Impact of different cover crops and termination methods on collard yield

Haitian farmers depend on tillage and hand weeding for managing weeds in vegetable crops due to limited financial resources for purchasing herbicides and loss of laborers to urban migration. The use of cover crops was proposed as a means of suppressing weeds and plant-parasitic nematodes during the off-season before planting vegetable crops. The objectives of the study were to compare the effects of leguminous cover crops on weed and root-knot nematode ( Meloidogyne spp.) suppression before and during a subsequent eggplant ( Solanum melongena ) cash crop and evaluate the effects of the cover crops and supplemental fertilizer on eggplant growth and yield. In Summer 2018, three legume cover crops, velvet bean ( Mucuna pruriens ), cowpea ( Vigna unguiculata cv. Iron Clay), and sunn hemp ( Crotalaria juncea cv. Tropic Sun), and a no cover crop control were evaluated at Camp-Perrin and Ducis, Haiti. Cover crops were assigned to the main plots of a split-plot experimental design and ‘Florida Market’ eggplant with or without supplemental mineral fertilizer comprised the subplot treatments. Data were collected on cover crop shoot biomass accumulation, weed and plant-parasitic nematode suppression, and eggplant growth and yield. Cover crop fresh shoot biomass with sunn hemp and cowpea was higher than velvet bean at Camp-Perrin and sunn hemp biomass was higher than cowpea and velvet bean at Ducis. However, both sunn hemp and cowpea resulted in lower weed biomass than the weedy control during the cover crop phase. During the eggplant crop, only sunn hemp reduced weed biomass to less than the control. Sunn hemp produced the tallest eggplant plants with the highest shoot biomass and fruit yields, and fruit size was larger with sunn hemp than with the weedy control. Plant-parasitic nematode populations were low at both sites and not significantly different from the control. The results indicate that sunn hemp can be used as a cultural weed management method to suppress weeds and enhance eggplant yield in Haiti.

Tropical fruit production has become a lucrative industry in Miami-Dade County. Consequently, developing sustainable farming practices to be applied to these systems to ensure healthy soils and economically viable fruit production is becoming increasingly important. The study is focused on the incorporation of cover cropping as a management strategy for perennial tropical fruit production and its applications for local growers. Cover crops are plants that are grown to cover soil to reduce erosion, increase soil fertility, and enhance farmland biodiversity. The project was specifically designed to test the impacts of highly prolific legumes sunn hemp (Crotalaria juncea) and velvet bean (Mucuna pruriens), intercropped with young carambola (Averrhoa carambola) trees on soil and plant health parameters. Sunn hemp and velvet bean were grown for two 90-day growing seasons and were left to decompose as green manure after termination. Carambola trees and surrounding soil were monitored over a 1.5-year period to quantify changes among six fertilizer treatments. Along with the field study, surveys were formulated and distributed to local growers to assess likelihood of cover crop adoption within the community. The goals of this work are threefold: 1) to understand the impact of legume cover crops on soil parameters 2) to understand the interaction between legume cover crops and carambola health/fruit production 3) to understand the perceptions of local fruit producers concerning cover cropping as a management strategy. Results indicated that sunn hemp was most successful in biomass production and providing available nitrogen to soils, while velvet bean was most stimulatory for short-term soil microbial parameters. Sunn hemp treatments were comparative to poultry manure fertilizer for contribution of soil carbon and nitrogen over the sampling period. Trees treated with sunn hemp exhibited high fruit yields and exceeded other treatments in regard to tree health parameters. Surveys conducted amongst the Miami-Dade County agriculture community revealed that farmers were interested in learning about cover cropping and attending workshops and informational sessions. Through logistic regression analysis, likelihood to cover crop was positively influenced by farm size, previous experience with cover crops, believing the practice is economically viable, and valuing cover crop importance.

