Antecedent water content effects on runoff and sediment yields from two Coastal Plain Ultisols

The highly weathered, low-carbon, intensively cropped, drought-prone Coastal Plain soils of Georgia are susceptible to runoff and soil loss, especially at certain times of the year when soil water contents are elevated. We quantified the effects of antecedent water content (AWC) on runoff (R) and sediment (E) losses from two loamy sands managed under conventional- (CT), strip- (ST), and/or no-till (NT) systems. Two AWC treatments were evaluated: field moist (FM) and pre-wet (PW), created with and without post pesticide application irrigations (∼12 mm of water added with the rainfall simulated over 30 min) for incorporation. Treatments (5) evaluated were: CT + FM, CT + PW, ST + FM, ST + PW, and NT + PW. Field plots, each 2-m × -3 m, were established on each treatment. Each 6-m² field plot received simulated rainfall at a variable rainfall intensity (I_v) pattern for 70 min (site 1) or a constant rainfall intensity (I_c) pattern for 60 min (site 2; I_c = 50.8 mm h⁻¹). Adding ∼12 mm of water as herbicide incorporation increased AWCs of the 0-2 (3-9-fold) and 2-15 (23-117%) cm soil depths of PW plots compared to existing field moist soil conditions. Increase in AWC increased R (as much as 60%) and maximum R rates (as much as 62%), and decreased E (at least 59%) and maximum E rates (as much as 2.1-fold) for corresponding tillage treatments. Compared to CT plots, ST and NT plots decreased R (at least 2.6-fold) and maximum R rates (as much as 3-fold), and decreased E (at least 2.7-fold) and maximum E rates (at least 3.2-fold). Runoff curves for pre-wetted CT and ST plots were always higher than corresponding FM curves, whereas E curves for field moist CT and ST plots were always higher than corresponding PW curves. Changes in AWC and tillage affected detachment and transport processes controlling runoff and sediment yields. A more accurate measure of rainfall partitioning and detachment and transport processes affecting R and E losses was obtained when commonly occurring field conditions (increased AWC with irrigation; I_v pattern derived from natural rainfall; commonly used tillage systems) were created and evaluated.     

Quantifying rainfall-runoff relationships on the Dera Calcic Fluvic Regosol ecotope in Ethiopia

Droughts, resulting in low crop yields, are common in the semi-arid areas of Ethiopia and adversely influence the well-being of many people. The objective of this study was to assess the benefit that in-field rainwater harvesting (IRWH) would have, compared to conventional tillage, on maize yields on a semi-arid ecotope at Dera situated on the eastern part of the Rift Valley. Rainfall-runoff measurements were made during 2003 and 2004 on 2 m × 2 m plots provided with a runoff measuring system and replicated three times for each treatment. There were two treatments: conventional tillage (CT) and no-till (NT), the latter with a flat surface that promotes runoff and therefore IRWH. Rainfall intensity was measured at 1 min intervals with an automatic tipping bucket instrument, and runoff was measured after each rain event. Measured runoff as a function of rainfall intensity and duration from half the rainfall-runoff events was used to determine the critical parameters of a appropriate runoff model. The calibrated model was found to be capable of predicting runoff in a satisfactory way.Rainfall-runoff measurements were made during the rain seasons in 2003 and 2004 during which there were 25 rain events with >9 mm of rain. There was no statistical difference between the runoff on the two treatments. The measured runoff (R) for the two rain seasons, expressed as a fraction of the rainfall during the measuring period (P), i.e. R/P, gave values of 0.46 and 0.39 for the NT and CT treatments, respectively.Results from 7 years of field experiments with IRWH at Glen in South Africa were used to estimate the yield benefit of NT for Dera compared to CT. The results were 696 and 494 kg ha⁻¹ for 2003 and 2004, respectively. Based on the estimated average long-term maize yield of 2000 kg ha⁻¹ at Dera, this was an estimated yield increase ranging from 25% to 35%.     

