In our studies this could not be shown, probably because the organic matter contents and release of N were comparably small and thus system related differences were not visible against the general “noise” of spatial and temporal heterogeneity. Determination of the impact of tillage on WSA did not result in a clear-cut trend suggesting that reduced tillage and residue retention would always increase aggregate stability, as has been proven elsewhere. However, ambiguous results in regard to the influence of tillage and residue retention on WSA were also found by for Western Kenyan cropping systems under integrated soil fertility management.
A higher share of larger aggregates under ZT points towards better soil structure, which in turn positively affects soil water infiltration and retention—witnessed by our results on these properties. Further, more large aggregates in C16 than in B4 was most likely a positive effect of the higher SOM content in C16, as SOM is the glue that holds aggregates together. However, our observations show that WSAs change with soil depth. To reveal the underlying mechanisms further research is required to fully understand the impact of tillage on WSA of the high-clay, montmorillonitic soils of northern Syria, which are typical for the Mediterranean region. It was somewhat surprising that soil water infiltration capacity varied significantly over time, which basically meant, at least for the soils at ICARDA headquarters, that the applied method did not give consistent results complying with what could be considered saturated hydraulic conductivity. Also, quantities were much higher— at least a factor 10—than Ks-values established for the same soil .
Nevertheless, the consistency of results provides evidence about the soil ameliorating impact of ZT and residue management. An increased water infiltration capacity allows water to infiltrate deeper into the soil and diminishes water runoff and thus soil erosion. This has been known for many years, and has been shown in many other comparable studies, such as in Germany , USA , Australia , Poland , Argentina , and Mexico . On the other hand, observed surface crusting and decreased water infiltration under NT. Yet, despite reduced infiltration, their NT treatments still conserved more soil moisture during the dry fallow period than the tilled plots. also could not find any improvement in infiltration rate under ZT in comparison to chisel ploughing in Argentina. We tried to answer the question whether in addition to higher water infiltration capacity by reduced tillage and residue management a surface residue layer would conserve soil moisture.
During the late cropping season, high surface residue levels did not contribute to moisture conservation in the top 15 cm of soil, contradicting what has been reported elsewhere. However, increased crop transpiration—manifesting itself in significantly higher yields compared to the off-site control—could have confounded the results. After harvest, under fallow conditions, residues could in general not prevent the loss of soil moisture from 0 – 15 cm depth within about four weeks although moisture levels were some few per cent higher during the first three weeks under the plots with the two highest residue levels. This means residue retentionimpacted moisture in the top soil for a limited time only. Under fallow conditions the effect was still notable five weeks after application of 30 mm of irrigation water when including 15 – 30 cm depth into the calculation, but only if very high amounts of residue were retained; much more than can be produced on-site under dry rainfed conditions.
A temporary reduction of soil water evaporation during the cropping season when residues are retained should improve the crop-soil water balance by shifting water losses from unproductive evaporation to productive crop transpiration. However, a recent modelling study revealed that the impact is limited, not exceeding on average 10 – 15 mm per season that is transpired instead of evaporated . Corresponding yield data revealed that minimum tillage and residue retention translates into higher yields for all major crops of the region in the majority of years. Our data show that obviously this is due to the effect of an increased soil quality and more favorable soil water relations. Adequate, balanced nutrient management including crop nutrition by chemical fertilizer application is, of course, an underlying necessity. Our results provide evidence that SOM increased in response to N-fertilizer application, but further research is required to consolidate this observation.The lack of success of dams and embankments as a result of the use of dispersive soil has been recognized byengineers and geologists in South Africa and internationally for many years.