lnfluence of preceding crop and tillage system on forage yield and quality of selected summer grass and legume forage crops under arid conditions

Hend H.M.HASSAN ,El-Sayed E.A.EL-SOBKY ,Elsayed MANSOUR ,Ahmed S.M.El-KHOLY ,Mohamed F.AWAD ,Hayat ULLAH ,Avishek DATTA

1 Forage Crops Research Department,Field Crops Research Institute,Agricultural Research Center,Giza 12619,Egypt

2 Agronomy Department,Faculty of Agriculture,Zagazig University,Zagazig 44519,Egypt

3 Department of Biology,College of Science,Taif University,Taif 21944,Saudi Arabia

4 Agricultural Systems and Engineering,Department of Food,Agriculture and Bioresources,School of Environment,Resources and Development,Asian Institute of Technology,Klong Luang,Pathum Thani 12120,Thailand

Abstract Among the crop production factors,preceding crop and tillage management affect the sustainable use of soil resources and ultimately crop growth and productivity. This study aimed at investigating the impact of preceding winter crops (grass or legume) and different tillage systems on forage yield,quality and nutritive values of three summer grass (Sudan grass,pearl millet and teosinte) and two legume forage crops (cowpea and guar) under arid conditions. The results exhibited that growing forage crops after legumes (as berseem clover) produced the highest fresh and dry forage yields and quality attributes compared with grasses (as wheat) with the exception of crude fiber content,which was decreased. Moreover,tillage practices showed positive impact on forage yields and quality attributes. The maximum forage yields and quality parameters were recorded under conventional tillage (CT)practice compared with reduced tillage (RT) and no-tillage (NT) systems. Among the evaluated crops,the highest yields of fresh forage,dry forage,crude fiber,crude protein and total digestible nutrient were exhibited by grass forage crops (Sudan grass,pearl millet and teosinte),whereas the highest crude protein content and the digestible energy values were produced by legume forage crops (cowpea and guar). The maximum fresh forage,dry forage,crude fiber,crude protein,total digestible nutrient and digestible crude protein yields were produced by pearl millet followed by Sudan grass under CT and RT after berseem clover. The highest net return was recorded by sowing pearl millet after berseem clover and applying CT followed by RT practices,which could be recommended for the commercial production. Moreover,it could be assumed that the combination of growing grass forage crops after legume crops under CT or RT systems could enhance forage crop yield and quality with an improvement in soil properties for sustainable agriculture with low cost and the highest net income.

Keywords: soil tillage,preceding crop,forage quality,nutritive values,net return

1.lntroduction

Arid regions suffer from forage material scarcity and the problem increases during the summer season due to the competition between production of human food and animal feed. Current efforts are mainly focused on improving the yield and quality of forage crops to address this problem. Cropping sequence by rotating grasses with legumes in crop rotations leads to an improvement in soil properties and preservation of available natural resources to be utilized more efficiently (Negashet al.2018). Legumes in cropping sequence improve chemical and biological soil properties as well as enrich soil fertility and recuperation,which help increase yield potential of subsequent crops and reduce requirements of synthetic fertilizers into crop production system (Bagayakoet al.2000;Yusufet al.2009;Videnovi?et al.2013;Mansouret al.2021). Besides,integration of grass and legume crops in agricultural rotations enhances environmental and economic sustainability (Zentneret al.2002).

The tillage system in crop production aims to produce favorable conditions for seed germination and seedling establishment (López-Garridoet al.2014). The impact of tillage practices on soil properties is dependent on the intensity of tillage system,soil characteristics and environmental conditions (Ishaqet al.2002). In arid Mediterranean regions,farmers prefer practicing conventional tillage (CT) with soil inversion to prevent potential problems of soil compaction. Conventional tillage has several advantages related to soil quality,such as decreasing gas efflux,increasing soil organic carbon content and reducing soil erosion (álvaro-Fuenteset al.2007;Jemaiet al.2012;Alamet al.2014). On the other hand,there is a growing trend worldwide in adopting a reduced tillage (RT) system,with no use of moldboard plowing and retaining preceding crop residues on the soil surface (Lal and Pimentel 2007;Lahmar 2010;Lópezet al.2012). Additionally,no-tillage (NT) system is used and it has been claimed to improve certain chemical soil properties,but it worsens physical soil characteristics after a few years and exerts negative impacts on plant growth and productivity (López-Garridoet al.2014;Litkeet al.2017;Ordo?ez-Moraleset al.2019;Panasiewiczet al.2020).

