No abstract

Inclusion of cover crops (CCs) may be a potential strategy to boost no-till performance by improving soil physical properties. To assess this potential, we utilized a winter wheat (Triticum aestivum L.)-grain sorghum [Sorghum bicolor (L.) Moench] rotation, four N rates, and a hairy vetch (HV; Vicia villosa Roth) CC after wheat during the first rotation cycles, which was replaced in subsequent cycles with sunn hemp (SH; CrotaUria júncea L.) and late-maturing soybean [LMS; Glycine max (L.) Merr.] CCs in no-till on a silt loam. At the end of 15 yr, we studied the cumulative impacts of CCs on soil physical properties and assessed relationships between soil properties and soil organic C (SOC) concentration. Across N rates, SH reduced near-surface bulk density [\^^ by 4% and increased cumulative infiltration by three times relative to no-CC plots. Without N application, SH and LMS reduced Proctor maximum pj^, a parameter of soil compactibility, by 5%, indicating that soils under CCs may be less susceptible to compaction. Cover crops also increased mean weight diameter of aggregates (MWDA) by 80% in the 0-to 7.5-cm depth. The SOC concentration was 30% greater for SH and 20% greater for LMS than for no-CC plots in the 0-to 7.5-cm depth. The CC-induced increase in SOC concentration was negatively correlated with Proctor maximum pi and positively with MWDA and cumulative infiltration. Overall, addition of CCs to no-till systems improved soil physical properties, and the CC-induced change in SOC concentration was correlated with soil physical properties.Abbreviations: CC, cover crop; HV, hairy vetch; MWDA, mean weight diameter of aggregates; SH, sunn hemp; LMS, late-maturing soybean; SOC, soil organic carbon.

Under controlled irrigation, corn plants grown in large containers were subjected to water deficits in one of nine periods during each of two growing seasons. The first experiment (1965) differed from the second (1966) by somewhat different timing of treatments and by limiting soil fertility conditions. A significant grain yield reduction (12 to 15%) was observed after stress during the vegetative period at early ear shoot and ovule development in 1966. A 53% grain yield reduction was associated with stress at 75% silking in 1965. In the 3‐week period after silking, water deficits consistently reduced yields approximately 30% in both years. Significant reductions in kernel numbers were associated with yield reductions from stress before or during silking and pollination. Kernel weights were significantly reduced by stress during or after silking. Trends in the percentage of developed kernels in each of three ear sections indicated that the ability of kernels to compete for products of photosynthesis correlated with the comparative age of the ovule or kernel at the time of water deficit.

Impact of cover crops (CCs) on winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] yields is not well understood. We assessed crop yield and its relationships with CC-induced changes in soil properties for a 15-yr CC experiment in wheat-sorghum rotation at 0, 33, 66, and 100 kg ha -1 of N application in south central Kansas. Hairy vetch (Vicia villosa Roth) was used as a winter CC from 1995 to 2000, while sunn hemp (SH; Crotalaria juncea L.) and late-maturing soybean [LMS; Glycine max (L.) Merr.] were used as summer CCs in no-till from 2002 to 2008. Summer CCs increased crop yields particularly at low rates of N application. At 0 kg N ha -1 , SH increased sorghum yield by 1.18 to 1.54 times, while wheat yield increased by 1.60 times in the fi rst year (2004) aft er CC establishment relative to non-CC plots. At 66 kg N ha -1 , SH had no eff ects on sorghum yield, but it increased wheat yield in 2 of 3 yr. Cover crops increased soil total N pool by 270 kg ha -1 for the 0-to 7.5-cm depth. Crop yield increased with the CC-induced decrease in soil maximum compactibility (soil's susceptibility to compaction) and soil temperature, and increase in soil aggregate stability, soil organic carbon (SOC) and total N concentration, and soil water content, particularly at 0 kg N ha -1 . Principal component analysis (PCA) selected soil compactibility and total N as the best yield predictors. Inclusion of summer legume CCs in no-till fi xes N, increases crop yield, and improves soil-crop relationships.