Assessment of Soil Compaction under Center Pivot Irrigation Systems and its Effect on Crop Performance

A field study on two 12.5 ha plots cultivated with wheat and alfalfa was conducted to determine Soil Compaction (SC), its spatial variability and its effect on crop performance under center pivot irrigation systems. Considering compaction at two tested soil depths, results revealed that the soil of the alfalfa plot exhibited significantly (p<0.01 and p<0.05 for 0 to 10 cm and 0 to 30 cm soil depth, respectively) higher compaction values (an average of 1730.328 and 2329.604 kPa, respectively) compared to those exhibited by the soil of the wheat plot (averaging at 1339.685 and 2088.903 kPa, respectively). Significant spatial variation of SC was observed within each of the tested plots. SC around pivot wheel tracks was also investigated at a soil depth of 0 to 30 cm for 5.5 m wide strips on both sides of the tracks. Results revealed that the Coefficient of Variation (CV) of the SC around the tracks was 9.33 and 16.53% for alfalfa and wheat plots, respectively, suggesting that the SC was not laterally influenced by the wheel tracks. The effect of SC on crop performance, expressed as the Normalized Difference Vegetation Index (NDVI), was investigated on the two plots. Results showed that the NDVI was, in general, inversely proportional to the SC. For both crops, the NDVI was more affected by SC at the top soil layer (0-10 cm depth). Moreover, the alfalfa crop was shown to be significantly influenced by the SC (an average R2 value of 0.3165 and P value of 0.0287), unlike the wheat crop (an average R2 value of 0.0725 and P value of 0.4646).