531. Soil nitrate-nitrogen under tomato following tillage, cover cropping, and nitrogen fertilization

• Authors:
  • Singh, B. P.
  • Rahman, S.
  • Reddy, V. R.
  • Sainju, U. M.
• Source: Journal of Environmental Quality
• Volume: 28
• Issue: 6
• Year: 1999
• Summary: Management practices can influence NO3-N content and movement in the soil. We examined the influence of 3 yr of tillage [no-till (NT), chisel (CH), and moldboard (MB)], cover crop [hairy vetch (Vicia villosa Roth) (HV), and no hairy vetch (NHV)], and N fertilization (0, 90, and 180 kg N ha(-1)) on residual NO3-N content and movement on a Norfolk sandy loam (fine-loamy, siliceous, thermic, Typic Kandiudults) under tomato (Lycopersicon esculentum Mill) in central Georgia. Because of low N recovery by tomato, NO3-N content in the soil increased with depth, regardless of treatments, and ranged from 127 to 316 kg ha(-1) at 0- to 120-cm depth in the fall (September 1997). The content increased with increasing rate of N addition from cover crop residue and N fertilizer. From fall to spring (March 1998), 22 to 58% (37 to 129 kg NO3-N ha(-1)) of this content was lost, mostly due to leaching. Greater loss occurred in NT than in CH or MB, with HV than with NHV, and with 180 or 90 than with 0 kg N ha(-1). Similarly, greater loss at 0- to 60-cm than at 60- to 120-cm depth and significant correlation between soil NO3-N and clay concentration with depth indicates that NO3-N moved from the surface layer to the underlying clay layer, where it moved slowly. Nitrate-N content and movement in the soil from cover crop residue and N fertilizer were similar. Minimum tillage reduced NO3-N movement compared with NT, yet avoided the negative effects on soil and water quality associated with MB. Although HV increased tomato N uptake and recovery, it was not effective in reducing NO3-N content and movement com pared with N fertilizer.

532. Winter rye cover crop following soybean under conservation tillage: Residual soil nitrate

• Authors:
  • Walters, D. T.
  • Kessavalou, A.
• Source: Agronomy Journal
• Volume: 91
• Issue: 4
• Year: 1999
• Summary: Use of a winter rye (Secale cereale L.) cover crop following soybean [Glyceine max (L.) Merr.] has been shown to reduce the soil erosion potential in a corn (Zea mays L.)-soybean rotation system, but little is known about the effect of rye on residual soil NO(3)-N (RSN). An irrigated field study was conducted for 4 yr on a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudoll) to compare crop rotation and winter rye cover crop following soybean effects on RSN under several tillage practices and N fertilization rates. Treatments each gear were (i) tillage: no-till or disk; (ii) rotation: corn following soybean/rye (Cbr) or soybean/rye following corn (BRc), corn following soybean (Cb) or soybean following corn (Bc), and corn following corn (Cc); and (iii) N rate: 0, 100, and 300 kg N ha(-1) (applied to corn). Rye in the Cbr/BRc rotation was planted in the fall following soybean harvest and chemically killed in the spring of the following year prior to corn planting. Each spring, before tillage and N application, RSN was determined to a depth of 1.5 m, at 30-cm intervals. The net spring-to-spring change in RSN between subsequent spring seasons was computed for each plot, and annual aboveground N uptake for rye, corn, and soybean were determined. Rye, rotation, N rate, and tillage significantly influenced RSN in the top 1.5 m of soil. The presence of rye (BRc) reduced total spring RSN between 18 and 33% prior to corn planting in 2 of the 3 yr, compared with the no-rye system (Bc), as rye immobilized from 42 to 48 kg N ha(-1) in aboveground dry matter. Recycling of N in high-yielding rye cover crop residues led to an increase in RSN accumulation after corn in the succeeding spring. Up to 277 kg RSN ha(-1) accumulated at high rates of N following corn in the Cbr rotation, compared with 67 kg RSN ha(-1) in the no-rye system (Cb) in 1992. Regardless of the presence of rye, significant accumulation of RSN occurred following corn in the rotation sequence, while RSN declined following soybean. Less RSN was found in the top 1.5 m of soil under continuous than rotation corn, and disking tended to increase NO(3)(-) accumulation in rotation systems at high rates of N application. Although RSN declines following a rye cover crop, the ready release of this immobilized N suggests that some N credit should be given, reducing N recommendation for corn following winter rye cover, to minimize potential NO(3)(-) leaching under corn-soybean/rye rotations.

