Soil fertility and crop yields in long-term organic and conventional cropping systems in Eastern Nebraska

Abstract

Organic agriculture aims to build soil quality and provide long-term benefits to people and the environment; however, organic practices may reduce crop yields. This long-term study near Mead, NE was conducted to determine differences in soil fertility and crop yields among conventional and organic cropping systems between 1996 and 2007. The conventional system (CR) consisted of corn (Zea mays L.) or sorghum (Sorghum bicolor (L.) Moench)-soybean (Glycine max (L.) Merr.)-sorghum or corn-soybean, whereas the diversified conventional system (DIR) consisted of corn or sorghumsorghum or corn-soybean-winter wheat (wheat, Triticum aestivum L.). The animal manure-based organic system (OAM) consisted of soybean-corn or sorghum-soybean-wheat, while the forage-based organic system (OFG) consisted of alfalfa (Medicago sativa L.)-alfalfa-corn or sorghum-wheat. Averaged across sampling years, soil organic matter content (OMC), P, pH, Ca, K, Mg and Zn in the top 15 cm of soil were greatest in the OAM system. However, by 2008 OMC was not different between the two organic systems despite almost two times greater carbon inputs in the OAM system. Corn, sorghum and soybean average annual yields were greatest in either of the two conventional systems (7.65, 6.36 and 2.60 Mg ha -1 , respectively), whereas wheat yields were greatest in the OAM system (3.07 Mg ha -1 ). Relative to the mean of the conventional systems, corn yields were reduced by 13 and 33% in the OAM and OFG systems, respectively. Similarly, sorghum yields in the OAM and OFG systems were reduced by 16 and 27%, respectively. Soybean yields were 20% greater in the conventional systems compared with the OAM system. However, wheat yields were 10% greater in the OAM system compared with the conventional DIR system and 23% greater than yield in the OFG system. Alfalfa in the OFG system yielded an average of 7.41 Mg ha -1 annually. Competitive yields of organic wheat and alfalfa along with the soil fertility benefits associated with animal manure and perennial forage suggest that aspects of the two organic systems be combined to maximize the productivity and sustainability of organic cropping systems.

First‐Season Crop Yield Response to Organic Soil Amendments: A Meta‐Analysis

“…However, using fresh animal manures to meet all crop nutrient demands can increase groundwater nitrate leaching and surface runoff of P (Kleinman et al, 2002;Basso and Ritchie, 2005). In most cases, it is not recommended that farmers use manure alone to meet crop N demand because over time P will accumulate well beyond crop sufficiency levels and potentially contribute to pollution of surface waters (Wortman et al, 2012a). Instead, best management practices for calculating organic soil amendment rates should include consideration of N/P ratio of the amendment, baseline soil nutrient levels, crop nutrient demands, and potential mineralization rate of the amendment.…”

“…Manure and compost application to arable soils can lead to long-term increases in plant essential nutrients (e.g., P, K, and Mg; Bulluck et al, 2002;Wortman et al, 2012a), soil organic matter content, aggregate stability, and water-holding capacity (Goyal et al, 1999;Diacono and Montemurro, 2010), and microbial abundance and activity (Goyal et al, 1999;Pérez-Piqueres et al, 2006). Crop yield can also increase over time with regular application of manure or compost to the same fi eld (Jiang et al, 2006), and yields are oft en similar between fi elds with a long-term history of organic soil amendment compared to inorganic fertilization (Edmeades, 2003).…”

Environmental impacts of organic agriculture in temperate regions.

“…This was reflected in improved soil productivity under the organic plots. Wortman et al [23] report a long-term (11-year) cropping systems study in Nebraska, in which the conventional system consisted of fertilized soybean, winter wheat, maize and sorghum, while organic systems utilized composted beef manure (applied once only) in place of fertilizer, or an alfalfa forage, prior to maize and sorghum. At the end of the study (SOC levels were reported for 0-15 cm depth only) treatments had largely equivalent SOC concentrations.…”

“…Indeed as a reflection of this reality on many organic, particularly grain farms, in North America, long-term rotation studies, such as that of Wortman et al [83] (Nebraska); [Entz, personal communication, 2011] (Manitoba); and Lynch et al [106] (Nova Scotia), tend to use manure or compost supplements as an intermittent P source rather than as a routine N source. For example, Wortman et al [23] in Nebraska used composted beef manure (~30 Mg/ha applied once in 11 years) to offset potential P deficiencies in their organic perennial-grains cropping system. While novel organic amendments such as source-separated municipal solid waste (or 'green waste') composts may be an effective source of soil P (and N) supply [106,123], their use remains limited at present.…”

“…Often, organic yields average 20% below conventional crop and livestock production systems, respectively [19][20][21][22][23][24]. However, the yield difference depends on the crops, the farming system, the degree of intensification in local conventional farming and agro-ecological conditions [25].…”