Mulch Biomass Research Articles

A Comparison of Reduced Tillage Implements for Organic Wheat Production in Western Canada

Low‐tillage systems are needed to improve soil conservation in organic farming. This study evaluated three no‐till/low‐till cover crop termination strategies on the basis of weeds, N dynamics and growth and yield of a wheat (Triticum aestivum L.) test crop. Field experiments were conducted in two different Canadian provinces. The blade roller, flail mower, and undercutter cultivator were comparable with standard tillage for controlling a full‐season barley (Hordeum vulgare L.)–pea (Pisum sativum L.) cover crop. Reduced tillage implements resulted in some depression of soil temperature the following spring and some delay in spring wheat development. Yield differences between treatments were related to weed and N consequences not seedbed quality or wheat development. Undercutting sometimes resulted in better perennial weed control than blade rolling. Blade roll plus late‐season tillage treatment improved perennial weed control but provides less residue for soil protection. Flail mowing resulted in more rapid cover crop biomass mulch decomposition, allowing weeds to establish. Reducing tillage reduced N availability to the following wheat crop relative to tillage, and reduced N leaching. Poor weed suppression in low‐till treatments meant that a higher proportion of available N was sometimes captured by weeds compared with the wheat crop. Future studies should test combinations of alternative tillage and crop termination approaches aimed at specific weed and nutrient challenges.Core Ideas Alternative tillage tools were tested for control of cover crops preseeding spring wheat. Perennial weeds meant low tillage options were not feasible when wheat seeding was delayed. Undercutting liberated more cover crop N than blade roll but weeds sometimes captured this N.

Weed Suppression of Living Mulch in Sugar Beets

Weed suppression in sugar beets (Beta vulgaris.) is commonly achieved with two to three post-emergent herbicide applications across the entire field. Field studies were performed, in order to investigate the weed suppressing ability of Medicago lupulina, Trifolium subterraneum and a mixture of Lolium perenne and Festuca pratensis as living mulches in sugar beet at four locations in South Germany during 2014 and 2015. Living mulches were sown 2 and 30 days after sowing (DAS) of sugar beet. Weed densities ranged from 0 to 143 plants m−2 with Chenopodium album, Polygonum convolvulus and Polygonum aviculare being the most abundant weed species. It has been found that living mulches could reduce herbicide input up to 65 %. Weed suppression of living mulch was highest with Trifolium subterraneum (71 %). The early sown living mulches (2 DAS) revealed a 28 g m−2 higher biomass compared to late sowing (30 DAS). However, no any linear correlation was found between living mulch biomass and weed suppression. White sugar yield (WSY) was highest in the herbicide treatments (12.6 t ha−1). Trifolium subterraneum yielded the highest WSY of the living mulches with 11.1 t ha−1 across all locations. Our work reveals that living mulch can play a major role in integrated plant protection by reducing herbicides in sugar beet production.

Plant species and mulch application rate affected decomposition of cover crop mulches used in organic rotational no-till systems

Decomposition of cover crop mulches has received little attention in the scientific literature, particularly in the context of the organic rotational no-till systems adapted for the climatic conditions of the northern Great Plains of Canada. The objective of the study was to determine the effect of plant species and mulch application rate on cover crop decomposition and mulch quality parameters over time. Using the litter bag technique, six plant species and two mulch application rates were tested twice in field studies at Carman, Manitoba, Canada. Among the plant species tested, decomposition was the fastest with oilseed radish (Raphanus sativus L.) and the slowest with barley (Hordeum vulgare L.). The effect of application rate on mulch biomass was not consistent between experiments. Mulches released a large amount (46.4%) of their initial N content after only 30 days of field placement, for all levels of plant species and mulch application rates combined. Forty-four percent of initial N content still remained in the mulches by early May (Day 250), and may be available for the subsequent crops seeded in the spring or later in the crop rotation. This research provides us with valuable information on nutrient release, soil cover, and potential weed control from mulches.

