Johannes Scholberg

Soil Moisture Controlled Subsurface Drip Irrigation on Sandy Soils

Subsurface drip irrigation (SDI) is being adopted in areas to conserve water while maintaining economical production of crops. These systems have not been evaluated on sandy soils common to Florida. An SDI system was installed on a well-drained sandy soil for sweet corn production in Florida. SDI tubing was buried under each row (76-cm spacing) at either two depths of 23 or 33 cm below the ground surface to result in two experimental treatments. Additionally, two methods of irrigation scheduling were imposed on the SDI treatments. One scheduling treatment was the initiation and termination of irrigation based on soil moisture measured by time domain reflectometry (TDR) probes installed 5 cm above the drip line. The other scheduling treatment was a daily irrigation event at rates consistent with typical practice in the region. Sprinkler irrigation scheduled similar to farmer practices in the region and non-irrigated control treatments were also established. The soil moisture based irrigation scheduling regime resulted in high frequency short duration (30-min) irrigation events to meet crop water needs. The 23-cm deep soil moisture-based treatment resulted in similar yields and similar water use in 2002 and reduced water use 11% with similar yields compared to sprinkler irrigation in 2003. This indicates that 23-cm deep SDI is feasible for sweet corn production under these conditions. The combination of optimum yield and minimum water use was achieved with soil moisture based set points of 10% to 12% by volume (on-off). The 33-cm depth SDI treatment was found to be too deep for optimal yield results on sweet corn under the type of sandy soil in the study. Time-based SDI treatments were under-irrigated but showed evidence of considerable drainage based on soil moisture measurements due to single daily irrigation events that promoted movement of irrigation water below the root zone. Comparison of drainage calculations beneath the SDI treatments and sprinkler treatments indicated that up to 24% less drainage may have occurred on SDI plots compared to sprinkler plots largely because SDI applied water to the root zone and not the furrows.

Irrigation Scheduling for Green Bell Peppers Using Capacitance Soil Moisture Sensors

Vegetable production areas are intensively managed with high inputs of fertilizer and irrigation. The objectives of this study were to evaluate the interaction between N-fertilizer rates and irrigation scheduling using soil moisture sensor irrigation controllers (SMS) on yield, irrigation water use efficiency (IWUE) of bell pepper cultivated under plastic mulch and drip irrigation. Treatments included three irrigation scheduling and three N-rates (176, 220, and 330 kg/ha). Irrigation treatments were: SS10 , water application controlled by SMS-based irrigation set at 10% volumetric water content (VWC) which was allotted five irrigation windows daily and bypassed events if the soil VWC exceeded the established threshold; SS12 , threshold set at 12% VWC; and TIME, control with irrigation being applied once a day similar to grower irrigation management. Marketable yields ranged between 16 and 29 Mg/ha. The SMS treatments reduced the applied irrigation in 7 to 62% compared to TIME treatment without reducing yi...

Adaptation of the CROPGRO model to simulate the growth of field-grown tomato

Modelling the growth of field-grown tomato (Lycopersicon esculentum Mill.) should assist growers and extension workers throughout the world to outline optimal crop management strategies for specific locations and production systems. In previous use of a greenhouse tomato model (TOMGRO), effects of nutrient and water stress on the growth of field-grown tomato were not accounted for, and it was decided to modify a more generic growth model (CROPGRO) that does address these issues. It proved feasible to capture growth and production features typical of field-grown tomato by modifying existing parameter files previously used for peanut (Arachis hypogaea L.), without changing the FORTRAN code or model structtire. Parameter estimation and model calibration involved use of data sets for three seasons of field-grown tomato at the Gulf Coast Research and Education Centre (GCREC) in Bradenton, Florida, USA. Photosynthetic parameters were calculated by comparison to the TOMGRO model. Some of the more important parameter modifications, and their implications with respect to modelling results, are presented. Results from these initial modifications using the CROPGRO generic crop model show both the versatility and the robustness of the model. The general procedure presented here may also be employed as a ‘blueprint’ for future CROPGRO adaptation to other vegetable crops.

Fertilizer residence time affects nitrogen uptake efficiency and growth of sweet corn

Understanding plant N uptake dynamics is critical for increasing fertilizer N uptake efficiency (FUE) and minimize the risk of N leaching. The objective of this research was to determine the effect of residence time of N fertilizer on N uptake and FUE of sweet corn. Plants were grown in 25 L columns during the fall and spring to mimic short-term N uptake dynamics. Nitrogen was applied either 1, 3, or 7 d before a weekly leaching event, using KNO3 solution (total of 393 kg N ha(-1)). Residence times (tR) were tR-1, tR-3, and tR-7 d before weekly removal of residual soil N. Plant N uptake was calculated by comparing weekly N recovery from planted with non-planted columns. During the fall, N uptake values at 70 d after emergence were 59, 73, and 126 kg N ha(-1). During the spring, corresponding values were 54, 108, and 159 kg N ha(-1). A linear response of plant growth and yield to the tR was observed under cooler conditions, whereas a quadratic response occurred under warmer conditions. There was correlation between root length density and yield. It is concluded that increasing N fertilizer residence time, which is indicative of better irrigation practices, enhanced overall sweet corn growth, yield, N uptake, and FUE, consequently reduced the risk of N being leached below the root zone before complete N uptake.