There are considerable variations in forage productivity and quality among and within the grasses and legumes forage crops. In general,C4grasses,such as pearl millet(PennisetumglaucumL.) and Sudan grass (Sorghum sudanense(Piper) Stapf.),are consistently able to produce higher dry matter compared with C3crops,such as forage legumes,particularly in warm regions that are characterized by temperature above 30°C (Sinclair and Muchow 1999;Hay and Porter 2006). Legume crops are distinguished from grass ones through their ability to form symbiotic relationship with rhizobia bacteria and fix nitrogen (N2) from the atmosphere. Moreover,legumes are a very good source of dietary protein for animals compared with grasses. Nutritionally,legumes have higher levels of energy per unit weight than grasses(Dewhurstet al.2009). On the other hand,grass forage crops are important in feeding ruminant livestock for their high dry matter production and low cost of cultivation(Capstaff and Miller 2018). Furthermore,grass forage crops produce higher fresh and dry forage yields compared with legumes (Amanullahet al.2016).

The influence of winter grass or legume crops managed under different tillage systems on the performance of grass and legume summer forage crops has not been thoroughly investigated under arid environments in Mediterranean regions. We hypothesized that growing grass forage crops after legume crops under CT or RT system would enhance forage crop yield and quality with an improvement in soil properties. Therefore,the present study aimed at investigating the impact of preceding winter crops (grass or legume) and tillage systems (NT,RT and CT) on three summer grasses and two legume forage crops to find out the possibility of increasing forage crop yields and quality with improving soil properties for sustainable agriculture.

2.Materials and methods

2.1.Experimental site

Field experiments were conducted during two growing summer seasons of 2019 and 2020 at the experimental farm of Kafr Al-Hamam Agricultural Research Station,Agricultural Research Center,Al Sharqia Governorate,Egypt (30°36′49′′N,31°30′56′′E). Soil samples were collected from the sites of preceding crops (wheat (Triticum aestivumL.) and berseem clover (TrifoliumalexandrinumL.)) at a depth of 0-60 cm before sowing summer crops in both seasons to determine soil physical and chemical properties (Table 1). Three soil cores were collected from random positions across the field. Moreover,meteorological data during the growing period and longterm average of 35 years are presented in Table 2.

Table 1 Chemical properties of the experimental soil after two winter preceding crops during the two growing seasons of 2019 and 2020

Table 2 Monthly average minimum temperature (Min.),maximum temperature (Max.),relative humidity (RH) and total precipitation(Prec) in 2019 and 2020 growing seasons as well as 35-yr monthly average (1985-2020)

2.2.Experimental design and agricultural practices

The experimental design was a strip-split plot design with three replications in which the vertical-plots were allocated to preceding crops,while the horizontal-plots were assigned to tillage treatments and the sub-plots were randomly assigned to forage crops (Fig.1). Each sub-plot consisted of six rows (5 m long) with 0.6 and 0.2 m spacing between rows and hills,respectively. The vertical-plots were separated by an alley of 3 m,horizontal-plots by 2 m and split-plots by 1 m alley. The used winter preceding crops were wheat in the first vertical strip and berseem clover was in the second one. The applied tillage systems were NT,RT and CT;NT was allocated to the first horizontal strip,RT to the second one and CT to the third one. No-tillage was applied by directly sowing into the stubble of preceding crop without any soil preparation (absence of tillage),RT was applied using a chisel plow by ploughing the soil once to 30 cm depth after harvesting preceding crop followed by leveling and CT was applied by ploughing the soil twice in two different directions to 30 cm depth using a chisel plow followed by disc harrowing and leveling. The forage crops were allocated inside the subplots (Fig.1). The used forage crops were three grass crops that included Sudan grass (Sorghumsudanense(Piper) Stapf.cv.Giza-2),pearl millet (PennisetumglaucumL.cv.Shandawil)and teosinte (EuchlaenamexicanaSchrad.cv.Baladi) and the legume forage crops were cowpea (VignaunguiculataL.cv.Baladi-1) and guar (CyamopsistetragonolobaL.cv.Baladi). The sowing dates for all forage crops were in mid-May in the two growing seasons. The seeding rate was set as recommended for commercial production at 35 kg ha-1for Sudan grass,pearl millet and cowpea,while at 45 kg ha-1for teosinte and guar. Before sowing,70 kg P2O5ha-1as calcium superphosphate (15.5% P2O5) and100 kg K2O ha-1as potassium sulfate (48% K2O) were added. Nitrogen fertilizer was applied at a rate of 250 kg N ha-1in the form of urea (46% N) in three equal doses:with first irrigation after sowing and after 1st and 2nd cuts,respectively,for grass forage crops. Nitrogen fertilizer was added at 40 kg N ha-1as ammonium sulfate (21% N) once at sowing for legume forage crops. All recommended agronomic practices for commercial production of forage crops including irrigation and pest management were applied.