Field evaluation of sand-ditch water harvesting technique in Jordan

Water harvesting is viable alternatives for rainfed agricultural production in semiarid lands. A field experiment was conducted to evaluate the efficiency of a relatively new water harvesting technique, called sand ditch, for moisture and soil conservation. Twelve field plots of 10 m × 2 m were constructed in two adjacent fields having silt loam soils but varied in soil depth, 0.75 m and 2 m, and slope of 10% and 12%. A 130 L barrel was installed at the downslope end of the plots to collect water and sediments at the end of each rainstorm along the rainy season. Three types of treatments were used in duplicates (12 plots in total); sand-ditch plots in which a ditch of 2-m long, 1 m wide and 0.8 m deep was constructed in the middle of plots across the slope (2 in each field), two compacted plots and two plots covered with plastic mulch in addition to four control plots, 2 in each field. The total amount of runoff, sediment concentration, total infiltration and sediment loss for the experimental plots were measured or calculated after each storm during the winter season 2004/2005. Experimental results showed that sand-ditch technique significantly reduced runoff and sediment loss and increased infiltration and soil moisture compared to control or compacted plots. The overall average runoff and sediment reductions in the sand-ditch plots were 46% and 61% compared to control plots. Sediment losses from compacted plots were about 2.2 and 6 folds higher than control and sand-ditch plots, respectively making soil compaction unsuitable technique for rainfall harvesting under the current experimental and climatic conditions. Construction of sand ditch also increased the dry matter yield of native grass by an average of 62% and 40% in the two experimental fields compared to control.     

Furrow diking in conservation tillage

Crop production in the Southeastern U.S. can be limited by water; thus, supplemental irrigation is needed to sustain profitable crop production. Increased water capture would efficiently improve water use and reduce supplemental irrigation amounts/costs, thus improving producer's profit margin. We quantified infiltration (INF), runoff (R), and sediment (E) losses from furrow diked (+DT) and non-furrow diked (−DT) tilled conventional (CT) and strip tillage (ST) systems. In 2008, a field study (Tifton loamy sand, Typic Kandiudult) was established with DT, ST, and CT systems. In 2009, a field study (Faceville loamy sand, Typic Kandiudult) was established with DT and ST systems. Treatments (6) included: CT − DT, CT + DT, ST₁ (1-year old) − DT, ST₁ + DT, ST₁₀ (10-year old) − DT, and ST₁₀ + DT. Simulated rainfall (50 mm h⁻¹ for 1 h) was applied to each 2-m × 3-m plots (n = 3). Runoff and E were measured from each 6-m² plot. ST₁ + DT plots had 80-88% less R than ST₁ − DT plots. Any disturbance associated with DT in ST₁ systems did not negatively impact E values. For both soils, CT − DT plots represented the worst-case scenario in terms of measured R and E; ST + DT plots represented the best-case scenario. Trends for R, E, and estimated plant available water (PAW) values decreased in order of CT − DT, CT + DT, ST₁ − DT, ST₁ + DT, ST₁₀ − DT, and ST₁₀ + DT treatments. From a hydrology standpoint, ST₁ − DT plots behaved more similarly to CT plots than to other ST plots; from a sediment standpoint, ST₁ − DT plots behaved more similarly to other ST plots than to CT plots. DT had no effect on ST₁₀ plots. CT − DT and ST₁₀ + DT plots resulted in 5.9 (worst-case) and 8.1 (best-case) days of water for crop use, a difference of 2.2 days of water for crop use or 37%. Compared to the CT − DT treatment, an agricultural field managed to CT + DT, ST₁ − DT, ST₁ + DT, ST₁₀ − DT, and ST₁₀ + DT would save a producer farming the CT − DT field $5.30, $9.42, $13.55, $14.14, and $14.14 ha⁻¹, respectively, to pump the amount of water lost to R and not saved as INF back onto the field. The most water/cost savings occurred for CT and ST₁ plots as a result of DT. Savings for CT + DT, ST₁ − DT, and ST₁ + DT treatments represent 27%, 47%, and 68% of the cost of DT ($20 ha⁻¹) and 37%, 67%, and 96% of the savings a producer would have if managing the field to ST for 10 years without DT (ST₁₀ − DT) in a single 50-mm rainfall event. For row-crop producers in the Southeastern U.S. with runoff producing rainfall events during the crop growing season, DT is a management practice that is cost-effective from a natural resource and financial standpoint for those producers that continue to use CT systems and especially those that have recently adopted ST systems into their farming operations.     

