## 4 Discussion  
The increased Ksat upon adding FYM to inorganic fertilizer might be related to the enhanced structural stability of soil, increased OM, and improved surface soil biological activity. Farmyard manure and a balanced chemical fertilizer seem to contribute to better aggregation, thereby increasing effective pore volume. Given the dependence of soil permeability on effective pore volume, one may suggest a direct impact in terms of improved pore volume upon applying FYM on the Ksat of soil [34]. According to the results, the RT system with combined FYM + 50% of the recommended dose chemical NPK fertilizer application could increase Ksat significantly, possibly because of decreased density. Hydraulic conductivity is significantly affected by soil pore volume, and our findings showed that the application of FYM and choosing a suitable tillage (RT) can affect flow and transport through the soil matrix by improving the pores. These factors are very important in semi-arid regions, and they can determine the effective rain ratio for plants. the application of RT without the application of organic fertilizers will lead to failure in the short term. Figure 2: Effect of nutrient management practices and tillage systems on sunflower (_Helianthus annuus_ L) achene yield (AY: columns) and on the mean emergence time of seedling (MET: dashed line) during the years 2015 and 2016. The error bars indicate standard deviation. C: conventional tillage, R: reduced tillage, F1: control, F2: FYM at 20 Mg:ha\({}^{-1}\), F3: FYM at 40 Mg:ha\({}^{-1}\), F4: 50% of the recommended dose of chemical NPK + FYM at 20 Mg:ha\({}^{-1}\), F5: full recommended dose NPK fertilizer. Our results showed that there was a significant negative correlation between BD and OM. Given that potential factors determining soil density are mostly mineral and chemical, the organic contents of FYM can affect these factors, mainly by influencing the charges on colloid surfaces [35]. Furthermore, differences in tillage systems could be responsible for more extensive soil structure degradation and structure changes in the CT system. Following the same approach explained for soil tillage, machine traffic tends to deteriorate soil porosity, thereby increasing BD. A difference observed between the years can be related to the accumulated effects of fertilizer and aridity of the first year. The significant correlation of FYM and tillage effects with BD showed that the soil organic matter and carbon levels are now below their critical level in the studied site, and this status was noticeable under the RT system. Our findings demonstrate that the combined effects of tillage and fertilizer should be considered in soil management; however, the effect of FYM was more prominent than other treatments. These results demonstrate that, in RT systems, it is necessary to apply significant amounts FYM or adopt proper crop residue management. The resultant increase in SOM can be attributed to the increased macro-aggregate stability of clay soils, possibly because of promoted microbial populations and the aggregation of clay- and silt-sized particles to form macro-aggregates using the microbe-produced mucilage [36; 37; 38]. Studies showed that the distribution of dominant populations of microorganisms is affected by tillage system, thereby highlighting differences among various tillage systems. However, generally, microbial activities follow slower trends in RT systems than in CT systems where OM is supplied to the soil. Likewise, incorporating farmyard manure into the soil and RT reportedly increased the OM content of the soil, protected the soil against erosion, and resulted in enhanced porosity and aggregation of the soil, which enhanced the water retention and infiltration characteristics of the soil while reducing its mechanical impedance. Soil moisture was considerably increased by FYM application under RT in the second year. The soil had very low SOM before the application of farmyard manure.