2.3.Measured traits

Three cuts were taken in both seasons: The 1st cut was at 60 days after sowing,while the 2nd and 3rd cuts were taken after 40-day intervals for all forage crops under the study.At each cut,10 plants were collected from each sub-plot to determine plant height (cm). All plants were hand clipped and weighed for each plot,which were then converted to t ha-1to estimate fresh forage yield. Representative 500-g samples were taken and dried at 105°C until constant weight to estimate dry matter percentage (DM%). The dry forage yield (t ha-1) was calculated by multiplying fresh forage yield (t ha-1) by DM%.

2.4.Forage quality and nutritive values

The chemical analysis was performed following the recommended method by AOAC (1999). Samples were taken from each cut,dried at 70°C and grinded to fine powder to determine crude protein content (CPC) and crude fiber content (CFC). Crude protein content was recorded by multiplying N percentage by 5.88 for grasses and 6.25 for legumes (AOAC 1999). Crude protein yield (CPY,kg ha-1) was estimated by multiplying forage dry yield by CPC (%). Crude fiber yield (CFY,kg ha-1)was estimated by multiplying forage dry yield by CFC(%). Total digestible nutrients (TDN) were estimated as described by Church (1991): TDN for grasses(%)=[(50.41+1.04CPC)-(0.07CFC)] and TDN for legumes(%)=[(74.34+0.35CPC)-(0.73CFC)]. The digestible crude protein (DCP) was determined as DCP (%)=(0.9115CPC-3.62) according to McDonaldet al.(1995). Also,the digestible energy (DE) value of forage was calculated according to Heaney and Pigden (1963): DE (kcal g-1of dry matter)=0.546+0.055(TDN %). The CPC (%),CFC(%),TDN (%) and DCP (%) were multiplied by the dry forage yield (t ha-1) to calculate CPC,CFC,TDN and DCP yields (kg ha-1).

2.5.Economic analysis

Total costs of applied agricultural practices including seeds,fertilizers,irrigation,power,labor,machinery and land rent were calculated. The costs of all farm operations were calculated based on the official and the actual market prices determined by the Egyptian Ministry of Agriculture (Economic Reports 2020). Three economic parameters were estimated: total income (US$ha-1),net return (US$ ha-1) and return on investment(US$). The total income from forage yield was calculated by multiplying total fresh forage yield by actual price,which was US$ 76.8 t-1for Sudan grass,pearl millet and teosinte,while US$ 61.5 t-1for cowpea and guar. Net return from the production of forage crops was estimated as the difference between total income and total cost.Besides,return on investment was calculated by dividing total income by total cost.