Improved water capture and erosion reduction through furrow diking

Crop production in Georgia and the Southeastern U.S. can be limited by water; thus, supplemental irrigation is often needed to sustain profitable crop production. Increased water capture would efficiently improve water use and reduce irrigation amounts and other input costs, thus improving producer's profit margin. We quantified water capturing and erosional characteristics of furrow diking by comparing runoff (R) and soil loss (E) from furrow diked (DT) and non-furrow diked tilled (CT) systems. A field study (Faceville loamy sand, Typic Kandiudult) was established (2006 and 2007) near Dawson, GA with DT and CT systems managed to irrigated cotton (Gossypium hirsutum L.). Treatments included: DT vs. CT; DT with and without shank (+/− S); and rainfall simulation performed (0, 60 days after tillage, DAT). Simulated rainfall (50 mm h⁻¹ for 1 h) was applied to all 2 m × 3 m plots (n = 3). All runoff and E were measured from each flat, level sloping 6-m² plot (slope = 1%). Compared to CT, DT decreased R and E by 14-28% and 2.0-2.8 times, respectively. Compared to DT − S, DT + S decreased R and E by 17-56% and 26% to 2.1 times, respectively. Compared to sealed/crusted soil conditions at 60 DAT, simulating rainfall on a freshly tilled seedbed condition (DAT = 0) decreased R by 69% to 3.4 times and increased E by 27%. DT0 + S + RF0 plots (best-case scenario) had 2.8 times less R, and 2.6 times less E than CT − S + RF60 plots (worst-case). Based on $1.17 ha-mm⁻¹ to pump irrigation water and $18.50 ha⁻¹ for DT, a producer in the Coastal Plain region of Georgia would recover cost of DT by saving the first 16 ha-mm of water. The DT + S system is a cost-effective management practice for producers in Georgia and the Southeastern U.S. that positively impacts natural resource conservation, producer profit margins, and environmental quality.     

Controlling runoff under low pressure center pivot irrigation systems

A research study was conducted in commercial potato production fields irrigated by low pressure center pivot irrigation systems for three growing seasons in southern Idaho, USA. Plots were established to give several replications of both conventional and reservoir tillage under the outermost spans, where the highest application rates occur. The soil was silt loam, and the topography varied from nearly level to 5% slopes. The sprinkler devices included spray nozzles on drops (spraydrops), spray nozzles on booms (spraybooms) and rotator spray nozzles on drops (rotator spraydrops) with an operating pressure of 138 kPa.The purpose of this study was to investigate and assess the role of reservoir tillage on controlling runoff, uniformity of soil water content throughout the field, and crop yield, as compared with conventional tillage. Reservoir tillage effectively reduced runoff losses to less than 1% of the applied water, when the dike were intact and remained stable. Over the three years of this study reservoir tillage increased the average soil water content by 18%. In addition, a statistical analysis showed that reservoir tillage significantly increased the percent available water in the top 65 cm of the root zone (P=0.01). The use of reservoir tillage elevated average yield by 21%, and average percent number one tubers was increased from 64% for conventional plots to 68% for reservoirtilled plots. While reservoir tillage increased the yield significantly (P=0.01), the sprinkler type did not have a significant influence on yield.     

Effects of winter wheat row spacing on evapotranpsiration, grain yield and water use efficiency

A field study was conducted from 2002 to 2007 to investigate the influence of row spacing of winter wheat (Triticum aestivum L.) on soil evaporation (E), evapotranspiration (ET), grain production and water use efficiency (WUE) in the North China Plain. The experiment had four row spacing treatments, 7.5 cm, 15 cm, 22.5 cm, and 30 cm, with plots randomly arranged in four replicates. Soil E was measured by micro-lysimeters in three seasons and ET was calculated from measurements of soil profile water depletion, irrigation, and rainfall. The results showed that E increased with row spacing. Compared with the 30-cm row spacing (average E = 112 mm), the reduction in seasonal E averaged 9 mm, 25 mm, and 26 mm for 22.5 cm, 15 cm, and 7.5 cm row spacings, respectively. Crop transpiration (T) increased as row spacing decreased. The seasonal rainfall interception and seasonal ET were relatively unchanged among the treatments. In three out of five seasons, the four different treatments showed similar grain yield, yield components and WUE. We conclude that for winter wheat production in the North China Plain, narrow row spacing reduced soil evaporation, but had minor improvements on grain production and WUE under irrigated conditions with adequate nutrient levels.     

Effects of conservation tillage practices on winter wheat water-use efficiency and crop yield on the Loess Plateau,China

In the semi-humid to arid loess plateau areas of North China, water is the limiting factor for rain-fed crop yields. Conservation tillage has been proposed to improve soil and water conservation in these areas. From 1999 to 2005, we conducted a field experiment on winter wheat (Triticum aestivum L.) to investigate the effects of conservation tillage on soil water conservation, crop yield, and water-use efficiency. The field experiment was conducted using reduced tillage (RT), no tillage with mulching (NT), subsoil tillage with mulching (ST), and conventional tillage (CT). NT and ST improved water conversation, with the average soil water storage in 0–200 cm soil depth over the six years increased 25.24 mm at the end of summer fallow periods, whereas RT soil water storage decreased 12 mm, compared to CT. At wheat planting times, the available soil water on NT and ST plots was significantly higher than those using CT and RT. The winter wheat yields were also significantly affected by the tillage methods. The average winter wheat yields over 6 years on NT or ST plots were significantly higher than that in CT or RT plots. CT and RT yields did not vary significantly between them. In each study year, NT and ST water-use efficiency (WUE) was higher than that of CT and RT. In the dry growing seasons of 1999–2000, 2004–2005 and the low-rainfall fallow season of 2002, the WUE of NT and ST was significantly higher than that of CT and RT, but did not vary significantly in the other years. For all years, CT and RT showed no WUE advantage. In relation to CT, the economic benefit of RT, NT, and ST increased 62, 1754, and 1467 yuan ha⁻¹, respectively, and the output/input ratio of conservation tillage was higher than that of CT. The overall results showed that NT and ST are the optimum tillage systems for increasing water storage and wheat yields, enhancing WUE and saving energy on the Loess Plateau.     

