Scopus (Elsevier), PubMed, JSTOR, and Web of Science) were explored for peer-reviewed articles published in English from 2000 to 2021 that investigated effects of RFRH and mulching on crops (Mak-Mensah et al. 2021a, b). The use of multiple academic databases ensured that selection bias was reduced.

Literature selection criteria and screening

The keywords used in the literature search for the meta-analysis (MA) were: “mulching”, and/or “rainwater harvesting”, and/or “yield” and/or “ridge and furrow”. This yielded 121 articles, which were screened using the following inclusion criteria: (i) the experiment was conducted in a semi-arid region; (ii) field trials with at least ridge and furrow, plastic film mulched ridge, biochar or straw mulched furrow, compared with flat planting treatments (Fig. 1); (iii) mulched ridge and furrow; and flat planting plots were established within the same ecosystem and had similar environmental characteristics at the start of the study; (iv) data on maize, wheat or potato yield was reported; and (v) the experimental duration was clearly specified and the experiment was repeated, at least, two growing seasons.

Fig. 1
figure 1

Flowchart of literature identification, and screening for use in this study. Adapted from PRISMA (Moher et al. 2009)

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We considered and extracted latitude, longitude, elevation, mean annual precipitation, soil organic carbon (SOC)/soil organic matter (SOM), texture, bulk density, and soil physico-chemical properties. The crops (maize, wheat and potato) in the various locations (Gansu, Shanxi, Shaanxi, Ningxia and Inner Mongolia) considered in this review were obtained using the stated inclusion and exclusion screening criteria. After the screening process, 42 articles were retained for the MA (Table 1). A flowchart depicting the screening procedure of articles, which was modified from the PRISMA guideline for meta-analysis (Moher et al. 2009) is shown in Fig. 2.

Table 1 Overview of literature showing location of studies, included in the meta-analysis
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Fig. 2
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Effects of mulching and no mulching in semi-arid areas

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Statistical analyses

The Newcastle Ottawa Scale (NOS) was used to determine the importance of articles examined in this MA (Zeng et al. 2015). High-quality articles were graded on a seven-point scale (papers). On a scale of one to ten, NOS scores ranged from six to nine (Table 1). Because additional detailed measurements have larger impact on overall sample (Yu et al. 2018), research articles with additional detailed measurements were assigned higher weight. Using SigmaPlot (version 14.0), descriptive statistics such as standard deviation (SD), mean, minimum, and maximum values of variables investigated (temperature, precipitation, available nitrogen, available phosphorus, available potassium, bulk density, SOC/SOM, total nitrogen, total phosphorus, total potassium, pH, soil texture, pan-evaporation, field capacity, permanent wilting point, sunshine hours and frost-free period) were computed. Subsequently, MA based on the response-ratio approach was conducted with a construction confidence interval analysis using the random-effect model of Nordic Cochrane Centre's Review Manager Software (Mak-Mensah et al. 2021a). In this MA, effect size was calculated as natural log (ln) of the response ratio (R), which is the ratio of mean crop yield in mulched ridges and furrows plots to mean crop yield in flat planting plots (Eze et al. 2018; Mak-Mensah et al. 2021b).

$$R = \theta_{t} /\theta_{c} ,$$
(1)
$${\text{Effect}}\,{\text{size}} = {\text{In}}R = {\text{In}}\left( {\theta_{{\text{t}}} /\theta_{{\text{c}}} } \right) = {\text{In}}\theta_{t} - {\text{In}}\theta_{c} ,$$
(2)

where θt is the mean crop yield of the ridge and furrow, and θc is the mean crop yield of the flat planting. Yield percentage effect size change (Z) was calculated to further substantiate outcomes from the MA (Eze et al. 2018; Mak-Mensah et al. 2021b):

$$Z = \left( {\exp \left( {\ln R} \right) - 1} \right) \times 100\% ,$$
(3)

A positive percentage value indicated that the ridge and furrow treatment resulted in an increase in the metric of interest compared to the flat planting, while a negative percentage value showed that the ridge and furrow treatment resulted in a decrease compared to the flat planting. Following that, sample sizes, means and SDs for the ridge and furrow, and the flat planting variables were computed using the equation (Mak-Mensah et al. 2021a):

$${\text{SD}} = {\text{SE}} \times \surd n,$$
(4)