2.6.Statistical analysis

The data were statistically analyzed using R Statistical Software version 3.6.1 (R Core Team 2020). Combined ANOVA was performed across the two growing seasons after testing the homogeneity of the experimental errors by Bartlett’s test. Strip-split plot analysis was applied where the vertical-factor (A) was preceding crops,the horizontal-factor (B) was tillage treatments and the subfactor (C) was forage crops based on the following mathematical model:

Yhijk=m+Rh+Ai+eAhi+Bj+eBhj+ABij+eABhij+Ck+ACik+BCjk+ABCijk+et

whereYis the observation,mis the general mean,Rhis the random block effect,Aiis the horizontal strip effect,Bjis the vertical strip effect andCkis the effect of the subplot,whileeAhi,eBhj,eABhij,andetare the error terms. Differences among treatments were separated by the least significant difference test atP≤0.05. Principal component analysis was performed on the averages of the evaluated traits to study their interrelationships.

3.Results

3.1.Forage yield

Preceding crop and tillage system displayed significant impacts on plant height,fresh and dry forage yields averaged across seasons (Table 3).Planting berseem clover as a preceding crop significantly increased those traits compared with wheat as the preceding crop. This resulted in an average increase in plant height of 4.6% and total fresh forage and total dry forage yields of 19%.Tillage treatments significantly impacted the aforementioned traits showing a gradual increase as tillage intensified(Table 3). Regarding the forage crops,Sudan grass and pearl millet were the tallest and produced higher yields than others.

Moreover,the results revealed that the aforementioned traits were significantly higher in all forage crops after berseem clover as a preceding crop compared with wheat. In this context,the relative increase in the three cuts in average was 4.6% plant height,21.9% total fresh forage yield and 16.2% total dry forage yield due to sowing forage crops after berseem clover than wheat. Likewise,tillage practices exhibited highly significant impacts on plant height and forage yields in all cuts. Conventional tillage practice had positive effect on plant height and forage yields;the highest plant height (114.1 cm as an average of three cuts),total fresh forage yield (85.1 t ha-1)and total dry forage yield (16.4 t ha-1)were assigned for CT compared with RT and NT. Moreover,the evaluated grass and legume forage crops exhibited highlysignificant differences in plant height,fresh and dry forage yields (Table 3). Sudan grass had the highest plant height followed by pearl millet and teosinte in all cuts,and the shortest plant height was recorded for legumes crops.Similarly,pearl millet had the highest fresh and dry forage yields followed by Sudan grass in all cuts,and the lowest forage yield values were assigned to legume forage crops. Obviously,the first cut exhibited the highest fresh forage yield in evaluated forage crops,except for teosinte with the highest yield in the second cut. Likewise,the first cut displayed the highest dry forage yield for legumes crops,while it was the second cut for grasses. On the other hand,the third cut displayed the highest plant height for all evaluated crops.

Table 3 Influence of preceding crop and tillage system on plant height,fresh and dry forage yields of five forage crops

The interactions between studied factors were significant for plant height and forage yields. The threeway interaction revealed that Sudan grass exhibited the tallest plants (170 and 166 cm) followed by pearl millet(146 and 139 cm) under CT and RT,respectively,after berseem clover (Fig.2-A). Otherwise,the shortest plants were evident for cowpea (48.9 cm) and guar (52.6 cm)under NT after wheat. The highest total fresh forage yield was produced by pearl millet (129.5 and 128.7 t ha-1) followed by Sudan grass (120 and 114 t ha-1) under CT and RT,respectively,after berseem clover (Fig.2-B).Otherwise,the lowest total fresh forage yield (34.8 t ha-1)was recorded by cowpea under NT after wheat. Likewise,higher total dry forage yield (26.5 and 24.7 t ha-1) was evident with pearl millet followed by Sudan grass (24.7 and 22.5 t ha-1) under CT and RT,respectively,after berseem clover (Fig.2-C).