Annual carbon and nitrogen loadings for a furrow-irrigated field

Evaluations of agricultural management practices for soil C sequestration have largely focused on practices, such as reduced tillage or compost/manure applications, that minimize soil respiration and/or maximize C input, thereby enhancing soil C stabilization. Other management practices that impact carbon cycling in agricultural systems, such as irrigation, are much less understood. As part of a larger C sequestration project that focused on potential of C sequestration for standard and minimum tillage systems of irrigated crops, the effects of furrow irrigation on the field C and N loading were evaluated. Experiments were conducted on a laser-leveled 30 ha grower's field in the Sacramento valley near Winters, CA. For the 2005 calendar year, water inflow and runoff was measured for all rainfall and irrigation events. Samples were analyzed for C and N associated with both sediment and dissolved fractions. Total C and N loads in the sediment were always higher in the incoming irrigation water than field runoff. Winter storms moved little sediment, but removed substantial amounts of dissolved organic carbon (DOC), or about one-third of the total C balance. Despite high DOC loads in runoff, the large volumes of applied irrigation water with sediment and DOC resulted in a net increase in total C for most irrigation events. The combined net C input and N loss to the field, as computed from the field water balance, was 30.8 kg C ha⁻¹ yr⁻¹ and 5.4 kg N ha⁻¹ yr⁻¹ for the 2005 calendar year. It is concluded that transport of C and N by irrigation and runoff water should be considered when estimating the annual C field balance and sequestration potential of irrigated agro-ecosystems.     

Tillage and irrigation effects on crop yields and soil properties under the rice-wheat system in the Indian Himalayas

Conservation tillage systems generally improve soil organic C (SOC), plant available water capacity (PAWC), aggregation and soil water transmission. A field experiment was conducted for 4 years (2001-2002 to 2004-2005) to study tillage (conventional tillage (CT) and zero tillage (ZT)) systems. The selected irrigation treatments were at four levels (I₁: pre-sowing (PS), I₂: PS + active tillering (AT)/crown root initiation (CRI), I₃: PS + AT/CRI + panicle initiation (PI)/flowering (FL), and I₄: PS + AT/CRI + PI/FL + grain filling (GF)), applied at the critical growth stages on rice (Oryza sativa L.) and wheat (Triticum aestivum L.). Their effects on direct seeded rice productivity and soil properties (SOC and selected physical properties) after rice and wheat harvest were investigated. Soil organic C contents after rice and wheat harvest in the 0-15 cm soil depth were higher under ZT than under CT. Soil organic C increased significantly with I₂ over I₁ for both crops and with I₄ over I₂ for the wheat crop. The PAWC was significantly higher with ZT than CT. Zero tilled and frequently irrigated plots showed enhanced infiltration characteristics (infiltration rate, cumulative infiltration and sorptivity) and saturated hydraulic conductivity. Both direct seeded rice and wheat yields were not significantly different in the plots under ZT and CT. There was a significant increase in both rice and wheat yields in the plots under I₂ over I₁. However, water use efficiency between irrigation treatments was not significantly different. Hence, under direct seeded rice-wheat system in a sandy clay loam soil of the sub-temperate Indian Himalayas, farmers may adopt ZT with two irrigations in each crop for optimum resource conservation.     