Living mulch cover crops for weed control in small-scale applications

AbstractA primary challenge of managing vegetable production on a small land base is the maintenance and building of soil quality. Previous studies have demonstrated the benefits of cover crops for improved soil quality; however, small growers struggle to fit cover crops into rotations. Small-scale growers with limited available land are under significant pressure to maximize their saleable yield and often work to maximize output by using intensive cropping practices that may include both early and late season crops, thus limiting the typical shoulder season windows in which cover crops can be grown. In-season living mulches may be an effective strategy to provide small-scale growers the benefits of cover crops with less land commitment than cover crops used in typical rotations. However, research on living mulches is generally not suited to small-scale organic production systems due to the typical reliance on chemical herbicide to suppress mulches. An experiment was designed with the goal of evaluating living mulch systems for space-limited organic vegetable production. In a 2-year study, four living mulch crops (buckwheat (Fagopyrum esculentum), field pea (Pisum sativum), crimson clover (Trifolium incarnatum) and medium red clover (Trifolium pratense)) and a cultivated control with no mulch cover were planted in early spring each year. Snap beans (Phaseolus vulgarisvar. Tavera), transplanted bell peppers (Capsicum annuumvar. Revolution), and transplanted fall broccoli (Brassica oleraceavar. Imperial) were then planted directly into living mulches. During each summer growing season, living mulches and weeds were mown between-rows and hand-weeded in-row approximately every 10–14 days as needed for management. Labor times for mowing and cultivation were found to be higher in all treatments relative to the cultivated control. An inverse relationship between living mulch biomass and weed biomass was observed, demonstrating that living mulches may contribute to weed suppression. However, lower vegetable yields were seen in the living mulch treatments, most likely due to resource competition among vegetables, living mulches and weeds. High pre-existing weed seedbank and drought conditions likely increased competition and contributed to reduced vegetable yield.

Crop agronomic performance under a six-year continuous organic no-till system and other tilled and conventionally-managed systems in the northern Great Plains of Canada

Reducing tillage in herbicide-free cropping systems is a challenge for farmers and few studies have attempted to identify the limitations of organic no-till systems over a period of time greater than two years. The objective of the study was to determine the effect of tillage [no-till (NT) and conservation tillage (CT)] and management [organic (ORG) and conventional (CONV)] systems on mulch biomass, weeds, and crop productivity, over time. A six-year field study was conducted in Carman, MB, Canada, between 2008 and 2012. The crop rotation was barley (Hordeum vulgare L.)/hairy vetch (Vicia villosa Roth) cover crop in 2008, flax (Linum usitatissimum L.) in 2009, oats (Avena sativa L.) followed by a 4-species fall-seeded cover crop mixture in 2010, barley/hairy vetch cover crop in 2011, and spring wheat (Triticum aestivum L.) followed by fall-seeded cereal rye (Secale cereale L.) in 2012. From 2008 until mid-2010, the experiment design consisted of two tillage systems (NT and CT), both under ORG management. In mid-2010, the experiment was modified into a split-plot design to allow for the comparison between the ORG and CONV management systems, within each tillage system. In ORG NT, cash crops of flax and spring wheat were seeded into 4.5 and 4.7Mgha−1 of rolled cover crop mulch in 2009 and 2012, respectively. Differences in weed communities between treatments were statistically noticeable in the fifth year of the study only (2012), with higher weed biomass and weed species richness in the ORG management system. Crop yields were reduced in ORG NT in 2009 (flax) and 2012 (spring wheat). Little difference in weed and crop responses between ORG and CONV tilled systems were identified. Results suggest that additional innovative soil and weed management practices are needed to make organic continuous no-till cropping system productive for a period longer than six years, in a cool subhumid continental climate.