Crop rotation associated with the use of cover crops promotes the introduction of crop residues to the soil, with direct and indirect effects on the availability of plant nutrients, especially nitrogen (N). The objectives of this study were to estimate the N utilization from 15N-urea and cover crop residues (labelled with 15N) of maize crops grown in succession, and evaluate the effects of the isolated and combined use of cover crops and urea on maize plant height, yield components, and grain yield, grown under a no-tillage system. Field research was conducted in an Oxisol (Rhodic Haplustox), Cerrado (Savannah) phase. The experimental design was a randomized block with 20 treatments and four replications in a 5x4 factorial scheme. The treatments were four cover crops species: sunn hemp (Crotalaria juncea L.), pigeon pea (Cajanus cajan (L.) Millsp), green velvet bean (Mucuna prurens), and millet (Pennisetum glaucum L.) + spontaneous vegetation (fallow in the off-season), combined with four N rates: 0, 30, 90, and 150 kg ha-1, applied at the sowing and topdressing stages. The results showed that legume cover crops provided maize grain yields equivalent to the application of 80-108 kg ha-1 N as urea. The urea N utilization by the maize was at an average of 43.5 % of the applied amount. The results indicate that cover crops, particularly legume cover crops, are an important source of N to non-legume cereals. Legumes used as cover crops can replace nitrogen fertilizers of more than 80 kg ha, which is both environmentally and economically viable for corn production.

South Florida’s agricultural soils are traditionally low in organic matter (OM) and high in carbonate rock fragments. These calcareous soils are inherently nutrient-poor and require management for successful crop production. Sunn hemp (SH, Crotalaria juncea) and velvet bean (VB, Mucuna pruriens) are highly productive leguminous cover crops (CCs) that have shown potential to add large quantities of dry biomass to nutrient- and organic-matter-limited systems. This study focuses on intercropping these two CCs with young carambola (Averrhoa carambola) trees. The objective was to test the effectiveness of green manure crops in providing nutrients and supplementing traditional fertilizer regimes with a sustainable soil-building option. Typically, poultry manure (PM) is the standard fertilizer used in organic or sustainable production in the study area. As such, PM treatments and fallow were included for comparison. The treatments were fallow control (F), fallow with PM (FM), sunn hemp (SH), SH with PM (SHM), velvet bean (VB), and VB with PM (VBM). Sunn hemp and VB were grown for two summer growing seasons. At the end of each 90-day growing period, the CCs were terminated and left on the soil surface to decompose in a no-till fashion. The results suggest that SH treatments produced the greatest amount of dry biomass material ranging from 48 to 71% higher than VB over two growing seasons. As a result, SH CCs also accumulated significantly higher amounts of total carbon (TC) and total nitrogen (TN) within their dry biomass that was added to the soil. Sunn hemp, SHM, and FM treatments showed the greatest accumulation of soil OM, TC, and TN. Soil inorganic N (NH₄⁺ + NO3− + NO2) fluctuated throughout the experiment. Our results indicate that generally, VB-treated soils had their highest available N around 2 months post termination, while SH-treated soils exhibited significantly higher N values at CC termination time. Sunn hemp + PM (SHM)treatments had highest soil N availability around 4 months after CC termination. Soil enzyme activity results indicate that at CC termination, SHM exhibited the highest levels of β-1-4- glucosidase and β-N-acetylglucosaminidase among all treatments. Overall, SH, SHM, and FM treatments showed the greatest potential for supplementing soil nutrients and organic matter in a no-till fruit production setting.

Soil compaction is a main physical problem in many growing areas. The use of ground cover crops for soil decompaction has been a subject of many studies. That has promising results both used alone and in association with mechanical chiseling. The objective of this study was to evaluate the influence of cover crops associated or not with mechanical chiseling, for that, on the physical attributes of the soil, and the wheat grain yield, in an Ultisol from the Central Depression of RS. The experimental design used was randomized blocks with 3 replications in each block, in a 2 x 5 factorial scheme. Where the factor A: soil chiseling - chiseled and non-chiseled, and P fator: cover crops – pigeon pea (Cajanus cajan), Crotalaria juncea (Crotalaria juncea), pearl millet (Pennisetum americanum) and velvet bean (Mucuna aterrima). The chiseling was adjusted to a depth of 0.30m, with 5 rods spaced 0.3m apart. The determinations carried out were: macroporosity, microporosity, total soil porosity, bulk density (BD), penetration resistance (RP), and grain yield. The physical attributes of the soil showed improvements in the second year evaluated, highlighting the treatments with pearl millet and velvet bean that showed higher differences. The maximum RP of the Soil was observed at a depth of 0.25m with 1.64 Mpa. There was a significant difference in the RP of the soil between the treatments of factor A at depths of 0.15 - 0.20 and 0.25m. Mechanical chiseling provided a 15% increase in wheat grain yield compared to non-chiseling treatment, while P factor treatments did not provide any gain.