For studies that did not report SD, average coefficient of variation (CV) was calculated from the screened data and then the SD was estimated using the equation (Gu et al. 2020):

$${\text{SD}} = {\text{CV}} \times \theta ,$$
(5)

where θ is the mean value of ridge and furrow planting or flat planting with or without mulching. The Nordic Cochrane Centre's Review Manager Software package (RevMan; version. 5.3, Denmark) was used to implement random-effects models to derive effect sizes of ridge and furrow treatment and flat planting with or without mulching for crop yields. Chi-square (χ2) and I2 tests were performed to determine heterogeneity between studies (Tables 2, 3, 4, 5 and 6). I2 < 25% indicates low heterogeneity, 25–75% indicates medium heterogeneity, and I2 > 75% indicates high heterogeneity (Higgins 2003; Huedo-Medina et al. 2006; Mak-Mensah et al. 2021b). The mean differences between ridge and furrow systems with biochar or mulches and flat planting were considered based on their standard errors, sample sizes, and confidence intervals (CI) which were calculated as continuous variables using weighted effect sizes. The 95% CIs for the effect size of a treatment were deemed significant if its CIs did not include zero. Similarly, a treatment was not significant when the 95% CIs included zero. The effect sizes (Odds ratio) frequency distribution was computed in Excel 2019 spreadsheet to validate distribution symmetries of individual studies.

Table 2 Heterogeneity analysis on crop yield in ridge-furrow rainwater harvesting system with mulching using random-effects models
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Table 3 Heterogeneity analysis on crop yield in plastic film mulched ridges compared to flat planting using random-effects models
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Table 4 Heterogeneity analysis on crop yield in straw mulching compared with flat planting using random-effects models
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Table 5 Heterogeneity analysis on crop yield in biochar amendment compared with flat planting using random-effects models
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Table 6 Heterogeneity analysis on crop yield in plastic film with straw compared to flat planting using random-effects models
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Results

Influence of bare ridge-furrow rainwater harvesting system on soil properties and maize yield

Bare ridge-furrow significantly improved soil available potassium (51.55%; p = 0.04) at > 100 mg kg−1 quantity with effect size of 1139.66 and the 95% confidence intervals ranging from 50.42 to 2228.90 compared to the flat planting. Results showed that the effect of bare ridge-furrow rainwater harvesting on soil potassium content was moderated by precipitation amount. Thus, it was found that increase in soil available potassium was significant (p = 0.01) in areas with precipitation higher than 500 mm. Twenty of the studies included in the MA reported that areas with precipitation higher than 500 mm had an effect size of 1058.03 and 95% confidence intervals ranging from 234.50 to 1881.56. I2 test performed indicated low heterogeneity between studies (Table 2). Maize yields in Shaanxi ranged from 19,043.50 to 30,188.10 kg ha−1 in bare ridge-furrow treatment compared to the flat planting which ranged from 353 to 29,582.55 kg ha−1. This indicates 33.10% increase in maize yield for the bare ridge-furrow as compared with the flat planting treatment in Shaanxi. On the contrary, potato and wheat yields in Gansu province did not significantly differ (p = 0.48) between the bare ridge-furrow rainwater harvesting system and the flat planting.

Influence of biochar amended ridge-furrow rainwater harvesting system on soil properties and maize yield

Results from this MA showed that biochar increased available potassium (24.26%) at < 100 mg kg−1, SOC (39.10%) at > 10 g kg−1, total potassium (17.61%) at > 10 g kg−1 and in alkaline soils (4.99%; pH > 7–8). Consequently, the responses of yield to biochar amended ridge-furrow treatments from four study observations in the MA averaged 7600.71 kg ha−1 with an effect size of 905.03 (Fig. 3). The 95% confidence intervals ranged from 414.73 to 1395.32 compared with the flat planting. However, there was no significant difference in maize yield (p > 0.05) with biochar amendment ridge-furrow compared to the flat planting. Also, there was no moderating effect of precipitation and soil properties, namely soil organic carbon (SOC), available nitrogen and phosphorus, total phosphorus, and total nitrogen maize yield. The I2 test indicated no heterogeneity between the studies considered in this MA (Table 5).