3.2.Forage quality

Quality parameters and nutritive values of forage crops including CPC and CFC,CPY,CFY,TDN,DCP and DE were significantly impacted by preceding crops,tillage systems,forage crops and their interactions (Tables 4-6).The uppermost CPC,CPY and CFY were obtained after berseem clover in all cuts. Otherwise,the highest CFC was recorded after wheat in the three cuts. Likewise,preceding crops had significant effects on TDN and DCP yields as well as DE in the three cuts (Table 6).Obviously,sowing forage crops after berseem clover produced the highest values for both TDN and DCP yields as well as DE compared with wheat in all cuts. Moreover,tillage systems displayed significant impacts on CPC,CFC,CPY,CFY,TDN,DCP and DE in all cuts (Tables 4-6). Conventional tillage exhibited the highest values for all abovementioned parameters,except CFC,followed by RT and NT in all cuts (Tables 4-6). With respect to forage crops,cowpea possessed the highest CPC followed by guar and teosinte (Table 4). The maximum CFC values were produced by Sudan grass followed by pearl millet and guar. Additionally,the highest CPY and CFY were evident with pearl millet followed by Sudan grass (Table 5).Moreover,pearl millet resulted in the highest TDN and DCP yields. Nevertheless,the highest DE values were produced by legume crops and the lowest values were recorded by grass crops (Table 6). The first cut exhibited the highest CPC and CPY in evaluated forage crops.Similarly,the first cut displayed the highest CFC for grass crops,while it was the third cut for legumes.

Table 4 Influence of preceding crop and tillage system on crude protein content and crude fiber content of five forage crops

Table 5 Influence of preceding crop and tillage system on crude protein yield and crude fiber yield of five forage crops

The interaction results revealed significant effects on all quality parameters (Figs.3 and 4). The highest CPC was produced by cowpea followed by guar under the three tillage systems after berseem clover as the preceding crop (Fig.3-A). Otherwise,the lowest CPC was assigned to Sudan grass under the three tillage systems after both preceding crops (wheat and berseem clover). The lowest CFC was evident with cowpea under the three tillage systems after berseem clover (Fig.3-B). The highest CFC was recorded by Sudan grass under all tillage systems after wheat. The highest attainable total crude protein yield was recorded by pearl millet under CT after berseem clover,while the lowest values were assigned to guar and cowpea under NT after wheat (Fig.3-C). In addition,the highest total CFY was obtained by Sudan grass and pearl millet under CT after berseem clover,while the lowest values were recorded by cowpea and guar under NT afterwheat (Fig.3-D). Moreover,pearl millet exhibited the highest TDN yield under CT after berseem clover,while the lowest values were recorded by cowpea and guar under NT after wheat (Fig.4-A). In addition,the highest DCP yield was obtained by pearl millet,cowpea and guar under CT after berseem clover,while the lowest values were recorded by Sudan grass and guar under NT after wheat (Fig.4-B). The highest DE values were obtained by cowpea under the three tillage systems after berseem clover,while the lowest values were recorded by Sudan grass under the three tillage systems after berseem clover and wheat (Fig.4-C).

3.3.lnterrelationship among traits

Principal component (PC) analysis was applied to visualize the association among the evaluated yield traits and quality parameters in grass or legume forage crops. The first two PCs showed most of the variance,which was about 80.75 and 86.83% for grass and legume forage crops,respectively,in the same order. Therefore,the two first PCs were used to construct PC-biplot (Fig.5).The trait vectors,represented by acute angles,indicate positive associations,while vectors with angle more than 90° suggest negative association. Accordingly,the traits could be classified into two groups. In grass forage crops,the first group consisted of CPC and DE,while the second group contained remaining traits. Likewise,in legume crops,the first group included CFC,while the second group comprised of remaining traits.

3.4.Economic analysis

Economic performance of the interaction among tillage systems,preceding crops and diverse forage crops was assessed (Table 7). The highest total income was obtained by sowing pearl millet after berseem clover using CT followed by pearl millet after berseem clover using RT.Likewise,the highest net return was achieved by sowing pearl millet after berseem clover using CT followed by pearl millet after berseem clover using RT. On the other hand,the lowest net return was recorded by sowing cowpea after wheat using NT followed by guar after wheat using NT.

4.Discussion

The obtained results demonstrated that the combination of growing grass forage crops after legume crops under CT or RT system could increase forage crop yield and quality in arid environments with an improvement in soil properties for sustainable agriculture with low cost and the highest net income,which has supported our hypothesis as raised in the Introduction section. This could contribute to an increase in the production of forage crops under agricultural intensification to meet livestock demands,especially during the summer period that is characterized by forage scarcity (Kumaret al.2005).