In recent years, the growth of the cultivated area with sweet corn in conventional tillage system in Brazil expanded, although crops can be grown on different residues of cover crops, which improve nutrient cycling and crop productivity. The objective of this study was to evaluate the biomass production and to quantify the rate of plant residues decomposition of different cover crops, and correlate the results with the production and grain yield of sweet corn in an area located in the Cerrado biome. The experimental design used was randomized blocks with eight treatments: PM - pearl millet; SH - sunn hemp; SG - signal grass; PM + SH; PM + SG; SH + SG; PM+ SH + SG; FW - fallow (spontaneous vegetation), which preceded the cultivation of sweet corn. Fresh biomass (FB) and dry biomass (DB) of the cover crops were evaluated, as well as the rate of plant residue decomposition. Sweet corn productivity, straw and corncob weight, and grain yield were also determined. Pearl millet presented a better performance in FB production, decomposition rate, residue half-life (T½ life) in soil, yield, corn cob strawweight and yield of sweet corn. Pearl millet, when mixed with other plants, presented reduced rate of residue decomposition and increased residue T½ life. The FW presented the lowest biomass production, with great rate of decomposition and low T½ life. Cover crops grown before sweet corn in soils of good fertility did not affect crop agronomic characteristics. Pearl millet is the best cover crop adapted to Cerrado Brazilian climatic conditions to be used in monoculture or in mixtures with other plants.

Core Ideas Cover crop (CC) biomass production across temperate regions averaged 3.37 ± 2.96 Mg ha−1.Ten high‐biomass producing CCs in temperate ecoregions were in this order: sorghum > sunn hemp > millet > rye > mixes > crimson clover > barley = hairy vetch > annual ryegrass > oat.Cover crop biomass production was greater in humid than semiarid regions and in areas with relatively high mean temperatures.Cover crop biomass production by cropping system was in this order: vegetables > other systems > maize > small grains.Cover crop biomass production generally increased with drill‐planting and increased seeding rate and growing season. Cover crop (CC) biomass production dictates agricultural and environmental services that CCs deliver, but finding a review on this topic is difficult. We synthesized published data on CC biomass production for 20 common CC species in temperate regions and discussed factors affecting CC biomass production. Review of 389 papers indicated CC biomass production was 3.37 ± 2.96 Mg ha−1 (mean ± SD). Cover crop biomass production for the top five biomass‐producing species was: sorghum (Sorghum sp.) (5.99 Mg ha−1) > sunn hemp (Crotalaria juncea L.) (5.77 Mg ha−1) > millet (Pennisetum glaucum L.) (4.95 Mg ha−1) > rye (Secale cereale L.) (4.93 Mg ha−1) > two‐species mix (4.18 Mg ha−1). In humid regions (>750 mm precipitation), CC biomass production ranged from 1.67 to 6.30 Mg ha−1 depending on species. In regions with <750 mm precipitation, CC biomass production ranged from 0.87 to 6.03 Mg ha−1. Cover crop biomass production was in this order by cropping system: vegetables > other systems [soybean (Glycine max L.), cotton (Gossypium hirsutum L.), and others] > maize (Zea mays L.) > small grains. Rye was among the most common and highest biomass producing species in most regions and cropping systems. Drill‐planting and maximizing CC growing season, such as early planting or late termination, can increase CC biomass production. Irrigation at establishment increased CC biomass production for legumes and mixes in humid regions, and all CC groups in semiarid regions. Overall, CCs can produce significant amount of biomass, but this can be highly dependent on climate, CC species, cropping system, and management.

