An econometric investigation of impacts of sustainable land management practices on soil carbon and yield risk: A potential for climate change mitigation

We investigate the impacts of sustainable land management practices on soil carbon stocks and also impacts of soil carbon on the mean and variance of crop production using econometric tools. Using a cross-sectional plot-level dataset collected from three agroecological zones of Uganda with soil carbon measured at a depth of 0 to 15 centimeters, our results have robustly shown that irrigation, fertilizers, improved fallow, crop residues, mulching, and trash lines are positively and significantly associated with higher soil carbon, corroborating results from agronomic experiments. However, we found crop rotation associated with lower soil carbon, which has also been observed in some agronomic experiments. Soil carbon has shown a significant nonlinear effect on crop production with the threshold occurring at 29.96 milligrams of carbon per hectare, above which farmers start to see significant positive effects on crop production. Furthermore, we found soil carbon to be associated with lower variance of crop production; hence, soil carbon is an indicator of crop yield loss risk (soil carbon has a risk-reducing effect). These empirical results have demonstrated strong evidence for developing countries of the potential of sustainable land management practices to enhance carbon sequestration and also the potential of soil carbon to reduce production risk. The results have implications for the role that soil carbon can play in adaptation to climate change and provision of ecosystem services.Land management, Climate change, soil carbon, Production risk, Carbon sequestration, Just and Pope stochastic production function,

Effects of vertical distribution of soil inorganic nitrogen on root growth and subsequent nitrogen uptake by field vegetable crops

Information is needed about root growth and N uptake of crops under different soil conditions to increase nitrogen use efficiency in horticultural production. The purpose of this study was to investigate if differences in vertical distribution of soil nitrogen (Ninorg) affected root growth and N uptake of a variety of horticultural crops. Two field experiments were performed each over 2 years with shallow or deep placement of soil Ninorg obtained by management of cover crops. Vegetable crops of leek, potato, Chinese cabbage, beetroot, summer squash and white cabbage reached root depths of 0.5, 0.7, 1.3, 1.9, 1.9 and more than 2.4 m, respectively, at harvest, and showed rates of root depth penetration from 0.2 to 1.5 mm day)1 C)1. Shallow placement of soil Ninorg resulted in greater N uptake in the shallow-rooted leek and potato. Deep placement of soil Ninorg resulted in greater rates of root depth penetration in the deep-rooted Chinese cabbage, summer squash and white cabbage, which increased their depth by 0.2–0.4 m. The root frequency was decreased in shallow soil layers (white cabbage) and increased in deep soil layers (Chinese cabbage, summer squash and white cabbage). The influence of vertical distribution of soil Ninorg on root distribution and capacity for depletion of soil Ninorg was much less than the effect of inherent differences between species. Thus, knowledge about differences in root growth between species should be used when designing crop rotations with high N use efficiency

BLACK POLYPROPYLENE MULCH TEXTILE IN ORGANIC AGRICULTURE

Black polyethylene mulch is used for weed control in a range of crops under the organic system. The use of black polypropylene mulch is usually restricted to perennial crops. The trial was conducted at Experimental station of Department of Crop Production of the Czech University of Life Science Prague-Uhříněves in Czech Republic. For the experiments were used black polypropylene woven mulch (comparison wit bare soil), two varieties of early potatoes Finka and Katka. Black polypropylene textile was used in potatoes by organic agriculture and it had positive effect on soil temperature (in the depth of 100 mm). Slightly higher soil temperatures under black polypropylene mulch in the vegetation period after planting had favourable influence on earlier stands emergence. The soil water potential (in the depth of 250 mm) and also the soil water content have been beneficial for black polypropylene mulch. Significantly lower values of the soil water potentials have been found in the period after planting and at the end of vegetation. Black polypropylene mulch provided favourable temperatures and soil moisture. Post harvest analyses were focused on the determination of the yield and quality tubers from each variant