Fig. 3
figure 3

Common ridge-furrow rainwater harvesting with mulching practices in semi-arid areas

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Influence of plastic film mulched ridge-furrow on soil properties and potato and maize yield

Soil bulk density increased with plastic film mulch application by 37.11% compared to the flat planting (Fig. 3). In addition, compared to flat planting, total phosphorus, SOC, total nitrogen, and total potassium for the plastic film mulching increased by 76.03, 45.80, 39.17 and 24.78%, respectively. Specifically, there was a significant increase in soil available nitrogen (63.60%; p = 0.02) at < 50 mg kg−1 quantity with effect size of 1051.16 [CI: 194.86, 1907.45] and SOM (33.24%; p = 0.0007) at > 10 g kg−1. In terms of crop yield, results showed the moderating effect of soil texture on wheat yield. For example, there was no significant difference in wheat yield (p = 0.46) between the plastic film mulch application and the flat planting in heavy textured (clay loam, silt clay, and clay) soils in Inner Mongolia. The I2 test showed no heterogeneity between studies considered in the MA (Table 3). Plastic film mulching, however, increased potato and maize yield by 34.01 and 33.26%, respectively, compared to the flat planting.

Influence of straw mulched ridge-furrow on soil properties and maize yield in Shaanxi province

Straw mulching increased total nitrogen (90.11% at < 1 g kg−1), available phosphorus (78.48% at < 20 mg kg−1), SOC (62.04% at ≤ 10 g kg−1) and available potassium (29.23% at < 100 mg kg−1; 32.69% at > 100 mg kg−1). This could be attributed to longer sunshine hours per growing season. In areas with sunshine hours longer than 1300 h, straw mulched ridge and furrow rainwater harvesting system had an overall significant effect (p = 0.04) on maize as compared with the flat planting without mulching. Maize yields in Shaanxi province increased by 13.93% and ranged from 5247–10,264.85 kg ha−1 in straw mulched fields compared to the flat planting without mulching. The effect size was 2179.22 and the 95% confidence interval ranged from 373.60 to 3984.84. However, in terms of climatic variables like air temperature and precipitation, the MA demonstrated that in maize cultivation, air temperature and precipitation had no significant moderating effect (p > 0.05) on maize with straw applied as mulch compared with flat planting without mulching (Fig. 3).

Influence of co-application of plastic film and straw in ridge-furrow on soil properties and wheat and maize yield

Average maize yield in Shaanxi was 9412.22 kg ha−1 (p < 0.00001) and ranged from 7167.5–12,122.67 kg ha−1, with an effect size of 2599.44 compared with wheat yield which on average was 3862.17 kg ha−1 and ranged from 2972.33–4752 kg ha−1. The observed trend is probably because of the significant (20.48%; p < 0.00001) increase in soil available phosphorus at > 20 mg kg−1, with an effect size of 2423.80 [CI: 1578.54, 3269.07]. Conversely, air temperature at 10–20 °C with an effect size of 2423.80 significantly (p < 0.00001) increased wheat yield (by 60%) in areas with precipitation greater than 500 mm. The MA demonstrated that wheat and maize yield was significantly (p = 0.01) increased with co-application of plastic film and straw mulching in ridge-furrow compared with flat planting without mulching (Fig. 3).

Discussion

Effect of integrating mulching in ridge and furrow rainwater harvesting systems on soil properties

Inappropriate land use and management practices pose threats to soil sustainability because it can lead to soil organic matter (SOM) depletion, soil compaction, water and wind erosion, and decreased N use efficiency (Koch et al. 2015; Kassawmar et al. 2018). The impacts of climate change, particularly global warming and rainfall variability is projected to heighten management-induced threats on soil sustainability (Lal et al. 2011; El-Khoury et al. 2015). Therefore, improving soil nutrients is a necessity to increase crop production in modern agriculture (Wichelns 2016; Mak-Mensah et al. 2021c). The MA showed that the addition of crop residues as biochar and/or mulch to soil improves soil quality by releasing organic carbon, and essential macro and micronutrients to the soil for plant use. The results from the MA showing increased SOC in the biochar amended soil is consistent with the previous findings that soil amendment with biochar increases soil carbon (Liu et al. 2016; Blanco-Canqui 2017; Razzaghi et al. 2020). Biochar is regularly inhabited by actinomycetes bacteria, and arbuscular mycorrhizal fungi, so increased SOM following biochar application could be a reflection of microbial C responses (Verheijen et al. 2019; Cooper et al. 2020). Through surface catalytic activity, biochar adsorbs soil organic molecules and stimulates organic molecule polymerization to form SOM (Zhang et al. 2016; Gaimei et al. 2017).