Seed yield and nutrient uptake studies on clusterbean as influenced by mulching practices, varieties and nutrient management

A field experiment was conducted at College Farm, Gwalior in M. P. during the rainy (kharif) seasons of 2013 and 2014 to study the seed yield and nutrient uptake studies on clusterbean as influenced by mulching practices, varieties and nutrient management. Results revealed that plastic mulch significantlyincreased the seed and stover yields as well as N, P and K uptake over the weed biomass mulch and no mulch. Variety HG-563 recorded significantly higher seed, stover yield, N, P and K uptake by seed, stover and total uptake as compared to RGC-1055. Among the fertility levels, application of 75% RDF+VC 5 t/ha resulted in significantly higher seed, stover yield, N, P and K uptake by seed, stover and total uptakeover all the remaining fertility levels. After harvest of crop, the available N, P and K in the soil increased in weed biomass mulch with RGC-1055 under 50% recommended dose of fertilizer+vermicompost 5 t/ha as compared to other treatments during both the years.

Flax (Linum usitatissimum L.) production system performance under organic rotational no-till and two organic tilled systems in a cool subhumid continental climate

Studies comparing crop agronomic response in organic production systems under contrasting tillage practices are lacking. The objective of the study was to compare the effect of organic rotational no-till and two organic tilled systems on the basis of mulch biomass, soil chemical properties, weed control, and subsequent crop productivity. A field study consisting of two-year sequences was conducted three times at three close sites in Carman, Manitoba, Canada (2009–2010 at site A, 2010–2011 at site B, and 2011–2012 at site C), on Chernozem soils. Three management systems of cover crops were tested, in a randomized complete block design. A barley (Hordeum vulgare L.)/hairy vetch (Vicia villosa Roth) cover crop was grown in the first year of the study and terminated by rolling (no-till), rolling and tillage (Roll+Till), or haying and tillage (Hay+Till). Flax (Linum usitatissimum L.) was seeded the following year. Our first hypothesis that a full-year growth of barley/hairy vetch cover crop allows the production of between 6 and 8Mgha−1 of mulch biomass for the subsequent crop was confirmed in two of three years. Flax was no-till seeded into 6.7, 7.7, and 4.2Mgha−1 of mulch at sites A, B, and C, respectively. At two of three sites, flax seed yields were significantly higher in no-till than in the two tillage treatments. There was no penalty on flax seed yield for haying the cover crop in mid-summer instead of incorporating it into the soil by tillage, across all three sites. There was an overall trend towards lower contents of soil nitrate-N in no-till, although it did not greatly influence total plant nitrogen uptake at two of three sites. This corroborates our second hypothesis that while flax N uptake would be reduced by the reduced soil N status in no-till, there will be sufficient N for optimum flax yield. The third hypothesis that barley/hairy vetch cover crop mulches have the ability to provide adequate weed control was generally supported, though there were important exceptions when insufficient mulch biomass was produced. Success of flax crop grown in an organic rotational no-till system in southern Manitoba depended on weather, mulch biomass production (>6.7Mgha−1), and weed species present. The fourth hypothesis that there is no yield penalty for eliminating tillage for 1.5 years in an organic flax crop in southern Manitoba held true only if that minimum mulch biomass benchmark of 6.7Mg ha−1 was reached.

Selecting Cover Crop Mulches for Organic Rotational No‐Till Systems in Manitoba, Canada

