Effects of Different Fumigants on the Replanted Soil Environment and Growth of Malus hupehensis Rehd. Seedlings

Apple replant disease (ARD) has been reported in all major fruit-growing regions of the world and is often caused by biotic factors (pathogen fungi) and abiotic factors (phenolic compounds). Soil chemical fumigation can kill soil pathogenic fungi; however, the traditionally used fumigant methyl bromide has been banned because of its ozone-depleting effects. There is thus a need to identify greener fumigant candidates. We characterized the effects of different fumigants on the replanted soil environment and the growth characteristics of Malus hupehensis Rehd. seedlings. All five experimental treatments [treatment 1 (T1), metham-sodium; treatment 2 (T2), dazomet; treatment 3 (T3), calcium cyanamide; treatment 4 (T4), 1,3-dichloropropene; and treatment 5 (T5), methyl bromide] promoted significantly the biomass, root growth, and root respiration rate of M. hupehensis seedlings and the ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3–-N) contents of replanted soil. Metham sodium (T1) and dazomet (T2) had stronger effects compared with 1,3-dichloropropene (T4) and calcium cyanamide (T3). At 172 days after T1, the height, root length, and root respiration rate of Malus hupehensis Rehd. seedlings, and the NH4+-N and NO3–-N contents of replanted soil increased by 91.64%, 97.67%, 69.78%, 81.98%, and 27.44%, respectively, compared with the control. Thus, dazomet and metham sodium were determined to be the optimal fumigants for use in practical applications.

Assessment of the potential of a reduced dose of dimethyl disulfide plus metham sodium on soilborne pests and cucumber growth

Methyl bromide (MB), a dominant ozone-depleting substance, is scheduled to be completely phased out for soil fumigation by December 30th 2018, in China. The combined effects of dimethyl disulfide (DMDS) plus metham sodium (MNa) were assessed in controlling soilborne pests for soil fumigation. A study was designed in laboratory for the evaluation of the efficacy of DMDS + MNa to control major soilborne pests. At the same time, two trials were conducted in cucumber field located in Tongzhou (in 2012) and Shunyi (in 2013), respectively, in order to assess the potential of DMDS + MNa in controlling soilborne pests. Laboratory studies disclosed positive synergistic effects of almost all four used combinations on Meloidogyne spp., Fusarium spp., Phytophthora spp., Abutilon theophrasti and Digitaria sanguinalis. Field trials found that DMDS + MNa (30 + 21 g a. i. m−2), both at a 50% reduced dose, effectively suppressed Meloidogyne spp. with a low root galling index (2.1% and 11.7%), significantly reduced the levels of Phytophthora and Fusarium spp. with a low root disease index (7.5% and 15.8%), gave very high cucumber yields (6.75 kg m−2 and 10.03 kg m−2), and increased income for cucumber growers with the highest economic benefits (20.91 ¥ m−2 and 23.58 ¥ m−2). The combination treatment provided similar results as MB standard dose treatment (40 g a. i. m−2) or DMDS standard dose treatment (60 g a. i. m−2) in pest control and yield, but was more effective than MNa standard dose treatment (42 g a. i. m−2). Usage of all chemical treatments gave better significant results than the untreated group of control. Considering the economic benefits, the DMDS plus MNa combination (30 + 21 g a. i. m−2) could be used for soil fumigation in cucumber production in China.

Effect of Field Treatment with Selected Soil Amendments on Bacterial Wilt Incidences in Tomatoes, Capsicum and Potatoes

