Soil Health, Phosphorus and Carbon Dynamics in Response to a One-Time Compost Application and Cover Crops in Organic Dryland Winter Wheat

Organic dryland winter wheat (Triticum aestivum) growers in the U.S. are faced with high interannual variability in yields. This is related to the low annual precipitation and low soil fertility on the cultivated soils. Improving soil health is the key to increasing and maintaining crop yields. In this study, we compared the effects of different rates (0, 12.5, 25 and 50 Mg DW ha-1 compost and 2 Mg ha manure-1) of large quantities of steer manure compost and the inclusion of cover crops versus fallow on soil health and on carbon and phosphorus dynamics in two organic dryland systems with varying soil characteristics and microclimatic conditions. The two sites are located in Snowville and Blue Creek, Utah. At Snowville, the soil fertility is extremely low, pH is 8.5, and average total annual precipitation is 290 mm. At Blue Creek, the soil is more fertile, pH is 7.2 and average total annual precipitation is 485 mm. The results showed that the compost effect on measured physical, biological and chemical soil health indices (soil moisture, dehydrogenase and phosphatasesenzyme activities, soil organic carbon, Olsen P) were greater than the effects of cover crops at both sites. Differences were also found in phosphorus cycling between the two sites, with potential long-term impacts in soils with extreme low fertility due to lower rate of nutrient mineralization. By applying large quantities of compost (25-50 Mg DW ha-1) once, organic dryland winter wheat farmers can improve soil health, enhance SOM associated water retention and availability, and provide an environment for continuous sustainable wheat yield

Effects of a one-time compost addition on soil health in a rainfed dryland organic wheat system

Maintaining adequate soil fertility and health is a challenge in dryland organic wheat systems. This research examines the short-term impact of a one-time addition of compost on the soil health in a rainfed dryland organic winter-wheat (Triticum aestivum L.) fallow system. Field plot experiments were established in 2015 in a semiarid dryland organic wheat field in Snowville, Utah with the following treatments: control (C), compost at 12.5 Mg/ha dry weight (CM1), 25 Mg/ha (CM2), 50 Mg/ha (CM3), positive control 25 Mg compost + 40 lb N feather meal (PC), and 2 Mg chicken manure (CMU). Soil samples were taken in May 2016 at a depth of 0-10 cm from the plots in the wheat phase of the rotation. Indicators of soil health and fertility were determined such as microbial biomass C, enzyme activities involved in the cycling of C and P, total organic carbon and nitrogen determined. The application of compost appeared to promote microbial activities with the greatest effect at CM3. Acid and alkaline phosphatase enzyme activities significantly increased by as much as 61 % and 47 % respectively. Microbial biomass carbon, dehydrogenase enzyme activity, readily mineralizable carbon, total organic carbon and total nitrogen were highest at CM3. Based on our findings so far, compost addition stimulated soil microbial activities and boosted organic C and N in the surface layers of the soil. Outcomes of this study will contribute to the overall goal of enhancing productivity and sustainability of rainfed dryland organic winter-wheat

Soil aggregation and phosphorus availability following a one-time compost addition in semi-arid organic wheat systems

The addition of compost can enhance soil aggregation and phosphorus availability in dryland organic wheat systems where yields are severely constrained. Increase in soil aggregation can reduce nutrient loss and increase crop yield. The aim of this work was to examine the effect of a one-time compost addition on soil aggregation and phosphorus (P) availability across two semi-arid organic wheat systems with varying characteristics. Compost was applied to two semi-arid organic wheat systems at the rates of 0, 25, and 50 Mg ha-1. The first site is known to have high calcium carbonate content and lower annual precipitation (SN), while the second site has a low calcium carbonate content and higher annual precipitation. Bulk soil was separated into four aggregate-size fractions (\u3e 2000 μm large macroaggregates; 2000–250 μm small macroaggregates;\u3c 250 μm microaggregates). Forms of bioavailable P pools were investigated. Compost addition significantly enhanced the soil aggregation at the SN site but not at the BC site. The addition of compost enhanced the formation of macroaggregates at SN. Soil phosphorus availability was significantly enhanced at both sites. However, the impact of compost addition on bioavailable phosphorus forms was higher at SN than at BC. These results provide evidence that the impact of compost on soil characteristics varies across different dryland organic wheat systems