In western Canada, limited research has been conducted on reduced‐tillage grain production systems managed organically. The objective was to select cover crop mulches for an organic rotational no‐till system in Manitoba. A 2‐yr field study (2010–2011, and repeated 2011–2012) was conducted in Carman, MB, Canada. In the cover crop year, 10 different combinations of cover crop species were seeded in the spring, in pure stand or in mixtures, and rolled using a roller‐crimper in mid‐summer, at the flowering stage. These rolled mulches were then left on the soil surface over the fall and winter. The following spring, spring wheat (Triticum aestivum L.) was seeded directly into these mulches (no‐till). Mulches with hairy vetch (Vicia villosa Roth) showed the most promising results. Cover crop treatments with vetch had the highest mulch biomass in September of the cover crop year (9.1–10.7 Mg ha−1), and in the following spring (6.0–7.6 Mg ha−1) and provided the best weed control. In late fall of the cover crop year, N content of mulches with vetch reached high levels (308 kg N ha−1 on average), and high amounts of N (93–164 kg N ha−1) were released from these mulches over winter. Organic spring wheat no‐till planted into mulches with vetch produced yields comparable to regional conventional average yields. Mulches with vetch used in an organic rotational no‐till system reduced the need for tillage for a period of 1.5 to 2 yr without affecting yields of organic spring wheat.

Response of the common bean (Phaseolus vulgaris L.) to Tithonia diversifolia (Hamsl.) Gray biomass retention or removal in a slash and mulch agroforestry system

The addition of mulch biomass from Tithonia diversifolia (Hemsl.) Gray prior to seeding may improve bean production. We evaluated the response of two Costa Rican bean cultivars (Chirripo Rojo, Negro Huasetco) to the retention or removal of T. diversifolia biomass with respect to soil chemical characteristics, and bean biomass, nutrient content, root architecture, and fungal structures. There were no significant differences (p < 0.05) between bean cultivars and their influence on soil characteristics. Soil pH, Ca and Mg were significantly lower (p < 0.05) at bean harvest in both biomass removal and retention treatments compared to those at the time of bean sowing, whereas exchangeable acidity was significantly greater (p < 0.05) at bean harvest. Bean shoot nutrient concentration differed significantly between cultivars but not between biomass retention or removal treatments except for Mg. Pod, leaf and stem biomass, root characteristics, and the number of root fungal structures (entry points, vesicles, arbuscules) were significantly different (p < 0.05) between bean cultivars and mulch biomass treatments. Results showed that T. diversifolia biomass positively influenced bean shoot and root characteristics, and suggested that the addition of mulch may have added relatively large quantities of P and K to the soil and stimulated the uptake of these nutrients.

Production of Phaseolus vulgaris L. Genotypes with Tithonia diversifolia (Hemsl.) Gray and Cajanus cajan (L.) Millsp.

Adding mulch biomass prior to crop seeding may improve production of tropical soil. We evaluated the response of four bean (Phaseolus vulgaris L.) genotypes to the addition of mulch biomass from Tithonia diversifolia (Hemsl.) Gray and Cajanus cajan L. Millsp. The addition of mulch did not result in significant differences (p &lt; 0.05) in soil characteristics when compared to a control (no mulch addition) except for soil potassium (K), which was significantly greater (p &lt; 0.05) in the T. diversifolia mulch biomass treatment. Bean yield and shoot biomass were significantly greater (p &lt; 0.05) in the mulch biomass treatments compared to the control (no biomass added). In these treatments, Phosphorus (P)-efficient bean genotypes had a significantly greater (p &lt; 0.05) yield and shoot biomass. Bean shoot nutrient concentrations were significantly different (p &lt; 0.05) between mulch biomass treatments and between bean genotypes (P, K and magnesium (Mg) only). Phosphorus utilization and uptake efficiencies were significantly different (p &lt; 0.05) between mulch biomass treatments and between bean genotypes. Bean root biomass was not significantly different (p &lt; 0.05) between mulch biomass treatments, but was significantly different (p &lt; 0.05) between bean genotypes. The number of root nodules was significantly greater (p &lt; 0.05) in the T. diversifolia mulch biomass treatment and was significantly different between bean genotypes.

