The effects of cover crops on soil physical properties and nutrient cycling
Abstract
Cover crops improve soil aggregate stability, increase water infiltration, and legume cover crops also fix nitrogen and scavenge nutrients that are subject to leaching. Greenhouse and field experiments were conducted in Indiana to measure growth of different cover crops and their effects on soil properties. The objective of the greenhouse experiment was to study the response of three varieties of oilseed radish (Raphanus sativus) 'Groundhog', 'Maximus' and 'Terranova' to two soil bulk densities (1.15 and 1.45 g/cm 3) and two plant populations (50 and 163 plants/m2). The experiment was arranged as a randomized complete block design and was conducted in spring and repeated in fall 2010. The lower radish populations, compared to the higher population, had greater tuber length and diameter, greater total shoot and root N concentrations, and lower leaf dry weight and N mass per bucket. Radishes grown with higher soil bulk density had smaller shoot height and greater tuber diameter than when grown at the lower soil bulk density. Groundhog had greater leaf dry weight, greater tuber length, smaller tuber diameter, and higher shoot N mass compared to Maximus and Terranova, which did not differ from each other. Root N concentrations were higher in Maximus than the other varieties. The objective of the field experiment at the Agronomy Center for Research and Education (ACRE) was to evaluate the effects of different cover crops on soil aggregation, water infiltration rate, plant N and soil NO3 and NH4 concentrations. The experimental design was split-plot, with 4 blocks, two planting dates, six cover crop species including teff ( Eragrostis tef), pearlmillet (Pennisetum glaucum), hybrid sorghum sudangrass (Sorghum bicolor x S. bicolor var. Sudanese), oilseed radish (Raphanus sativus), cowpea (Vigna unguiculata), and non-dormant alfalfa (Medicago sativa), and the fallow control plot. On early planted plots, cowpea and sudangrass produced more biomass than the other treatments, and cowpea had the highest shoot N mass and concentration. On late planted plots, radish scavenged the same amount of N from a fertilizer application and residual soil N as was fixed and scavenged by cowpea. The study at ACRE showed that non-legume plots had higher soil NO3 and NH4 concentrations at the early sampling date due to fertilizer addition, but decreased over time due to N uptake by the cover crops. On the legume plots, soil NO3 concentrations increased over time due to nitrogen fixation. On the late planted plots, the control plot had higher NO3 concentrations than other treatments since there were no crops to scavenge soil N. Aggregate stability analyses in November on the early planted plots showed that grass cover crops had greater aggregate mean weight diameter (MWD) than other treatments, where teff had the greatest and control had the lowest aggregate MWDs. Aggregate analyses from the late planted plot showed that teff again had the greatest but radish and control plots had the lowest aggregate MWDs. The water infiltration rates were not affected by cover crops.
Degree
M.S.
Advisors
Kladivko, Purdue University.
Subject Area
Agronomy|Biogeochemistry|Soil sciences
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