Huo et al. (2017) reported that straw mulch with plastic film mulching increased SOC in dry saline soils compared with the control without mulch and plastic film (Huo et al. 2017). In this MA, co-application of plastic film and straw or biochar on ridges and in furrows increased available potassium, available phosphorus, SOM, total phosphorus, and total nitrogen (Fig. 4). The MA also showed that biochar amendment led to increase soil pH (Fig. 4). The ability of biochar to increase soil pH is generally attributed to (i) its alkalinity and release of base cations, particularly K+ and Ca2+, as well as the replenishment of soil Al3+ and H+ on negatively charged soils (Masud et al. 2014), (ii) the negatively charged functional groups (e.g., phenolic, carboxylic, and hydroxyl) present in biochar binds excess H+ ions in the soil solution (Gul et al. 2015), and (iii) increase organic anions decarboxylation as a result of increased attack of organic anions by microbes, which may consume surplus H+ from soil solution (Wang et al. 2014).

Fig. 4
figure 4

Odds ratios of crop yields in ridge-furrow rainwater harvesting systems with mulching. The error bars signify 95% confidence intervals, and the values above the bars indicate the number of observations (n)

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An increase in pH can improve soil quality by decreasing harmful elements like Al availability and improving plant nutrient availability (Bedassa 2020). Also due to its alkalinity, application of biochar to acidic soils increases the soil pH, which boosts readily available soil nutrients for to promote crop growth (Lourembam et al. 2018). Wang et al. (2012) revealed soil pH increased after maize straw was co-applied with urea in a paddy flooded silt loam soil. The authors attributed the increase in soil pH to the release of base cations. Further, given its high specific surface area and porosity, biochar improves soil nutrient retention and soil permeability for crop growth (Glaser et al. 2002; Blanco-Canqui 2017). High porosity of biochar decreases soil bulk density to promote root growth and increase soil water retention for plant uptake (Blanco-Canqui 2017).

Results of the MA indicating increased soil total nitrogen for the biochar amended soils are consistent with previous findings by Spokas et al. (2012) and Huang et al. (2013) who reported that biochar can preserve nitrogen due to its porosity and large surface area. Furthermore, biochar has been shown to improve nitrogen adsorption and retention, reduce soil nitrogen loss, improve nitrite to ammonia oxidation, and increase soil nitrogen availability by increasing NO3-N quantity (Nelissen et al. 2013; Case et al. 2015).

Biochar typically has high potassium (K), content which increases soil K status by enriching K-containing salts (e.g., KHCO3) (Karim et al. 2017). According to Karimi et al. (2020), corn residue biochar produced at higher temperatures (200–600 °C) increased calcareous soil K status by 1.52 to 2.59 folds. Khadem et al. (2021) found a 12.41 percent increase in available K after corn biochar amendment in two calcareous soils. Naeem et al. (2017) found that K increased (32–415 mg kg−1) in calcareous soil after wheat residue biochar produced at 300–500 °C amendment. It important to point out that the effect of biochar on soil K is moderated by other soil properties such as clay mineralogy and innate K contributing capability (Li et al. 2009).

Increase in phosphorus in the biochar amended soil could be explained as biochar liming effect on acid soil which precipitates Al and Fe as Fe(OH)3 and Al(OH)3 thereby increasing phosphorus availability (Bedassa 2020). The pH range of 6.0 to 7.0 is where the most phosphorus is available (Bedassa 2020). For mineral soils, however, phosphorus is readily available at pH 6.5 (Bedassa 2020). Another reason for increase phosphorus in the biochar amended soil is the presence of available phosphorus in biochar. In other words, biochar contains high soluble phosphorus salt content resulting from pyrolyzing organic materials (DeLuca et al., 2012).