Nitrogen Dynamics and Nutrient Budgets in Four Orchard Groundcover Management Systems

Excessive nitrogen (N) applications can increase surface and water contamination, and leaching losses may occur when N fertilizer rates are too high relative to crop demands and soil N availability. Quantifying nutrient inputs, cycling, and outputs from orchards provides a method to measure surplus of nutrients, particularly N, that may leach or runoff. We conducted a long-term study to develop N budgets based on observed nutrient dynamics under four groundcover management systems (GMSs) with and without N fertilization. Four GMS treatments were randomly assigned to 12 plots and maintained since 1992 in 2-m-wide strips within tree rows: pre-emergence residual herbicide (PreHerb), post-emergence herbicide (PostHerb), mowed-sod (Sod), and hardwood bark mulch (Mulch). We measured system N inputs in fertilizer, mulch biomass, rain, and irrigation water; N outputs in harvested fruit, surface runoff, and subsurface leaching; and internal N cycling from surface vegetation, soil mineralization, leaf fall, and pruned wood. For the year with N fertilizer (2005), the overall N balance was positive (inputs exceeded outputs) in all GMSs but greater in the PostHerb and Mulch treatments. In the year without N fertilizer (2007), the overall N balance was negative for PreHerb and PostHerb and positive for Mulch and Sod treatments. Soil mineralization and recycling groundcover biomass accounted for greater than 60% of internal N fluxes, and harvested fruit represented greater than 70% of N outputs from the system during both years. During the year with N fertilizer, N losses were 1% to 4% and 18% to 22% through surface runoff and subsurface leaching, respectively. During the year without fertilizer, surface runoff N losses were twice the subsurface leaching N losses in all GMSs.

Effects of mulching materials on nitrogen mineralization, nitrogen availability and poplar growth on degraded agricultural soil

Nitrogen (N) is usually the most limiting nutrient in degraded agricultural soils and affects the growth and ecological function of poplar (Populus spp.) plantations. We hypothesized that application of organic mulch would improve soil nitrogen availability and increase tree growth, while the quality of mulching materials would alter the supply of essential nutrients. In this study, poplar plantations were established in 2004 and two experiments were established in the field. The fresh above-ground biomass of cogongrass (Imperata cylindrica (L.) P. Beauv.), oak (Quercus fabri Hance), Chinese coriaria (Coriaria nepalensis Wallich) and brackenfern (Pteridium aquilinum (L.) Kuhn. var. latiusculum (Desv.) Underw. ex Heller) in the current year was selected as mulching materials, and mulches were annually applied at the rate of 5.0 kg/m2 in the N mineralization experiment and 20,000 kg/ha in growth and nutrient availability experiment. Additions of fresh biomass significantly improved annual net N-mineralization estimates and the mulching treatments increased the cumulative N mineralized over the incubation period by 22–30%. However, a significant difference in the cumulative N mineralized was not observed among the mulched treatments, even if the cumulative N mineralized in the treatment mulched with oak (QF) was 5.9, 3.3 and 2.2% greater than that of treatments with brackenfern (PA), Chinese coriaria (CN) and cogongrass (IC), respectively. Application of fresh biomass mulch markedly affected soil available N contents and growth performance of poplar plantations. The mulching treatments with QF, IC, PA and CN increased annual means of available N concentration by 39.0, 29.0, 29.6 and 39.7% respectively. At the end of the fifth growing season, the average height of poplar plantations in treatments mulched with QF, IC, PA and CN was 46.8, 14.9, 42.6 and 57.4% greater than that in Check (CK-no mulch), while mean DBH increased by 35.4, 12.5, 33.3 and 52.1%, respectively. Overall, the productivity was enhanced in mulched plots at the end of the third growing season. Compared with CK, the treatments mulched with QF, IC, PA and CN increased total biomass by 97.4, 96.4, 63.1 and 81.6%, respectively. Based on the results of this study, annual application of 20,000 kg/ha fresh woody biomass would be recommended for soil improvement in young poplar plantations growing on a degraded agricultural soil.

