Abstract
Understanding processes that ameliorate structural degradation in sandy soils is particularly important in intensively managed potato (Solanum tuberosum L.) systems. Seven 2‐yr potato rotation systems were evaluated over 3 yr in an irrigated field trial comparing winter management systems bare (B) and cover crops: rye (Secale cereale L.; R), rye‐hairy vetch (Vicia villosa Roth; RV) mixture and red clover (Trifolium pratense L.; C). Crops rotated with potatoes (P) were snap bean (Phaseolus vulgaris (L.); SB), wheat (Triticum aestivum L.; W) and sweet corn (Zea mays L.; SC). The systems consisted of: S1 PBSBB; S2 PRSBR; S3 PRSCB; S4 PWWR; S5 PWWCC; S6 PRVSBRV; and S7 PRVSCRV, both entry points evaluated each year. Carbon inputs above‐ and belowground were measured and systems grouped as low (S1 and S4), medium (S2 and S6), and high (S5, S3 and S7): 1.2, 2.0, and 2.8 Mg C ha−1, respectively. Response variables included water stable aggregate (WSA) size fractions, macroaggregates (≥0.25 mm) and microaggregates (<0.25 mm), mean weight diameter (MWD), soil C, nitrogen mineralization potential (NMP), and potato tuber yield. Systems with SC contributed twofold higher biomass than rotations with W or SB, and the presence of RC contributed higher amounts of carbon (1.2 Mg ha−1) compared to R (0.7 Mg ha−1). Only the entry year influenced macroaggregates in 2001; both entry year and cropping system influenced aggregate size classes in 2004. Over 3 yr the macro‐WSAs declined by 13%, except for high carbon input systems. Residue C input was a moderate predictor of total soil C (31% of variability explained), whereas macro‐ and micro‐WSAs were predictors of soil C, accounting for 58 and 72% of observed variability, respectively. Low levels of aggregation were observed in this sandy soil and the modest amounts of C inputs from winter cover crops posed a challenge to detecting treatment effects, which was in part overcome by georeferencing, to improve precision of sampling over time.
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