Yield and seasonal water productivity of sunflower as affected by tillage and cropping systems under dryland conditions in the Limpopo Province of South Africa

Sustainable food production in semi-arid tropical countries can be achieved through efficient utilization of rainwater. A field experiment to assess the grain yield, seasonal water use (WU), water use efficiency (WUE) and precipitation use efficiency (PUE) of sunflower (Helianthus annuus L.) intercropped with cowpea (Vigna unguiculata L.) on two tillage systems was conducted during the 2007/2008 and 2008/2009 cropping seasons at the University of Venda (22°58′ S, 30°26′ E at 596 m above sea level). The experiment was configured as a 2 × 2 × 2 factorial design with three replications. The tillage treatments were conventional tillage (CT) (control) and in-field rainwater harvesting (IRWH) system. The IRWH is a special crop production technique that promotes runoff on 2.0-m wide no-till strip between crop rows and collects the runoff water in basins where it infiltrates into the soil profile. The treatments in the cropping system (CS) consisted of a sole crop (sunflower or cowpea) and an intercrop (sunflower × cowpea). Results of the experiment revealed that IRWH led to a significant (P < 0.05) increase in sunflower grain yield in the second season but cowpea grain yield was not influenced by tillage systems. IRWH resulted in significantly higher WU, WUE and PUE of both crops compared to CT system in the second season. The CS had significant effects on sunflower grain yield in both seasons but none on the cowpea grain yield. WU was significantly higher in intercrops than in sole cowpea and sole sunflower in the first and second season, respectively. WUE and PUE were significantly greater in sole sunflower than in the intercrops but less in the sole cowpea than in the intercrops.     

The agronomic and economic benefits of fertilizer and mulch use in highland banana systems in Uganda

Banana is the most important food crop in Uganda. However, there has been a decline in productivity, attributed to declining soil fertility, drought, pests and diseases and crop management factors. This study aimed to explore the possibility of increasing yields through the use of fertilizer and mulch, and to evaluate the benefits of these inputs across the major banana producing regions in Uganda. This study was carried out in 179 smallholder plots in Central, South, Southwest and East Uganda in 2006/7. Half of the plots were ‘demonstration plots’ of an agricultural development project, while the other half were neighboring farmer plots that acted as ‘control’. Demonstration plots received mineral fertilizer (100% of plots), averaging 71 N, 8 P, 32 K kg ha⁻¹ yr⁻¹ and external mulch from grass and crop residues (64% of plots), whereas control plots received no mineral fertilizer and little external mulch (26% of plots). Demonstration plots had significantly (P ? 0.05) higher yields than control plot in Central, South and Southwest, but average yield increases varied from 4.8 t ha⁻¹ yr⁻¹ (Southwest) to 8.0 (Central), and 10.0 (South). Average weevil corm damage (3%) and nematode-induced root necrosis (7%) was low and similar for both plot types, so yield increases could only be explained by the use of fertilizer and mulch. The highest demonstration plot yield increases were observed where fertilizer addressed key nutrient deficiencies identified using the compositional nutrient diagnosis approach. Farm gate bunch prices declined from 0.17 (Central Uganda) to 0.07 USD kg⁻¹ (Southwest Uganda). Consequently, average marginal rate of return (MRR) of fertilizer and mulch use ranged from 0.1 (Southwest) to 5.8 (Central). The technologies were likely to be acceptable to farmers (MRR ? 1.00) up to 160 km away from the capital. Fertilizer use is likely to be acceptable in all regions (MRR = 0.7-9.4) if local fertilizer prices of 2006/7 (average USD 0.56 kg⁻¹ of fertilizer) declined by 50%. Doubling of fertilizer prices is likely to make fertilizer use unacceptable beyond 100 km away from the capital. The study concludes that there is scope for increased input use in banana systems in Uganda, but that regional variations in crop response, input/output prices, and price fluctuations have to be taken into account.     

Opportunities for yield increases and environmental benefits through site-specific nutrient management in rice systems of Zhejiang province,China

Environmental pollution by nitrogen (N) leaching or runoff from rice fields and high pesticide use has become a serious concern in China. Average N application is high and fertilizer-N use efficiency is low compared with other major rice growing countries. In Zhejiang, rice farmers apply 150–250 kg ha⁻¹ fertilizer N and 7–10 sprays of pesticides per season to maintain yield levels of 5.5–8.0 t ha⁻¹. Fertilizer and pest management strategies of farmers are not based on plant nutrient demand and pest control requirements. To provide farmers with options for high yielding, yet more resourceful management options, site-specific nutrient management (SSNM) was developed at Zhejiang University in collaboration with the International Rice Research Institute (IRRI). The approach comprises guidelines that allow farmers to adjust domain- and season-specific fertilizer recommendations to actual growing conditions in their fields taking into account plant nutrient demand, indigenous nutrient supply, nutrient use efficiency, as well as socio-economic factors. The main objective of this paper is to evaluate the agronomic performance of SSNM in farmers’ fields in the past seven years (1998–2004). With SSNM, average grain yield increased by about 0.5 t ha⁻¹ over the farmers’ practice, while N use efficiency increased significantly. About 30% of both fertilizer N could be reduced through adoption of SSNM, which would effectively eliminate an unnecessary source of pollution in the rice ecosystem. Larger scale dissemination of SSNM for rice is under way in Zhejiang province, but stronger institutional support is urgently required.     