Moisture conservation and nitrogen recycling through legume mulching in rainfed maize (Zea mays)–wheat (Triticum aestivum) cropping system

Mulching with vegetative materials is a highly beneficial and widely-investigated agro-technique in rainfed areas but the adoption of this practice has been constrained due to non-availability of mulch biomass locally. Live mulching with fast-growing annual green manure legumes like sunnhemp (Crotalaria juncea) or prunings of Leucaena leucocephala grown as hedge rows can be done for moisture conservation as well as nutrient cycling in the maize–wheat cropping system, which is predominantly followed in the high rainfall sub-mountainous region of north-western India. A field experiment was conducted at Selakui, Dehradun during 2000–2004 to study the effect of legume mulching, viz. in situ grown sunnhemp and Leucaena prunings, along with varying N levels, viz. 0, 30, 60 and 90 kg N ha−1 (to maize), and 0, 40 and 80 kg N ha−1 (to wheat) on productivity, soil moisture conservation and soil physico-chemical properties. Intercropped sunnhemp added 0.75–1.45 t dry matter and 21.6–41.3 kg N ha−1 at 30–35 days, while Leucaena twigs added 1.89–4.15 t dry matter and 75.2–161.3 kg N ha−1 at 60–65 days of maize growth. Live mulching with sunnhemp or Leucaena biomass improved soil moisture content at maize harvest (+1.15–1.57%) and crop productivity by 6.8–8.8% over no mulching. Combined use of both the mulching materials was more effective in improving the soil moisture content (+2.08–2.29%) and grain yield (15.1%) over their single application. Response of maize to N fertilizer application was significant up to 90 kg N ha−1, and it was relatively more pronounced under the mulching treatments. Residual effect of mulching on wheat showed an increase in yield of 10.2% with sunnhemp or Leucaena, and 27.9% with sunnhemp + Leucaena. There was an improvement in organic C and total N status of soil, and a decrease in bulk density associated with an increase in infiltration rate due to mulching at the end of 4 cropping cycles. It was concluded that legume mulching is a highly beneficial practice for enhanced moisture and nutrient conservation, leading to increased productivity and soil health of maize–wheat cropping system under Doon valley conditions of north-western India.

Tuber quality of edible potato fertilized with catch crops and barley straw

The work presents research results from the years 2000–2003. The research aimed to examine the possibilities of replacing farmyard manure, in edible potato cultivation, with catch crops and barley straw without reducing the level and quality of the tuber yield. Two factors were examined. I. Catch crop fertilization: a control object, farmyard manure, undersown catch crop (red clover, red clover + Italian ryegrass), stubble catch crop – biomass incorporated in autumn (fodder radish), stubble catch crop overwintering biomass mulch (fodder radish). II. Straw fertilization: straw-fertilized sub-block, a not-straw-fertilized sub-block, a not-straw-fertilized subblock. Undersown catch crops were sown after planting barley cultivated for grain whereas stubble catch crops were planted after barley harvest. Edible potato was cultivated in the first year after organic fertilizer application. The following characteristics were determined during potato harvest: commercial yield, starch, vitamin C, true protein and glycoalkaloid contents in the tuber samples. The conditions of the growing season significantly modified the commercial yield and the chemical composition of potato tubers. The highest commercial yield of potato tubers with the highest of starch, vitamin C, true protein, and the lowest of glycoalkaloid content was harvested from the treatment fertilized with either a mixture of red clover and Italian ryegrass, or red clover in combination with straw. Moreover, positive results were obtained when a fodder radish mulch + straw combination was applied.

