30% of the Rotational Effect Can be Explained By Soil Residual Water and Nutrients in Diversified Crop Rotations.

Soil residual water and nutrients availabilities are the two major properties of soil productivity. Diverse crop rotations with pulse crops may provide benefits by improving the use of soil water and nutrients and decreasing production inputs. A 4-yr crop rotation trial was conducted at Swift Current (50.28° N, 107.8° W), Saskatchewan, and Brooks (50.57° N, 111.89° W), Alberta, Canada. The objective of this study was to quantify the effect of pulse-based crop sequences in rotation and immediately-preceding crops on soil residual water and nutrients, and the agronomic performance of subsequent wheat in rotations. There were nine rotation systems (9 treatments) were evaluated, where pea (Pisum sativum L.), lentil (Lens culinaris Medik.), and chickpea (Cicer arietinum L.) were seeded in different intensities before wheat (Triticum aestivum L.). Averaged across three site-years, pea (P) and lentil (L) as the preceding crops before wheat (W) or the rotations with pea (PPPW and PWPW) and lentil (LLLW and LWLW) included more than once in the 4-yr sequences with wheat had the highest soil water and residual N in the 30-60 and 60-90 cm soil depths, while continuous wheat (WWWW) had the lowest. Preceding pea and lentil increased the grain yield of wheat by 26% and 18%, respectively, as compared with preceding wheat. Variance partitioning of the redundancy analysis revealed that soil residual water and residual N explained 24 to 36% of the yield variation observed for wheat, while the remainder of the rotational benefits were unaccounted for. Research on other aspects of the rotational effect such as soil microbial communities and disease and weed dynamics may provide further insight into the large rotational effect.