Runoff estimation in southern Brazil based on Smith's modified model and the Curve Number method

The objective of this work was to measure and model the runoff for different soils classes at different rainfall intensities (30, 60 and 120 mm h⁻¹) in Southern Brazil. A portable rainfall simulator with multiple nozzles was used to simulate these rainfall intensities. For each soil, the initial time and runoff rate, rainfall characteristics (total, duration and intensities), surface slope, crop residue amount and cover percentage, soil densities (bulk and particle), soil porosity (bulk, macro and micro), textural fractions (clay, silt and sand), and the initial and saturated soil water content were measured. The runoff measured was compared to Smith's modified and Curve Number (USDA-SCS) models. The cumulative runoff losses were 67, 45 and 27% of the total rainfall, for a Rhodic Paleudalf, Typic Quartzipsamment and Rhodic Hapludox, respectively. An inverse relationship was observed between initial runoff and the runoff rate, independently of the soil surface and rainfall conditions. Increasing rainfall intensity decreased the time to runoff and increased runoff rate. The Smith's modified model overestimated the cumulative runoff by about 4%. The Smith's modified model presented a better estimate for both higher and lower rainfall intensities (120 and 30 mm h⁻¹). The SCS Curve Number model overestimated the cumulative runoff by about 34%. This large overestimate is probably due to that the model did not take into account the soil tillage system used in the field by farmers, particularly for irrigated conditions. The combination of high porosity, low bulk density and presence of crop residue on soil surface decreased runoff losses, independently of the soil texture class. Smith's modified model better estimated the surface runoff for soil with a high soil water content, and it was considered satisfactory for Southern Brazil runoff estimations. The SCS Curve Number model overestimated the cumulative runoff and its use needs adjustments particularly for no-tillage management system.     

Micro-catchment water harvesting potential of an arid environment

Micro-catchment water harvesting (MCWH) requires development of small structures across mild land slopes, which capture overland flow and store it in soil profile for subsequent plant uses. Water availability to plants depends on the micro-catchment runoff yield and water storage capacity of both the plant basin and the soil profile in the plant root zone. This study assessed the MCWH potential of a Mediterranean arid environment by using runoff micro-catchment and soil water balance approaches. Average annual rainfall and evapotranspiration of the studied environment were estimated as 111 and 1671 mm, respectively. This environment hardly supports vegetation without supplementary water. During the study period, the annual rain was 158 mm in year 2004/2005, 45 mm in year 2005/2006 and 127 mm in year 2006/2007. About 5000 MCWH basins were developed for shrub raising on a land slope between 2 and 5% by using three different techniques. Runoff at the outlets of 26 micro-catchments with catchment areas between 13 and 50 m² was measured. Also the runoff was indirectly assessed for another 40 micro-catchments by using soil water balance in the micro-catchments and the plant basins. Results show that runoff yield varied between 5 and 187 m³ ha⁻¹ for various rainfall events. It was between 5 and 85% of the incidental rainfall with an average value of 30%. The rainfall threshold for runoff generation was estimated about 4 mm. Overall; the soil water balance approach predicted 38-57% less water than micro-catchment runoff approach. This difference was due to the reason that the micro-catchment runoff approach accounted for entire event runoff in the tanks; thus showed a maximum water harvesting potential of the micro-catchments. Soil water balance approach estimated water storage in soil profile and did not incorporate water losses through spillage from plant basins and deep percolation. Therefore, this method depicted water storage capacity of the plant basins and the root zone soil profile. The different between maximum water harvesting potential and soil-water storage capacity is surplus runoff that can be better utilized through appropriate MCWH planning.     

Evaluation of post-rainy season crops with residual soil moisture and different tillage methods in rice fallow of eastern India