Effectiveness and Efficacy of Conservation Options after Potato Harvest

Soil erosion and phosphorus (P) runoff can be severe in potato production systems in the Northeast USA, which are characterized by intensive tillage, minimal ground cover, low crop residue return, and steep slopes. We used rainfall simulators in the greenhouse and field to assess sediment and P movement associated with two conservation practices: straw mulching and application of polyacrylamide (PAM). In the greenhouse, a Nokomis sandy loam soil (fine-loamy, mixed, frigid Typic Haplorthods) was packed into 0.2 by 1.0 m boxes and subjected to four rainfall events at an intensity of 70 mm h(-1). Runoff amount, sediment concentration, and inorganic and sediment-bound P were measured for 30 min after initiation of runoff. Linear increases in straw mulch biomass (up to equivalent of 3000 kg ha(-1)) resulted in exponential decreases in sediment and P loss. Mulch applied at rates as low as 600 kg ha(-1) provided nearly 50% ground cover and reduced sediment movement and sediment-bound P concentration and loss by >50%. Higher application rates reduced sediment loss by up to 95% but contributed dissolved reactive P (DRP) to runoff water. Field observations using simulated rainfall on mulch-covered and bare soil were consistent with greenhouse results. Linear increases in PAM application rate (to 20 kg ha(-1)) also reduced sediment loss. The efficacy of this practice decreases slightly with successive rainfall events but still had significant benefit through four simulated rainfalls on soil packed into boxes. This was not the case in the field where the effect of PAM was limited to the first two rainfall events. In general, runoff volume was not strongly influenced by any of these practices, and most of the P loss was comprised of sediment-bound P. Both conservation practices are effective at reducing soil and nutrient loss in intensive potato systems.

Evapotranspiration of irrigated and rainfed maize–soybean cropping systems

We have been making year-round measurements of mass and energy exchange in three cropping systems: (a) irrigated continuous maize, (b) irrigated maize–soybean rotation, and (c) rainfed maize–soybean rotation in eastern Nebraska since 2001. In this paper, we present results on evapotranspiration (ET) of these crops for the first 5 years of our study. Growing season ET in the irrigated and rainfed maize averaged 548 and 482 mm, respectively. In irrigated and rainfed soybean, the average growing season ET was 452 and 431 mm, respectively. On average, the maize ET was higher than the soybean ET by 18% for irrigated crops and by 11% for rainfed crops. The mid-season crop coefficient K c (=ET/ET 0 and ET 0 is the reference ET) for irrigated maize was 1.03 ± 0.07. For rainfed maize, significant dry-down conditions prevailed and mid-season K c was 0.84 ± 0.20. For irrigated soybean, the mid-season K c was 0.98 ± 0.02. The mid-season dry down in rainfed soybean years was not severe and the K c (0.90 ± 0.13) was only slightly lower than the values for the irrigated fields. Non-growing season evaporation ranged from 100 to 172 mm and contributed about 16–28% of the annual ET in irrigated/rainfed maize and 24–26% in irrigated/rainfed soybean. The amount of surface mulch biomass explained 71% of the variability in non-growing season evaporation totals. Water use efficiency (or biomass transpiration efficiency), defined as the ratio of total plant biomass ( Y DM) to growing season transpiration ( T) was 5.20 ± 0.34 and 5.22 ± 0.36 g kg −1, respectively for irrigated and rainfed maize crops. Similarly, the biomass transpiration efficiency for irrigated and rainfed soybean crops was 3.21 ± 0.35 and 2.96 ± 0.30 g kg −1. Thus, the respective biomass transpiration efficiency of these crops was nearly constant regardless of rainfall and irrigation.

Growth and yield of maize alley cropped with Leucaena leucocephala and Faidherbia albida in Morogoro, Tanzania

This study examined the effect of alley cropping of Leucaena leucocephala and Faidherbia albida on wood biomass, maize grain yield and soil nitrogen status. The treatments were: trees planted alone at 1 × 5 m spacing; trees intercropped with maize and a sole maize crop. Mulch biomass averaged 6.18 and 0.97 t ha−1 for L. leucocephala and F. albida, respectively. Corresponding wood production was 1.71 and 1.11 t ha−1. Both total N and inorganic N (NO 3 − –N plus 4 + –N) were higher under F. albida and lowest under L. leucocephala. Similarly, foliar N concentration in maize was higher in plots intercropped with F. albida and least in L. leucocephala intercropping. Maize grain yield was little affected by the tree intercrop as competition for resources was reduced through periodic pruning and clean weeding. There was no gain in maize grain yield due to the presence of L. leucocephala and F. albida. These results suggest that alley cropping in Gario is justified for wood production but not for increasing maize grain yield.