533. Rotational set-aside; influence of vegetation and management for one-year plant covers on soil mineral nitrogen during and after set-aside at five sites in England

• Authors:
  • Collins, C.
  • Chalmers, A. G.
  • Froment, M. A.
  • Grylls, J. P.
• Source: The Journal of Agricultural Science
• Volume: 133
• Year: 1999
• Summary: The effect of a range of one-year set-aside treatments on soil mineral nitrogen (SMN), during the set-aside period and in a following wheat crop were studied in a phased experiment at five sites from 1987 to 1991. Ground cover options permitted under the UK government's 'set-aside' scheme, including natural regeneration, autumn sown Italian ryegrass (Lolium multiflorum), spring-sown legumes and cultivated fallow, were compared with a control treatment of continuous cereals managed with fertilizer inputs. In the first of three phases in this experiment, an uncultivated fallow (kept weed-free) and autumn-sown forage rape (Brassica napus) were included as extra treatments. There were large differences in total SMN (0.0-0.9 m) between sites, ranging from 16 to 205 kg N/ha, reflecting differences in soil type, which ranged from clays to sands, and previous cropping husbandry. Differences in SMN between set-aside treatments during the first winter of the set-aside year were small, but increased during the following summer. Amounts of SMN were greatest after cultivated fallow (46-178 kg N/ha) and least after ryegrass (26-111 kg N/ha). Natural regeneration and spring sown legumes were more variable in their effect on SMN. Compared to continuous cereals, there was a build up in SMN during bare fallow, but a reduction under ryegrass, prior to returning to wheat cropping in the autumn after set-aside. SMN results suggest there was an increased nitrate leaching risk for bare fallow and natural regeneration set-aside, compared to sown ryegrass covers, in the winter following ploughing out of set-aside. This risk could be minimized by earlier sowing of winter cereals following set-aside or sowing with winter oilseed rape rather than cereals to maximize crop nitrogen (N) uptake, during the autumn growth period. Averaged across five sites, residual SMN supply in the spring of first test year cereal crops for all set-aside treatments was similar to that for continuous cereals, suggesting over-winter losses by N leaching or immobilization. The low residual N fertility after rotational set-aside suggested that following crop N recommendations should be the same as for continuous cereals. Amounts of SMN were less each year in spring than in the preceding autumn in both the set-aside and first test cereal crops. The results suggested that a ryegrass cover appeared to be the most environmentally favourable option for rotational set-aside management, as it minimized the amount of readily leachable N both during and immediately after the set-aside period.

534. Socio-economic determinants of soil conservation practices in Nigeria.

• Authors:
  • Bamire, A. S.
• Source: Indian Journal of Soil Conservation
• Volume: 27
• Issue: 3
• Year: 1999
• Summary: The socioeconomic determinants of soil conservation practices among small holder farmers in Delta State of Nigeria, were studied. Descriptive statistics, correlation analysis, budgetary and logit regression technique were employed as analytical tools to achieve the study objectives. Mulching was most common soil conservation practice in use while cover cropping was least in use. Crop rotation however, earned the highest net return while inorganic fertilizer earned least. The coefficients of correlation indicated that there were no exact linear relationships among the study variables. Results from logistic regression analysis showed that the level of education, farm size, mode of farmland acquisition, total farm returns and hired labour were statistically significant in explaining the probability of respondents' choice of soil conservation practices. These variables need be critically considered by policy makers when introducing or deciding on any new soil conservation practice. Extension education will, however, serve to guide farmers on the appropriate combination of conservation practices that could help derive the full synergistic benefits from their use. Adequate and timely supply of inorganic fertilizer would also assist respondents in the continuous use of their farmland for enhanced food production.

535. Changes in soil chemical properties resulting from organic and low-input farming practices

• Authors:
  • Scow, K. M.
  • Shennan, C.
  • Horwath, W. R.
  • Clark, M. S.
• Source: Agronomy Journal
• Volume: 90
• Issue: 5
• Year: 1998
• Summary: Soil chemical properties during the transition from conventional to organic and low-input farming practices were studied over 8 yr in California's Sacramento Valley to document changes in soil fertility status and nutrient storage. Four fanning systems differing in crop rotation and external inputs were established on land previously managed conventionally. Fertility in the organic system depended on animal manure applications and winter cover crops; the two conventional systems received synthetic fertilizer inputs; the low-input system used cover crops and animal manure during the first 3 yr and cover crops and synthetic fertilizer for the remaining 5 yr. At 4 and 8 yr after establishment, most changes in soil chemical properties were consistent with predictions based on nutrient budgets. Inputs of C, P, K, Ca, and Mg were higher in the organic and low-input systems as a result of manure applications and cover crop incorporations. After 4 yr, soils in the organic and low-input systems had higher soil organic C, soluble P, exchangeable K, and pH. Ceasing manure applications in the low-input system in Year 4 resulted in declining levels of organic C, soluble P, and exchangeable K. Crop rotation (the presence or absence of corn) also had a significant effect on organic C levels. Differences in total N appeared to be related in part to inputs, but perhaps also to differing efficiency of the farming systems at storing excess N inputs: the low-input system appeared to be most efficient, and the conventional systems were least efficient. Electrical conductivity (EC), soluble Ca, and soluble Mg levels were tightly linked but not consistently different among treatments. Relatively stable EC levels in the organic system indicate that animal manures did not increase salinity. Overall, our findings indicate that organic and low input farming in the Sacramento Valley result in small but important increases in soil organic C and larger pools of stored nutrients, which are critical for long-term fertility maintenance.