Overall,the present study aimed at devising a cropping system for sustainable agriculture in arid regions by comparing the effects of preceding crops and tillage management systems on diverse forage crops. The study focused on the response of different grass and legume summer crops to preceding crops wheat and berseem clover,which occupy most of the cultivated area in the Mediterranean region during the winter season (Salama 2020). Intensive land uses with continuous growing of similar crops adversely impact soil health,crop productivity and exert a long-term negative effect on the environment. The obtained results indicated significant differences among grass and legumes forage crops under different preceding crops and tillage systems. Growing forage crops after legume crop (berseem clover) resulted in an increase in biometric,fresh and dry forage yields and quality parameters(CPC,CPY,CFY,TDN,DCP,and DE).These responses could be resulted from enhanced soil fertility with high organic matter and N content after berseem clover compared with wheat (Table 1). Legume crops lead to an improvement in chemical,physical and biological properties of soil by increasing biological N2fixation and organic matter (Veenstraet al.2007;Fageria 2009;Ayubet al.2011;Videnovi?et al.2013). Moreover,the taproots of legume crops are characterized by a high cation exchange capacity,which improves soil porosity and structure compared with grasses (Hay and Porter 2006;Fageria 2009). Besides,legume crops reduced soil pH (Table 1),which enhances plantsoil-microbial activity,nutrients availability and provides optimum conditions for crop growth and development (Fageria 2009;Gogoiet al.2018). In this context,Crottyet al.(2016) and Mansouret al.(2021)elucidated that legume as a preceding crop enhanced recycling plant nutrients and microbial activity as well as avoided an accumulation of toxin,which increasedcrop yield potential of the subsequent crops and final net income.

Table 6 Influence of preceding crop and tillage system on total digestible nutrient yield,digestible crude protein yield and digestible energy of five forage crops

Table 7 Estimates analysis of costs for inputs farm operation and profitability of five forage crops as affected by preceding crop and tillage system

With respect to tillage systems,the results revealed that CT caused a significant improvement in plant height,fresh forage yield and dry forage yield of five forage crops compared with RT and NT. Besides,CT caused significant increase in quality parameters and nutritive values,such as CPC,CPY,CFY,TDN,DCP,and DE.These findings could be attributed to improved soil properties due to incorporated residues of preceding crops before sowing and thereby increasing organic matter and nutrients contents. Conventional tillage has been reported to improve soil quality,soil organic carbon and biodiversity,which in turn help increase the available nutrients for subsequent crops (álvaro-Fuenteset al.2007;Madejónet al.2007;Jemaiet al.2012;Lópezet al.2012). In this context,Kumaret al.(2018) manifested that forage yield and quality depend mainly on its genetic background,but it could be improved by employing adequate agronomic interventions including tillage system,nutrient management and harvesting stage. Furthermore,Singeret al.(2004),Rusuet al.(2006) and De Vitaet al.(2007) deduced that minimized soil tillage systems had no negative effects on yields of grasses or legumes crops.Moreover,Sainjuet al.(2007) reported that long-term RT increased soil carbon storage and soil quality by boosting microbial biomass and their activities than conventional agriculture. Riegeret al.(2008) and Litkeet al.(2017)demonstrated reduction in grass yield under NT system.Otherwise,Ordo?ez-Moraleset al.(2019) showed that yield of grass crops decreased under NT compared with CT. In addition,Panasiewiczet al.(2020) reported that the productivity of crop rotation was lower under RT and NT systems compared with CT. In contrast,Rezaet al.(2015) mentioned that tillage systems,such as NT,RT and CT,did not show significant effects on pearl millet and cowpea productivity.

The evaluated forage crops responded differently in terms of forage yield and quality parameters. The grass forage crops produced higher fresh and dry forage yields. These differences could be due to the variation in genetic background in used crops and their interaction with environmental conditions. Furthermore,increased temperature above 30°C during the two growing seasons(Table 2) might lead to an increase in net photosynthetic rate of C4grasses,such as Sudan grass,pearl millet and teosinte,and thereby increased dry matter production compared with C3crops. In this aspect,Hay and Porter(2006) reported that C4crops have typically more photosynthetic efficiency than C3crops in serving CO2and building up dry matter due to lower light compensation.Moreover,an absence of photorespiration in C4plants cannot be negated in this condition. Photorespiration is considered as a wasteful and energy-consuming process during photosynthesis in C3plants,which ultimately leads to a reduction in dry matter production (Sinclair and Muchow 1999). Moreover,Amanullahet al.(2016),Solatiet al.(2017) and Capstaff and Miller (2018) manifested that grass forage crops produced higher fresh and dry forage yields compared with legume ones.