Tine options for alleviating compaction in wheelings

Repeated trafficking and harvesting operations lead to high levels of compaction in inter-row wheelings used in asparagus (Asparagus officinalis) production. This reduces soil porosity and infiltration resulting in water ponding on the soil surface. Even on gently sloping land this can result in runoff generation and an increased risk of soil erosion. A winged tine (WT) is currently used by a leading asparagus grower to loosen compacted inter-row wheelings. In order to test the effectiveness of this tine for alleviating compaction and implications for runoff and soil erosion control, it was evaluated alongside several other tine configurations. These were a narrow tine (NT); a narrow tine with two shallow leading tines (NSLT); a winged tine with two shallow leading tines (WSLT); and a modified para-plough (MPP). Testing was conducted under controlled conditions on a sandy loam soil in the Soil Management Facility at Cranfield University, Bedfordshire, UK. Tine performance was assessed at 3 depths (175, 250 and 300 mm) by draught force; soil disturbance (both above and below ground); specific draught for a given level of soil disturbance; surface roughness; and estimated change in soil bulk density. The effectiveness of tines for compaction alleviation and potential for mitigating runoff and soil erosion varied with depth. The most effective tines were found to be the MPP NSLT and the WSLT at 175 mm, 250 mm and 300 mm depth, respectively

Infiltration and short-term movement of nitrogen in a silt-loam soil typical of rice cultivation in Arkansas

Rice production in Arkansas is one of the top three crop commodities in terms of cash receipts. Researchers and farmers report that nitrogen (N) needs to be managed according to a variety of factors with two important ones being soil and fertilizer type. The objectives of this experiment were to determine: 1) the degree to which floodwater-incorporated N applied as urea or as ammonium sulfate infiltrates intact cores (7.2-cm dia., 10-cm depth) containing DeWitt siltloam soil, and 2) the distribution of N during 12 h of ponding. Inorganic-N concentrations were analyzed at 2-cm depth intervals in cores following removal of the flood. Nitrogen from applied fertilizer was recovered as ammonium. Ammonium sulfate-N remained in the top 4 cm of soil with concentrations of 375 µg N g-1 in the surface 2 cm and 300 µg N g-1 at the 2 - 4 cm depth after 12 hr of ponding. At all depth intervals below 4 cm, ammonium sulfate-N remained below 30 µg N g-1. In contrast, after 12 h of ponding, N in soil receiving urea was 105 µg N g-1 in the top 2 cm and 173 µg N g-1 at 2-4 cm. At 4-6, 6-8, and 8-10 cm, N was 109, 108, and 35 µg N g-1, respectively, after 12 h of ponding. These results demonstrate immediate and deeper movement of ammonium into silt loam soil receiving urea as compared to ammonium sulfate, demonstrating how the form of N in fertilizer affects its movement into the soil profile

Influence of chemical denudation on hillslope morphology

[1] Models of hillslope evolution involving diffusion-like sediment transport are conventionally presented as an equation in which the changes in land-surface elevation or soil thickness are balanced by the divergence of soil transport and tectonic uplift, soil production, or both. These models typically do not include the loss or gain of mass in hillslope soils due to processes of chemical weathering and deposition. We formulate a more general depth-integrated equation for the conservation of soil mass on a hillslope that includes a term representing chemical deposition or denudation. This general depth-integrated equation is then simplified to determine the one-dimensional form of a steady state hillslope which experiences both mechanical and chemical denudation. The differences in morphology between hillslopes only experiencing diffusion-like mechanical sediment transport and hillslopes experiencing both diffusion-like mechanical sediment transport and chemical denudation are explored. Under the conditions of a downslope increase in local soil lowering rate due to chemical weathering the hillslope profile will depart from the parabolic shape predicted by models that incorporate only linear diffusion-like mechanical sediment transport. In addition, hillslopes that experience both chemica

Modelling diverse root density dynamics and deep nitrogen uptake — a simple approach