536. Measuring soil quality on the 'old rotation'.

• Authors:
  • Mitchell, C. C.,Jr.
  • Reeves, D. W.
  • Hubbs, M. D.
• Source: Proceedings 21st Annual Southern Conservation Tillage Conference for Sustainable Agriculture/Arkansas Agricultural Experiment Station Special Report 186
• Issue: 186
• Year: 1998
• Summary: Investigations were conducted on a Typic Hapludult in USA, to assess the effects of a 3 year rotation (cotton-grain crops plus a winter legume cover crop), a 2 year rotation (cotton-grain crops-winter legume), and 3 continuous cropping systems on soil quality after 100 years. Soil quality was better in the 3 year rotation plus legume cover crop. This was attributed to higher soil C, cation exchange capacity, water retention and water stable aggregates, and reduced surface soil strength. Under continuous cotton, soil strength was increased down to 5 in depth. N fertilizer and/or legume cover crop within continuous cotton increased soil C over the past 100 years. Because of continuous tillage over the 100 years the rotation treatments had little effect on soil extractable nutrients. The semi-quantitative assessment of the USDA-Soil Quality Kit gave higher variability of parameters relative to standard procedures. The Kit should therefore be used only to evaluate trends and comparisons.

537. Long-term evaluation of cover crop and strip-tillage on tomato yield, foliar diseases and nematode populations

• Authors:
  • Potter, J. W.
  • Cerkauskas, R. F.
  • McKeown, A. W.
  • Van Driel, L.
• Source: Canadian Journal of Plant Science
• Volume: 78
• Issue: 2
• Year: 1998
• Summary: A 6-yr (1987-1992) experiment, continuous on the same site, evaluated potential problems for yield, nematodes and diseases with tomatoes (Lycopersicon esculentum Mill.) grown in a strip-till system. Treatments consisted of conventional tillage (CT) and strip tillage (ST), rye (Secale cereale L.), wheat (Triticum aestivum L.) and perennial ryegrass (Lolium perenne L.) cover crops and a 2-yr rye-tomato rotation. Results of the first 5 yr indicated a decrease in tomato yield over time for both tillage treatments and cover crops. However, yield rebounded overall for treatments in 1992 with the highest yield in the rye-tomato rotation. We suspect this was a result of high populations of root-knot nematodes which collapsed over the winter of 1991/1992. Tomato yields were lower following wheat and perennial ryegrass than rye. In only 1 yr out of 6, strip-tillage reduced yield compared with conventional tillage. Bacterial speck/spot symptoms on foliage, although minor, were significantly greater in ST than in CT plots during the last 3 yr. No major trends in incidence and severity of bacterial and fungal diseases and of disorders of fruit were evident during the 5-yr period and neither fruit yield nor quality were significantly affected by these factors. Root-knot nematodes (Meloidogyne hapla Chitwood) were numerically less in the rye-tomato rotation than in other treatments; both root-knot and root lesion nematodes (Pratylenchus penetrans [Cobb]) tended to be less numerous under CT than under ST. Strip-tillage is feasible for machine harvest processing tomatoes. However, we are concerned about the tendency of tomatoes grown under reduced tillage to have lower yields than those grown under conventional tillage. More work is required on the interactions of cultivars, cover crops and nematodes in soil conservation systems.