Effects of green manure use on sweet corn root length density under reduced tillage conditions

A green manure (GM) is a crop grown primarily as a nutrient source and soil amendment for subsequent crops. In environments such as Florida, combined use of GM and reduced tillage may improve soil water and nutrient retention and reduce potential groundwater pollution. In the first 3 years of a long-term experiment, use of GM in a reduced-tillage system on a sandy Florida soil benefited the season-long growth of sweet corn ( Zea mays L. var. Rugosa) much more than final ear yields. To help understand these patterns, we evaluated response of sweet corn roots when in rotation with GM of sunn hemp ( Crotalaria juncea L.; summer) and cahaba white vetch ( Vicia sativa L.; winter 2002–2003) and a multi-species mixture of hairy vetch ( V. villosa Roth.) and cereal rye ( Secale cereale L.; winter 2003–2004). Treatments included sweet corn with combinations of 0 or 133 kg chemical N ha −1 (as NH 4 NO 3 ) and with or without GM. A highly fertilized treatment (267 kg chemical N ha −1 ) without GM was also included. Soil cores were sampled from three depths (0–15, 15–30 and 30–60 cm) both between and within corn rows. Data from two experiments showed that use of GM increased sampled corn root length density (RLD) by 44–54%, although only within the upper 15 cm of soil in one of the two experiments. Corn following GM plus 133 kg chemical N ha −1 produced up to 44% greater RLD than corn with 267 kg chemical N ha −1 . Sampled RLD decreased with distance away from corn plants (from in-row to between-row positions, and from shallow to deeper depth), with roughly 85–95% of sampled RLD existing in the top 30 cm of soil across all treatments. During the 2004 experiment, we found that broadcast, as opposed to banded (placed along corn row only), chemical N application resulted in more even distribution of corn RLD between in-row and between-row positions during late-season without regard to GM crop. Although GM permitted optimal sweet corn growth with a 50% reduction in chemical N application, ear fill during the final 1–2 weeks before harvest may have been reduced in GM treatments. GM effects on the amount and spatial distribution of sweet corn RLD may help explain these trends. Provision of greater N from GM residues and/or altered distribution of supplementary chemical N and irrigation may be required to achieve greater ear yield benefit from GM.

Weed suppression with hydramulch, a biodegradable liquid paper mulch in development

Cost-effective, laborsaving, and environmentally sound weed management practices are needed for sustainable vegetable production. Organic production, in particular, precludes the use of synthetic herbicides and requires that organic farmers utilize practices that reduce harmful environmental impact. Although polyethylene film mulch is used extensively in vegetable production in Florida, its use has a number of drawbacks, among which is the susceptibility of opaque polyethylene mulch to penetration by yellow and purple nutsedge. Appreciable labor and disposal/environmental costs are associated with its removal. A durable mulch material that would effectively control nutsedge and other weeds but with no associated environmental and disposal costs is highly desirable. Hydramulch, a paper-like material applied as a slurry consisting of cotton waste, newsprint, gypsum and a proprietary adhesive, was tested as a biodegradable alternative to polyethylene mulch during the spring of 2003. Experiments were conducted in southeastern and north-central Florida to compare the effects of three hydramulch formulations, polyethylene mulch and a no mulch control on soil temperature, soil moisture and weed infestation. Soil temperature under hydramulch was 1‐4C lower than that under polyethylene. In the absence of rain, the use of hydramulch resulted in soil moisture levels that were 1‐4% lower than with polyethylene mulch. Higher soil moisture with hydramulch than polyethylene was coincident with rainfall. Hydramulch remained intact on most beds and suppressed broadleaf weeds and grasses, particularly at the north-central site where the mulch was applied at a greater thickness. However, purple nutsedge readily penetrated hydramulch. Therefore, hydramulch may be applicable for use for the suppression of broadleaf weeds and grasses at sites with little or no nutsedge pressure in fall or in crops for which cooler soils are desirable or crops that are rainfed or overhead irrigated.

Enhancing fertilizer efficiency in high input cropping systems in Florida

During the last century, a number of strategies have been used to determine optimal N-fertilizer rates and to develop appropriate N-fertilizer recommendations for intensively-managed cropping systems. However, these strategies lack a system-based approach and the precision needed to warrant high yields while addressing environmental concerns in a cost-effective manner. Therefore, a more holistic approach is required to enhance fertilizer use efficiency (FUE) in high input agricultural systems that pose both large environmental and economic risks. This article presents a physiological basis for improving FUE in these systems by linking physiological crop nutrient requirements with nutrient uptake efficiencies as affected by root characteristics, crop N demand, and production management practices. Starting at the crop and field level we outline key processes affecting crop N demand and uptake efficiency. For this purpose we reviewed key scientific papers that describe yield response and fertilizer uptake efficiencies with special reference to pepper (Capsicum annuum L.), potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum L.) crops in Florida production systems. This because such systems are especially prone to N leaching. Based on this review it is evident that yield response to fertilizer for most crops tend to be inconsistent both within and across locations. Therefore, use of standard recommendations may not be appropriate since they pose substantial economic and environmental risks.