In order to understand how soil microbial biomass was influenced by incorporated residues of summer cover crops and by water regimes, soil microbial biomass carbon (C) and nitrogen (N) were investigated in tomato field plots in which three leguminous and a non-leguminous cover crop had been grown and incorporated into the soil. The cover crops were sunn hemp (Crotalaria juncea L., cv ‘Tropic Sun’), cowpea (Vigna unguiculata L. Walp, cv ‘Iron clay’), velvetbean (Mucuna deeringiana (Bort) Merr.), and sorghum sudangrass (Sorghum bicolor × S. bicolor var. sudanense (Piper) Stapf) vs. a fallow (bare soil). The tomato crop was irrigated at four different rates, i.e., irrigation initiated only when the water tension had reached −5, −10, −20, or −30 kPa, respectively. The results showed that sorghum sudangrass, cowpea, sunn hemp, and velvetbean increased microbial biomass C by 68.9%, 89.8%, 116.8%, and 137.7%, and microbial N by 58.3%, 100.0%, 297.3%, and 261.3%, respectively. A legume cover crop, cowpea, had no statistically significant greater effect on soil microbial C and N than the non-legume cover crop, sorghum sudangrass. The tropical legumes, velvetbean and sunn hemp, increased the microbial biomass N markedly. However, the various irrigation rates did not cause significant changes in either microbial N or microbial C. Soil microbial biomass was strongly related to the N concentration and/or the inverse of the C:N ratio of the cover crops and in the soil. Tomato plant biomass and tomato fruit yields correlated well with the level of soil microbial N and inversely with the soil C:N ratio. These results suggest that cover crops increase soil microbiological biomass through the decomposition of organic C. Legumes are more effective than non-legumes, because they contain larger quantities of N and lower C:N ratios than non-legumes.

Modeling cover crop biomass production and related emissions to improve farm-scale decision-support tools

No-till vegetable farming is a feasible alternative to reduce erosion-induced losses and to increase soil nutrient availability, because cover crop residue protects the soil and its decomposition promotes nutrient cycling, which can improve the yield of the subsequent crop. The present study assessed the production and decomposition of cover crops and the agronomic performance of broccoli grown on this residue using different nitrogen doses in a no-till system. A randomized block design was used, in a split-split plot arrangement of main plots (cover crops), sub-plots (N doses) and sub-sub plots (decomposition times), with four repetitions. Seven cover crops were studied, as follows: [1) signal grass (SG); 2) sunn hemp (SH); 3) pearl millet (PM): 4) SG+SH; 5) SG+PM; 6) SH+PM and 7) SG+SH+PM]; in addition to four doses of nitrogen topdressing [T1) no N application (control); T2) 60 kg/ha N; T3) 90 kg/ha N and T4) 120 kg/ha N]; and five cover crop residue decomposition times: zero (cutting), 15, 30, 60 and 90 days after transplanting (DAT) the broccoli seedlings. Cover crop dry weight (DW) production, residue decomposition, and the head fresh (HFW) and dry weight (HDW) and yield (YLD) of broccoli were assessed. Among the cover crops, sunn hemp and the intercropped SG+SH treatment exhibited the lowest DW production and, along with signal grass, the shortest half-life (T½) and highest residue decomposition rate. The best-performing broccoli plants were those grown using PM, SH and a combination of both as cover crops. The highest broccoli production was obtained using sunn hemp residue, regardless of nitrogen topdressing, with HFW of 788 g/plant and YLD of 30 t/ha.