In eastern India, farmers grow rice during rainy season (June-September) and land remains fallow after rice harvest in the post-rainy season (November-May) due to lack of sufficient rainfall or irrigation facilities. But in lowland areas of eastern India, sufficient carry-over residual soil moistures are available in rice fallow in the post-rainy season (November-March), which can be utilized for growing second crops in the region. During the post-rainy season when irrigation facilities are not available and rainfall is meager, effective utilization of carry-over residual soil moisture and conservation agriculture become imperative for second crop production after rice. Implementation of suitable tillage/seeding methods and other agro-techniques are thus very much important to achieve this objective. In this study four pulse crops (lathyrus, blackgram, pea, and greengram) were sown utilizing carry-over residual soil moisture and with different tillage/seeding methods viz. relay cropping (RC)/farmers’ practice, reduced tillage (only two ploughing) (RT), conventional tillage (CT) and zero tillage (ZT). Study revealed that the highest grain yields of 580, 630, 605 and 525 kg ha⁻¹ were obtained from lathyrus, blackgram, pea and green gram, respectively, with RT treatment. On the other hand, with conventional tillage, 34-44% lower yields were obtained than that of RT. Crops with reduced tillage performed better than that with zero tillage or relay cropping also. Impacts of different tillage methods on important soil physical properties like infiltration, bulk density were also studied after harvesting first crop (rice) and before growing second crops (pulses) in rice fallow. The lowest mean bulk density (1.42) was recorded in the surface soils of CT treatment while the corresponding value under ZT treatment was 1.54 Mg m⁻³.     

Simulation of nitrate-N movement in southern Ontario,Canada with DRAINMOD-N

DRAINMOD-N, a mathematical model to predict nitrate-N concentrations in surface runoff and drain outflows from subsurface-drained farmlands, has been tested against field data collected in southern Ontario. The data was collected in a corn field from 16 conventional drainage and subirrigation plots in Woodslee, Ontario, from 1992 to 1994. The model performance was evaluated by comparing the observed and simulated nitrate-N concentrations in surface runoff and drain outflows. A precise calculation of water-table depth is an essential prerequisite for a model to obtain a proper prediction of nitrate-N movement. For the simulation of water-table depth, the lowest root mean square error and the highest correlation coefficient of linear regression were 173 mm and 0.51 for the subirrigation plots; and 178 mm and 0.84 for the subsurface drainage plots. Therefore, the performance of DRAINMOD-N for soil hydrologic simulations was satisfactory and it could be used for assessing nitrogen fate and transport. For the simulation of nitrate-N losses in the subirrigation plots, the lowest root mean square error and the highest correlation coefficient of linear regression were 0.74 kg/ha and 0.98 for surface runoff; and 6.53 kg/ha and 0.91 for drain outflow. For the simulation in the subsurface drainage plots, the lowest root mean square error and the highest correlation coefficient of linear regression were 0.70 kg/ha and 0.96 for surface runoff; and 6.91 kg/ha and 0.92 for drain outflow. The results show that DRAINMOD-N can perform satisfactory simulation of soil hydrology and nitrate-N losses in surface runoff under various water-table management practices. The model can, therefore, be used to evaluate different water pollution scenarios and help in the development and testing of various pollution control strategies for fields in cold weather such as that in southern Canada.     

The effect of system innovations on water productivity in subsistence rainfed agricultural systems in semi-arid Tanzania

Rainfed subsistence farming systems in sub-Saharan Africa generally obtain low crop yields as a result of highly erratic rainfall seasons. This paper presents results of research conducted to test the effects of improvements in farming techniques for subsistence rainfed systems. The research was carried out in the Makanya catchment of northern Tanzania where rainfall of less than 600 mm a⁻¹ and spread over two agricultural seasons per year is clearly insufficient to support staple food crops under the present farming systems in the area. The research sought to prove that, with improved efficiency in tillage techniques, grain yields can improve even under the existing challenging hydro-climatic conditions. The research tested farming system innovations (SIs) at four sites located within a spatial distance of 10 km where a combination of runoff diversion (RD), on-site rain water harvesting (WH) and conservation tillage (CT) were compared against the traditional farming methods of hand-hoeing under strict rainfed conditions (Control). For RD, runoff generated from natural storms was directed into infiltration pits dug along the contour with the excavated soil deposited upward of the trenches (fanya juus). The impact of these techniques on maize yields under different SIs was investigated.The results showed that the innovations resulted in increased maize grain yields of up to 4.8 t ha⁻¹ compared against current averages of less than 1 t ha⁻¹. The average productivity of the available water over four seasons was calculated to range between 0.35 and 0.51 kg m⁻³. For the SIs that were tested, the distribution of yields within a cultivated strip showed variations with better yields obtained on the down slope side of the cultivated strip where ponding effects resulted in higher water availability for infiltration and storage. However, due to the large seasonal climate variability, statistical analysis did not show significant differences in the yields (p < 0.05) between different cultivation techniques.The study showed that there is scope to improve grain yields with the little available rainfall through the adoption of techniques which promote water availability and retention within the field. The re-partitioning of water within the field creates mitigation measures against the impact of dry spells and allows alternative cropping in addition to the traditional maize cultivated in the rainfall seasons.     