Automated Subsurface Drip Irrigation Based on Soil Moisture

A subsurface drip irrigation (SDI) system was installed on a well-drained sandy soil for sweet corn and peanut production in Florida. SDI tubing was buried under each row (76 cm spacing) at either two depths of 23 or 33 cm below the ground surface to result in two experimental treatments. Additionally, two methods of irrigation scheduling were imposed on the SDI treatments. One scheduling treatment was the initiation and termination of irrigation based on soil moisture measured by time domain reflectometry (TDR) probes installed 5 cm above the drip line. The other scheduling treatment was a daily irrigation event at rates consistent with typical practice in the region. Sprinkler irrigation scheduled similar to farmer practices in the region and non-irrigated control treatments were also established. The soil moisture-based irrigation scheduling regime resulted in high frequency short duration irrigation events to meet crop water needs. The 23 cm deep soil moisture based treatment resulted in similar yields and similar water use in 2002 and reduced water use 11% (23% when adjusted for excessive irrigation due to equipment problems) with similar yields compared sprinkler irrigation in 2003. The soil moisture based set points for these results were 10-12% by volume (on-off). The 33 cm depth SDI treatment was found to be too deep for optimal yield results on sweet corn under the type of sandy soil in the study. Time based SDI treatments were under-irrigated, but showed evidence of considerable drainage based on soil moisture measurements. Comparison of drainage calculations beneath the SDI treatments and sprinkler treatments indicated that up to 24% less drainage (50% for adjusted data) may have occurred on SDI plots compared to sprinkler plots. Irrigation was not necessary for peanut planted in rotation with sweet corn in the rainy Florida summer climate.

Cover Crops in Agrosystems: Innovations and Applications

Cover crops can reduce the dependence of farmers on agrochemicals while enhancing overall agrosystem’s performance. However, the inherent complexity of cover-crop-based systems hampers their adoption by conventional farmers. Therefore, special management skills and alternative research and technology transfer approaches may be required to facilitate their adoptive use by conventional farmers. We propose that development and adoption of suitable cover-crop-based production systems may require the use of an “innovation framework” that includes (1) identification of system constraints, (2) analysis of system behavior, (3) exploration of alternative systems, and (4) system design and selection. We describe case studies from four regions of the Americas (Florida, USA; Parana and Santa Catarina, Brazil; and Canelones, Uruguay) that illustrate the relationships between this innovation framework and the development and adoption of cover-crop-based production systems. Where successful, development and adoption of such systems appear to relate to a number of attributes including (1) active involvement by farmers in research and dissemination programs; (2) integration of cover crops into production systems without net loss of land or labor resources; (3) informing farmers of the (direct) benefits of cover crop use; (4) provision of multiple benefits by cover crops, (5) sufficient access to information, inputs, and technologies required for cover crop use; and (6) provision of skills and experience necessary to manage cover crops effectively. Where these attributes are absent and failure to innovate has prevented development and adoption of cover-crop-based systems, policy initiatives to reward farmers for ecological services provided by cover crops may be required.

Nitrogen Uptake Efficiency and Growth of Bell Pepper in Relation to Time of Exposure to Fertilizer Solution

Irrigation of high‐value vegetable crops on sandy soils with poor water‐retention capacities may result in fertilizer nitrogen (N) displacement below the effective root zone prior to complete crop uptake. As a result, fertilizer N‐uptake efficiency (FUE) of vegetable crops is often relatively low, thereby increasing the potential risk of groundwater contamination. The objective of this study was to determine how time of exposure of the root zone to the N fertilizer (which is referred to as “fertilizer residence time” or t R), as related to irrigation management, affects N uptake, FUE, growth, and yield of bell pepper (Capsicum annuum L.). Plants were grown in PVC columns with 45 kg of soil equipped with a drainage valve in the bottom of the column. Weekly irrigation with dissolved fertilizers (potassium nitrate; KNO3) was applied 1, 3, or 7 d before weekly removal of residual soil N by leaching. Weekly N uptake rates were calculated by comparing total N recovery between unplanted (reference) and planted columns. At 77 d after planting, increasing the t R from 1 to 3 or 7 d increased the weekly N uptake from 1.4 to 10.8 and/or 13.3 kg N ha−1, respectively. Total calculated plant N accumulations were 19, 72, and 106 kg N ha−1 for the 1‐, 3‐, and 7‐d t R treatments, with overall FUE values being 8, 31, and 45%, respectively. It is concluded that during initial growth crop, uptake capacity is limiting, and more frequent (daily) fertilizer injection into the irrigation water may be required to enhance FUE. It is proposed also that via sound or innovative irrigation management practices, fertilizer retention in the root zone can be enhanced, thereby improving crop growth, yield, and FUE while reducing production cost and potential environmental impacts.