Effect of integrating mulching in ridge and furrow rainwater harvesting systems on crop yield

Mulching practice in rain-fed agriculture is gaining prominence in recent years due to its beneficial effect on soil quality and crop productivity (Mondal et al. 2020). This is particularly so in semi-arid areas where annual precipitation is rarely more than 250–600 mm (Cao et al. 2021; Mak-Mensah et al. 2022). In semi-arid areas, prolonged drought and erratic rainfall are major constraints to rain-fed agriculture contributing to crop failures. Thus, saving water in crop fields is an integral part of sustainable agricultural intensification approaches (Yuge and Anan 2011). In the present MA, the application of bare ridge-furrow rainwater harvesting technique increased maize yield by 33.10% compared to flat planting. According to Zhang et al. (2011), ridge-furrow rainwater harvesting technique increased rainwater collection and infiltration which can lead to improved crop yield. The effect of ridge-furrow rainwater harvesting on soil moisture and crop yield is moderated by factors such as soil bulk density and field capacity (Daryanto et al. 2016). According to Wang et al. (2020), ridge-furrow rainwater harvesting is most beneficial in regions with low field capacity and low soil bulk density.

In the semi-arid region of Eastern Kenya, Miriti et al. (2012) reported that yield of maize cultivated in tied-ridging rainwater harvesting system was higher compared with the flat planting. Tied-ridging rainwater harvesting system with minimal irrigation increased sorghum and maize yield in semi-arid China and central Tanzania (Dong et al. 2017; Habtemariam et al. 2019). Jensen et al. (2003) found that maize yield increased by 42% in tied-ridging with normal rainfall amounts, without any nutrient inputs. Conservation treatments such as mulching and tied-ridging increased maize yield by 65% under rainfall conditions of 549 mm (Enfors et al. 2011). Mak-Mensah et al. (2021a) found that combining biodegradable film mulch with biochar increased maize yield by 23% when compared to farmers' bare flat planting practices. Results of the MA showing increased crop yield in the mulch or biochar and tied-ridging compared to the flat planting is could be attributed to improved soil properties and soil moisture conservation leading to good soil quality for plant development and growth.

Tied ridging can be used to conserve rainwater for crops in regions where seasonal rainfall is insufficient to meet crop water needs. Tied-ridges keep water between the ties in the furrows through runoff reduction and increasing infiltration, which is especially important when rainfall is insufficient to support crop growth. However, Ndlangamandla et al. (2016) found no significant difference in sorghum yield between the mulching in tied-ridge-furrow system and the flat planting methods. The lack of significant difference could probably be due to high soil temperatures under the ridges, which may be undesirable for seed germination, and infiltration compared with flat planting (Mak-Mensah et al. 2021b). In this MA, plastic film mulch application increased potato and maize yields in Gansu, Shaanxi, Ningxia, and Shanxi all located in semi-arid areas compared to flat planting (Fig. 4). This might be due to the ability of plastic film to keep topsoil moisture stable and minimize evaporation (Zhou et al. 2009). The increased yield could also be due to the ability of plastic film to move groundwater to the topsoil via vapor transfer and capillary action (Tian et al. 2003). The stomata of plants grown in plastic film mulched fields were reported to be more opened than that in flat planting fields, which may have increased available soil water, accelerated plant development, increased shoot biomass and leaf area index in the former than the latter (Qin et al. 2014). Liu et al. (2014) reported that double mulching in ridge-furrow rainwater harvesting system with plastic film preserved soil moisture throughout the growing season and increased maize yield compared with flat planting. Results from this MA highlight the potentials of integrated ridge-furrow systems to improve soil quality and increase crop production in semi-arid regions.

Conclusions and perspectives

The complexity of factors limiting agricultural productivity, including poor soil quality and water stress suggest that a single soil and water conservation intervention may not be sufficient to effectively address crop productivity challenges in semi-arid regions. Integrated mulched ridge-furrow rainwater harvesting systems (RFRHs) could improve crop growth and yields. The MA demonstrated even though that biochar amendment increased organic carbon, soil pH, available potassium and phosphorus, the integration of biochar with RFRHs did not significantly change maize yield compared to the flat planting. RFRHs with plastic film mulching increased potato and maize yields in Gansu, Shaanxi, Shanxi, and Ningxia provinces all located in semi-arid areas compared to the flat planting. We conclude that the integration of RFRHs with soil amendments could thus, be an optimal agronomic practice for smallholder farmers to maximize yield under rain-fed conditions. The findings of this MA provide useful information on optimizing RFRHs and soil amendments to improve soil quality and crop production especially in semi-arid areas.