Response of cotton to various levels of nitrogen and water applied to normal and paired sown cotton under drip irrigation in relation to check-basin

Field experiments were conducted for 2 years to investigate the effects of various levels of nitrogen (N) and methods of cotton planting on yield, agronomic efficiency of N (AEN) and water use efficiency (WUE) in cotton irrigated through surface drip irrigation at Bathinda situated in semi-arid region of northwest India. Three levels of N (100, 75 and 50% of recommended N, 75 kg ha⁻¹) were tested under drip irrigation in comparison to 75 kg of N ha⁻¹ in check-basin. The three methods of planting tried were; normal sowing of cotton with row to row spacing of 67.5 cm (NS), normal paired row sowing with row to row spacing of 35 and 100 cm alternately (NP) and dense paired row sowing with row to row spacing of 35 and 55 cm alternately resulting in total number rows and plants to be 1.5 times (DP) than NS and NP. In NS there was one lateral along each row, but in paired sowings there was one lateral between each pair of rows. Consequently the number of laterals and quantity of water applied was 50 and 75% in NP and DP, respectively, as compared with NS in which irrigation water applied was equivalent to check-basin.Drip irrigation under NS resulted in an increase of 258 and 453 kg ha⁻¹ seed cotton yield than check-basin during first and second year, respectively, when same quantity of water and N was applied. Drip irrigation under dense paired sowing (DP) in which the quantity of irrigation water applied was 75% as compared with NS, further increased the yield by 84 and 101 kg ha⁻¹ than NS during first and second year, respectively. Drip irrigation under NP, in which the quantity of water applied and number of laterals used were 50% as compared with drip under NS, resulted in a reduction in seed cotton yield of 257 and 112 kg ha⁻¹ than NS during first and second year, respectively. However, the yield obtained in NP under drip irrigation was equivalent to yield obtained in NS under check-basin during first year but 341 kg ha⁻¹ higher yield was obtained during second year. The decrease in N applied, irrespective of methods of planting, caused a significant decline in seed cotton yield during both the years. Water use efficiency (WUE) under drip irrigation increased from 1.648 to 1.847 and from 0.983 to 1.615 kg ha⁻¹ mm⁻¹ during first and second year, respectively, when the same quantity of N and water was applied. The WUE further increased to 2.125 and 1.788 kg ha⁻¹ mm⁻¹ under DP during first and second year, respectively. The agronomic efficiency of nitrogen was higher in drip than check-basin during both the years when equal N was applied. The WUE decreased with decrease in the rate of N applied under fertigation but reverse was true for AEN. It is evident that DP under drip irrigation resulted in higher seed cotton yield, WUE and AEN than NS and also saved 25% irrigation water as well as cost of laterals.     

Polyacrylamide coated Milorganite™ and gypsum for controlling sediment and phosphorus loads

The application of polymer for controlling erosion and the associated nutrient transport has been well documented. However, comparatively less information is available on the effect of polymer application together with soil amendments. In this study, the effect of polyacrylamide (PAM) in combination with surface application of gypsum and Milorganite™ (MILwaukee ORGAnic NITtrogEn) biosolid for reducing sediment and phosphorus transport under laboratory rainfall simulations was investigated. The treatments considered were bare soil, gypsum, Milorganite™, gypsum + Milorganite™, PAM-coated gypsum and PAM-coated Milorganite™. Application rates for gypsum and Milorganite™ were 392 kg ha⁻¹ (350 lb/acre) and 726 kg ha⁻¹ (650 lb/acre), respectively. The PAM was coated on gypsum and Milorganite™ at an application rate of 11.2 kg ha⁻¹ (10 lb/acre) and 22.4 kg ha⁻¹ (20 lb/acre), respectively. Rain simulation experiments were conducted using a rainfall intensity of 6.0 cm h⁻¹ for 1 h on a 10% slope. Surface runoff was collected continuously from each soil box over 10 min intervals and leachate was collected continuously over the 60 min simulation. The reduction in runoff or in leachate for all treatments was not significantly different from the bare soil control. The sediment loss for PAM coated Milorganite™ was reduced by 77%, when compared to bare soil. However, the sediment loss was not significantly reduced for any other treatment compared to bare soil. The PAM-coated gypsum was not effective for erosion control in our study, and there appears to be a correlation between effectiveness and prill size. However, the gypsum (coated and uncoated) contributed about half of the dissolved reactive phosphorus (DRP) export (in the runoff) compared to bare soil. The PAM-coated Milorgante™ reduced the DRP and total phosphorus (TP) export to 0.3-0.5 times that of Milorganite™ and to levels similar to bare soil. The decreased sediment and phosphorus export for the PAM-coated Milorganite™ treatment is a signal for a potential management practice for controlling erosion and nutrient transport in fertilized agricultural landscapes.