We present a 2-D model for simulation of root density and plant nitrogen (N) uptake for crops grown in agricultural systems, based on a modification of the root density equation originally proposed by Gerwitz and Page in J Appl Ecol 11:773–781, (1974). A root system form parameter was introduced to describe the distribution of root length vertically and horizontally in the soil profile. The form parameter can vary from 0 where root density is evenly distributed through the soil profile, to 8 where practically all roots are found near the surface. The root model has other components describing root features, such as specific root length and plant N uptake kinetics. The same approach is used to distribute root length horizontally, allowing simulation of root growth and plant N uptake in row crops. The rooting depth penetration rate and depth distribution of root density were found to be the most important parameters controlling crop N uptake from deeper soil layers. The validity of the root distribution model was tested with field data for white cabbage, red beet, and leek. The model was able to simulate very different root distributions, but it was not able to simulate increasing root density with depth as seen in the experimental results for white cabbage. The model was able to simulate N depletion in different soil layers in two field studies. One included vegetable crops with very different rooting depths and the other compared effects of spring wheat and winter wheat. In both experiments variation in spring soil N availability and depth distribution was varied by the use of cover crops. This shows the model sensitivity to the form parameter value and the ability of the model to reproduce N depletion in soil layers. This work shows that the relatively simple root model developed, driven by degree days and simulated crop growth, can be used to simulate crop soil N uptake and depletion appropriately in low N input crop production systems, with a requirement of few measured parameters

Empirical Models for Predicting Soil-Climate and Related Pasture Grass Preformance in Maui, Hawaii (An Evaluation of Soil-Climate Criteria of Soil Taxonomy)

Soil Taxonomy requires soil-climate for soil classification and the interpretation of the relationships between soil, climate, and plant. The depth at which soil temperature and soil moisture regimes are currently measured or estimated have been, however, given without presenting any evidence of any particular importance of soil-climate at these depths to soil genesis and/or plant growth. The objectives of this study were to develop mathematical models that can provide first approximations of soil temperatures at different depths and evaluate the depth at which soil temperature and/or soil moisture correlate most to herbage production. Such a knowledge can be used as a criterion for better identification of soil-climate and serve as a basis for the evaluation of the current soil-climate criteria of Soil Taxonomy. Located on the island of Maui, Hawaii, the area of the study extended along a climosequence with a wide range of ecological zones. The altitudes vary from 36 to 1620 m, the soils from Inceptisols (Andepts) to Mollisols and Oxisols, mean annual air temperatures from 13 to 24 °c, and total mean annual precipitation from 100 to 872 mm. Computerized automatic weather stations were installed to monitor air and soil-climate environment at 11 sites and pasture grass growth was observed at four of the sites. The measurements included air temperature, soil temperatures at 0.1- and 0.5- m depths, soil moisture at 0.1- and 0.5-m depths, relative humidity, rainfall, and solar radiation. The dominant grass species were buffel grass, kikuyu grass, and an admixture of fescue, sweet vernal, rattail, Yorkshire fog, and white clover. Simple linear, multiple, and quadratic regression models were developed to estimate the soil temperatures at 0.1- and 0.5-m depths from air temperature and other environmental factors. All of the models showed a satisfactory coefficient of determination, but the quadratic models were judged to have a greater predictive ability than the others because of their slightly higher R2 and smaller residual mean squares. In addition, the quadratic models depicted better the curvilinear relationship between the air and soil temperatures. Soil temperatures predicted by the quadratic models were in better agreement with the measured temperatures than those predicted by the model currently used in Soil Taxonomy. A modification of the Soil Taxonomy model is proposed for soil temperature, that is, to add 2 °c to the air temperature if the air temperature is less than 22 °c or to add 4 °c if the air temperature is equal to or greater than 22 °c. Such a modification gives a close approximation of the measured soil temperature at 0.5-m depth. Seasonal fluctuations of herbage production were more correlated to soil-climate at 0.5-m depth than to atmospheric weather or soil-climate at 0.1-m depth. The-use of soil-climate properties in Soil Taxonomy is, therefore, justified. The greater impact of soil moisture at 0.5-rn depth suggests the location of the soil moisture control section at or below that depth, regardless of soil texture. It is concluded that if Soil Taxonomy is to be a basis of prognosis of plant response to soil, soil-climate, and other crop production parameters, the diagnostic criteria of soil-climate at 0.5-m depth best serve the purpose