Special corn is cultivated all year conventionally round; however, its productivity increases when grown under a no-tillage system (NTS). This study aimed to evaluate the agronomic performance of sweet and green corn cultivated under residues of different cover crops and the NTS implantation stages. Two experiments were carried out in the randomized block design, with four replications, in each of the three areas. The experiments consisted of evaluating the sweet and green corn, simultaneously, in three areas at different stages of development of NTS: initial (1 year), transition (7 years), and consolidation (19 years) with six types of cover crops: Signal grass (SG), Pearl millet (PM), Sunn hemp (SH), a mixture of SG + SH, SG + PM, and PM + SH. The dry matter (DM) production of the cover crops, the productivity of husked and unhusked ears, straw, and grain yield were evaluated. The SH had the highest dry mass production among the studied cover crops in all phases of the NTS. The phase of the NTS did not influence the productivity of ears with or without husk in green corn. The cultivation of sweet corn in transition and consolidation areas of the NTS showed better yields when compared to the initial phase of the system.

Crambe oil yield and soil physical properties responses to no-tillage, cover crops and chiseling

Tropical legumes like sunn hemp (Crotolaria juncea L.) and aeschynomene (Aeschynomene evenia L.) have potential as alternative cover crops in tropical regions. The objective of this study was to evaluate the N mineralization rates of three cover crops [aeschynomene (AE), sorghum sudangrass (Sorghum sudanense L.), and sunn hemp (SH)] residues used to amend a calcareous gravelly soil in order to predict nitrogen (N) availability for uptake by subsequent crops. The soil amended with cover crop residues was incubated in columns under ambient and controlled temperatures. Mineralization rates were determined with a leaching/incubation method. The mineral N ratios between ambient and controlled temperature ranged from 1.39 to 2.8 with an average of 2.1. The measured cumulative mineral-N indicated that legumes were far more effective than non-leguminous cover crops in increasing N availability in the soil. The maximum values of mineral N recovered were 19, 7, and 8% of added N for AE, SH, and sorghum sudan (SS), respectively, when incubated at ambient temperature. Based on the Mean Square Error (MSE) for the equations describing mineralization kinetics, the power function was better than other models for all treatments, except SS at both the temperatures. The comparison of goodness of fit between the observed and predicted values indicated that the power function and parabolic equation produced generally good predictions for AE, SH, and control treatments at ambient temperature. However, at controlled temperature, the power function and the zero-order equations gave the best predictions for all treatments.

The residues of cover plants and crops left on the soil surface can influence decomposition, nutrient cycling and follow crop yield. The objective was to evaluate the production of dry biomass (BD), of residues decomposition rate and yield of maize and soybean grown on different soil covers. The experimental design was a randomized block scheme banded, with four covers: Brachiaria, sun hemp, pearl millet and fallow period in autumn/winter, with maize and soybean crop in the spring/summer. We evaluated BD, decomposition through bags of decomposition and yield of maize and soybeans. Pearl millet and sunhemp were the covers which produced more of BD in the fall/winter period. the rate of decomposition of plant residues in maize and soybeans is slow in the dry period and accelerated in the rainy period; maize yield was higher when grown on sunhemp and brachiaria in the years evaluated, while for soybeans there were no differences on any measured coverage; maize and soybeans have grain yields higher than the regional average when grown on different soil covers.

Agricultural practices, specifically crop and land management schemes, greatly influence the ability of soil to produce CO2 under varying conditions. A 2-year research study was planned to quantify carbon-dioxide (CO2) emission fluxes and total C (TC) contribution in a no-till tropical soil under carambola with sunn hemp-velvet bean cover cropping (CC) systems. Composted poultry manure (PM) was applied as an additional N source. The treatments were fallow control (F), fallow with PM (FM), sunn hemp (SH), SH with PM (SHM), velvet bean (VB), and VB with PM (VBM). Average daily CO2 emission from VB was 23 and 15% higher than control and SH plots, respectively, during CC growing season. Similarly, CO2 emission after CC termination was highest from VB plots. About 17% higher CO2-C emission was observed from manure applied plots which indicates that additional food sources stimulated microbial activity in the soils and subsequently produced more CO2. However, total C contribution in SH plots were significantly higher than in VB plots and was more apparent when manure was not applied. Soil and air temperature played key roles in CO2 emission, specifically during the CC growing season. Considering both input and output parameters of C in the soil, our results suggest that SH has the better potential in reducing CO2 emission and accumulating more C in the soil than VB in tropical fruit orchard.