538. No-till farming: The way of the future for a sustainable dryland agriculture

• Authors:
  • Papendick, R.
  • Parr, J.
• Source: Annals of Arid Zone
• Volume: 36
• Issue: 3
• Year: 1997
• Summary: Most dryland fanning systems depend an tillage to grow crops. There is overwhelming evidence that repeated tillage is destroying the soil resource base and causing adverse environmental impacts. Tillage degrades the fertility of soils, causes air and water pollution, intensifies drought stress, destroys wildlife habitat, wastes fuel energy, and contributes to global warming. Consequently, most tillage-based systems in a dryland environment are not sustainable in the long-term. Today, dryland farmers are expected to produce food in ever greater quantities. This is becoming more difficult to do in view of declining soil quality, most of which is caused by soil tillage. It is becoming well documented scientifically that continuous no-till is the most effective, and practical approach for restoring and improving soil quality which is vital for sustained food production and a healthy environment. With this way of farming crop, residues or other organic amendments are retained on the soil surface and sowing/fertilizing is done with minimal soil disturbance. Research and farmers' experience indicate that with continuous no-till soil organic matter increases, soil structure improves, soil erosion is controlled, and in time crop yields increase substantially from what they were under tillage management, due to improved water relations and nutrient availability. These changes help to promote a cleaner and healthier environment and a more sustainable agriculture. A major obstacle that farmers often face with change to continuous no-till is overcoming yield-limiting factors during the transition years, that is, the first years of no-till following a history of intensive conventional tillage. These factors are often poorly understood and may be biologically-driven. Some of the problems involve residue management and increased weed and disease infestations. Farmer experience seems to indicate that many problems during the transition are temporary and become less important as the no-till system matures and equilibrates. The judicious use of crop rotations, cover crops and same soil disturbance may help reduce agronomic risks during the transition years. Farmers switching to continuous no-till must often seek new knowledge and develop new skills and techniques in order to achieve success with this new and different way of farming. Answers to their questions are urgently needed to provide strategies far promoting no-till as a way to enhance agricultural sustainability for future generations.

539. Agricultural soils as a sink to mitigate CO2 emissions

• Authors:
  • Woomer, P. L.
  • Noordwijk, M.
  • Tiessen, H.
  • Tian, G.
  • Smith, P.
  • Lal, R.
  • Janzen, H. H.
  • Andrén, O.
  • Paustian, K.
• Source: Soil Use and Management
• Volume: 13
• Year: 1997
• Summary: Agricultural soils, having been depleted of much of their native carbon stocks, have a significant CO2 sink capacity. Global estimates of this sink capacity are in the order of 20-30 Pg C over the next 50-100 years. Management practices to build up soil C must increase the input of organic matter to soil and/or decrease soil organic matter decomposition rates. The most appropriate management practices to increase soil C vary regionally, dependent on both environmental and socioeconomic factors. In temperate regions, key strategies involve increasing cropping frequency and reducing bare fallow, increasing the use of perennial forages (including N-fixing species) in crop rotations, retaining crop residues and reducing or eliminating tillage (i.e. no-till). In North America and Europe, conversion of marginal arable land to permanent perennial vegetation, to protect fragile soils and landscapes and/or reduce agricultural surpluses, provides additional opportunities for C sequestration. In the tropics, increasing C inputs to soil through improving the fertility and productivity of cropland and pastures is essential. In extensive systems with vegetated fallow periods (e.g. shifting cultivation), planted fallows and cover crops can increase C levels over the cropping cycle. Use of no-till, green manures and agroforestry are other beneficial practices. Overall, improving the productivity and sustainability of existing agricultural lands is crucial to help reduce the rate of new land clearing, from which large amounts of CO2 from biomass and soil are emitted to the atmosphere. Some regional analyses of soil C sequestration and sequestration potential have been performed, mainly for temperate industrialized countries. More are needed, especially for the tropics, to capture region-specific interactions between climate, soil and management resources that are lost in global level assessments. By itself, C sequestration in agricultural soils can make only modest contributions (e.g. 3-6% of total fossil C emissions) to mitigating greenhouse gas emissions. However, effective mitigation policies will not be based on any single 'magic bullet' solutions, but rather on many modest reductions which are economically efficient and which confer additional benefits to society. In this context, soil C sequestration is a significant mitigation option. Additional advantages of pursuing strategies to increase soil C are the added benefits of improved soil quality for improving agricultural productivity and sustainability.

540. Short-term effects of cover crop incorporation on soil carbon pools and nitrogen availability

• Authors:
  • Demment, M. W.
  • Shennan, C.
  • Drinkwater, L. E.
  • van Bruggen, A. H. C.
  • Gamble, G. R.
  • Grunwald, N. J.
  • Hu, S.
• Source: Soil Science Society of America Journal
• Volume: 61
• Issue: 3
• Year: 1997
• Summary: Winter cover crops are increasingly used to maintain water quality and agroecosystem productivity. Cover crop incorporation influences transient soil microbial dynamics and nutrient availability at an early growth stage of subsequent crops. Short-term ([35 <= d) effects of cover crop incorporation on soil C pools and N availability were evaluated using sandy loam soils from organically and conventionally managed fields. Field and incubation experiments were designed to investigate whether cover crop incorporation had differential effects on C pools and how they were related to N mineralization. Labile C pools (soil carbohydrates and soil microbial biomass C [SMBC]) and coarse organic debris (COD) increased two- to threefold, whereas total organic C increased by only 20% by Day 7 after incorporation. The COD decreased faster than other C pools and best predicted SMBC (P 30% of N in cover crop residues was mineralized in both soils by Day 35 after incorporation, suggesting that manipulations of soil microbial dynamics and N mineralization in the short term can be of particular significance in synchronizing N release with the need of subsequent crops.