Sudan grass and pearl millet produced the highest CPY,CFY,TDN and DCP yields. Otherwise,the highest DE values were produced by legume crops,while the lowest values for DE were recorded by grass ones.Moreover,DE displayed positive association with fresh forage yield and dry forage yield in legume crops,while negative association in grass crops (Fig.5). In this matter,Dewhurstet al.(2009) showed that legume crops tend to have higher levels of energy per unit weight than grass crops. Similarly,legumes forage crops (cowpea and guar) possessed superiority in CPC,while lower CFC compared with grass crops (Sudan grass,pearl millet and teosinte). In that connection,CPC displayed negative association with CFC in both grass and legumes crops (Fig.5). It appears that increasing CPC might have decreased CFC. Moreover,CPC was negatively associated with fresh forage yield and dry forage yield in grass crops,while it was positively associated with legume crops (Fig.5). This might be due to the dilution effect that resulted from higher dry matter production of grasses than legume forage crops (Jainet al.2010;Abuneran 2013). On the other hand,increasing CPC in legume crops did not compensate the reduction in dry matter production compared with grasses. In contrast,grasses produced higher dry matter,which compensated the reduction in their protein contents. Dry matter production is an important factor in determining CPY per unit area (Abuneran 2013). These results suggest a possibility of producing a high forage yield with a high CPY,which is desired from an economic standpoint,and it also enhances the palatability and digestibility (de Araüjoet al.2002;Türket al.2015).

With respect to the three-way interaction,the highest fresh and dry forage yields,CPY,CFY,TDN and DCP were produced by pearl millet and Sudan grass under CT and RT after berseem clover. The lowest fresh and dry yields were recorded by cowpea and guar under NT after wheat. This effect could be attributed to direct or indirect positive roles of preceding legume crop and tillage practices on soil physico-chemical properties by enriching N availability,organic carbon,nutrients and organic acids and by improving soil properties (Crottyet al.2016;Mansouret al.2021;Ordo?ez-Moraleset al.2019;Panasiewiczet al.2020). These positive impacts are reflected in enhancing forage yield,especially grass forage crops,which are characterized by their ability and higher efficiency in dry matter production compared with legume ones (Amanullahet al.2016;Solatiet al.2017).Additionally,the highest detected net return was recorded by sowing pearl millet after berseem clover and using CT followed by RT,while the lowest net return was recorded by sowing cowpea after wheat with NT practice.

5.Conclusion

The results of this study highlighted the importance of certain agronomic practices that secure increasing summer forage quantity and quality. The results revealed that sowing fodder crops after legume crops (as berseem clover) produced the highest fresh and dry forage yields,as well as quality attributes and nutritive values compared with grass crops (as wheat). Tillage management also had a substantial effect on yield and quality of forage crops. The highest forage crop yields and quality attributes were recorded under CT practice. The highest forage yields and quality traits were produced by grass forage crops (Sudan grass,pearl millet and teosinte).Otherwise,the highest CPC and DE values were recorded by legume crops. Moreover,the highest net return was recorded by sowing pearl millet after berseem clover and using CT followed by RT,while the lowest net return was recorded by sowing cowpea after wheat with NT practice.The overall results referred to a complementary positive role between preceding legume crop,conventional or reduced tillage system with grass forage crop in maximizing forage yields and quality attributes with improving soil properties for sustainable agriculture.

Acknowledgements

The authors wish to thank the Agricultural Research Center,Giza,Egypt,and the Taif University Researchers Supporting Project (TURSP-2020/111),Taif University,Taif,Saudi Arabia for the technical and financial support to this research.

Declaration of competing interest

The authors declare that they have no conflict of interest.