Recycling of organic wastes via their incorporation in cultivated lands is known to alter soil structural stability. Aggregate stability tests are commonly used to express quantitatively the susceptibility of soil structural stability to deformation. The objective of this study was to investigate the effects of biosolids addition, namely composted manure (MC) and activated sludge (AS), and spiking of the soils with orthophosphate (OP), phytic acid (PA) or humic acid (HA), on soil aggregate stability of semi-arid loamy sand, loam and clay soils before and after subjecting the soils to six rain storms (each 30 mm rain with a break of 3–4 days). Aggregate stability was determined from water-retention curves at high matric potential. The effects of the applied amendments on pre- and post-rain aggregate stability were inconsistent and soil-dependent. For the pre-rain state, all of the tested amendments improved aggregate stability relative to the control. For the post-rain condition, aggregate stability was lower in the MC, OP and PA treatments and higher in the AS and HA treatments than in the control. The coarse-textured loam and loamy sand soils were more affected by the soil amendments than the clay soil. For the pre-rain state, addition of organic matter significantly improved macro-porosity and hence the stability of apparent macro-aggregate (>250 μm). Our results indicate a possible advantage for separation of aggregates into macro- and micro-aggregates for more precise evaluation and understanding of the effects organic amendments might have on aggregate stability.

Application of organic wastes to cultivated lands can replace mineral fertilizers but may also alter soil physical properties and enhance pollution potential. The objective of this study was to investigate the effects of biosolids [composted manure (MC) and activated sludge (AS)] and specific biosolid component [orthophosphate (OP), phytic acid (PA) and humic acid (HA)] application on soils differing in texture [loamy-sand (Ramat-HaKovesh, RH), loam (Gilat, GL) and clay (Bet-Dagan, BD)], infiltration rate, runoff volume and soil sediment loss. The soils were packed in erosion boxes (400 × 200 × 40 mm) and subjected to six consecutive simulated rainstorms, each of 186 mm deionized water. The results showed that runoff volume and sediment loss from untreated soils increased with increasing clay contents. In treated soils, the response to AS application differed from the response to other amendments; in the BD clay and GL loam, it was the only amendment that caused a decrease in sediment removed by runoff. In the RH loamy-sand, all amendments reduced the final infiltration rate, but only AS and HA increased the measured runoff. It is proposed that the difference in the response of the soils to the amendments is associated with the soil's ability to attenuate changes in the negative charge on the clay edges following the increase in the specific adsorption of charged anions, thus controlling clay swelling and maintaining aggregate integrity. The effects of amending soils with a source of organic matter in order to control runoff and soil erosion are not straight forward and depend on soil and amendment properties

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Lettuce response to salinity has been studied in open irrigation systems but not under solution recycling conditions. The objective of this study was to determine effects of threshold EC values for solution replacement on stalk weight and quality, solution chemistry and quantities of water and nitrogen removed from the system. Results showed that lettuce yield response to threshold EC in recycled solutions was similar to response to steady salinity in open irrigation systems reported in the literature. The salinity induced yield decline was stronger in the spring than in the autumn growing season. Accumulated NaCl in solution reduced Mg, Ca and K concentration in leaves in the spring experiment, but only Mg was significantly correlated with untrimmed and trimmed stalk yield. Recirculation reduced water and nutrients discharge and hence their input into the system. Increasing the threshold EC from 2 to 4-5 dS/m reduced water discharges by 60-to-100%, while the yield decline was ~10% in autumn and ~20% in spring.

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