Groundcover Management Systems Influence Fungicide and Nitrate-N Concentrations in Leachate and Runoff from a New York Apple Orchard

Commercial apple (Malus domestica Borkh.) orchards in the northeastern United States receive heavy pesticide inputs and are often located on well-drained soils near surface and groundwater resources. Nonpoint-source water pollution by agrichemicals has been monitored in agronomic crop systems and simulated using computer models and laboratory soil columns, but inadequately studied at field scale in orchards. We monitored the concentrations of agrichemical tracers, nitrate-N, and benomyl fungicide in water samples from two apple orchards under mowed sodgrass (Mowed-Sod), shredded bark mulch (Bark-Mulch), preemergence residual herbicides (Resid-Herb), and postemergence herbicide (Post-Herb) groundcover management systems (GMSs). In one orchard, we evaluated subsurface spatial patterns and flow rates of a weakly adsorbed blue dye (pesticide analog) and potassium bromide (nitrate analog) under trees after six years of Post-Herb and Mowed-Sod treatments. Nitrate and pesticide tracers leached more rapidly and in higher concentrations under Post-Herb treatments, apparently via preferential macropore flowpaths such as root channels, soil cracks, and macrofauna burrows. At another orchard, we monitored subsurface leaching and surface runoff of benomyl and nitrate-N on a whole-field scale. Peak concentrations of benomyl (up to 29 mg·liter-1) and nitrates (up to 20 mg·liter-1) were observed in subsoil leachate under Resid-Herb plots during 1993. In 1994, nitrate concentrations were greater in leachate from all GMSs, with upper ranges from 48 to 66 mg·liter-1, while benomyl concentrations were lower in all GMSs compared with the previous summer. In surface water runoff during 1993, the highest benomyl concentrations (387 mg·liter-1) and most frequent outflows occurred in Resid-Herb plots. During 1994, benomyl runoff was more frequent in both herbicide GMSs, with concentrations up to 61 mg·liter-1 observed in the Post-Herb plots. Weather patterns, irrigation intensity, differing soil conditions under each GMS, and the turfgrass/clover drive lanes affected the relative frequency and concentrations of benomyl and nitrate leaching and runoff. Preferential bypass flow appeared to be a major subsurface leaching pathway, and erosion sediment an important factor in surface movement of these agrichemicals. Our studies suggest that nitrate-N and benomyl fungicide may be more prone to leaching or runoff from orchard soils under some herbicide GMSs in comparison with mowed sodgrass or biomass mulch systems.

Yield, Earliness, and Fruit Weight of Fresh-market Tomatoes Grown in Synthetic and Organic Mulches

Fresh-market tomatoes (Lycopersicon esculentum Mill) cvs. Sunny and Sunbeam were grown in bare soil (BS), Horto paper (HP), black polyethylene (BP), hairy vetch (HV), crimson clover (CC), and hairy vetch plus rye (HVR) mulches. Yields were highest in HV (85.8 t·ha–1), followed by HVR 69.3 t·ha–1) and CC (65.7 t·ha–1), and averaged 47% above BP for the 3-year period. A 5- to 9-day earliness was exhibited by BP over other treatments. Fruit weight was significantly higher in all three organic mulch treatments than in the other three treatments. Mulch biomass was highest in HVR (5.91 t·ha–1), whereas N fixation was highest in HV (188 kg·ha–1). Tomato harvest was extended by the HV treatment over the BP treatment by 3 to 4 weeks, during which tomato prices were higher than those in early or mid-season.