Aims: The aim of this study was to establish the effect of field treatment with selected soil amendments on bacterial wilt incidences in Tomatoes, Capsicum and Potatoes. Study Design: The study was laid out as randomized complete block design (RCBD) in split plot arrangement for two seasons in the field. Place and Duration of Study: The experiment was conducted at the experimental plots at KARLO- NARL, Kabete Nairobi County between July, 2017- September, 2017 and between November, 2017- January, 2018. Methodology: The three choice crops of interest (potatoes, tomatoes and capsicum) were inoculated with prepared pure bacterial isolates; 18 (2T-Kiambu-Low Land), 71(2A-Nyeri-Low Land), 67 (2A-Nyeri-High Land), 83 (2T-Kirinyaga-Highland) and MX (18/71/67/83). A plot measuring 66 m by 28.5 m was marked, cleared, ploughed, harrowed and demarcated into 150 plots each measuring 2.4 m x 3.75 m. Spacing of the host crops of interest: potato - (Tigoni variety), tomato (Caj variety) and capsicum (Califonia Wonder) was carried out at 75 cm between the rows and 30 cm within the rows. The treatments were ChalimTM, Super-hydro-grow polymer + Metham sodium, Metham sodium, Metham sodium & Orange peel, Super-hydro-grow polymer, Brassica tissues, ChalimTM + Super-hydro-grow polymer, Brassica tissue + Orange peel, Metham sodium + Super-hydro-grow polymer and Control (no amendments). Results: Significant differences (P≤0.05) were revealed in the bacterial wilt incidences in tomatoes, capsicum and potatoes between control and all the soil amendments used in season 1 and 2 in the five R. solanacearum isolate from Kenyan highlands and lowlands. The Brassica tissue + Super-hydro-grow polymer was superior in reducing bacterial wilt incidences in tomatoes, capsicum and potatoes in the field in all the R. solanacearum isolates from Kenyan highlands and lowlands both in season 1 and 2. Conclusion: The findings showed that organic and inorganic soil amendments could serve as a viable control of bacterial wilt in solanaceous crops caused by R. solanacearum in the field. We recommend the use of Brassica tissue + Super-hydro-grow polymer soil amendment in the control of bacterial wilt incidences in the field on solanaceous crops.

Influence of Organic and Inorganic Soil Amendments on Soil Moisture Content and Micronutrients

Aims: This study was carried out to evaluate the influence of organic and inorganic soil amendments on soil moisture content and micronutrients in semi and arid areas. Methodology: The study was laid out as randomized complete block design (RCBD) in split plot arrangement for two seasons. The treatments were ChalimTM, Super-hydro-grow polymer and Metham sodium, Metham sodium, Metham sodium + Orange peel, Super-hydro-grow polymer, Control, Brassica tissue, ChalimTM + Super-hydro-grow polymer, Brassica tissue + Orange peel and Metham sodium + Super-hydro-grow polymer. Soils were sampled from each experimental site, dried and taken to laboratories for determination of Zinc, Iron, Manganese and copper both at initial and at the end of the experiment using a SpectrAA- 40 atomic absorption spectrometer, PSC-56 programmable sample changer. Moisture content was calculated by subtracting total dry soil plus Petri dish weight from total wet soil plus Petri dish weight. Calculated moisture content was recorded in all samples across the two seasons for analysis. Results: There was a significant difference (p≤0.05) in the treatment effect on soil moisture content in except for MS and CM+OP in both season one and season two in the green house. A combination of both organic and inorganic soil amendments like BT+OP, BT+ SHG had the highest moisture content. There was significant difference (p≤0.05) in the soil amendments effect on the amount of Micronutrients in the beginning and end of the experiement. Conclusion: Through this study, it was realized significant difference (p≤0.05) in the soil amendments effect on soil moisture content in all the treatment in both seasons. BT +SHG soil amendment was superior in maintaining soil moisture content in both season 1 and 2. It is therefore recommended that Metham sodium should not be applied in very dry soil to avoid reduction of the moisture content. There was micronutrient increment in all the treatments. BT+ SHG was superior soil amendment in increment of micronutrients.

Control of Ralstonia solanacearum on Selected Solaneceous Crops in Greenhouse by Selected Soil Amendments

Aims: The aim of this study was to establish the effect of selected soil amendments on Ralstonia solanacearum isolates in greenhouse on selected solaneceous crops. Study Design: The study was laid out as randomized complete block design (RCBD) in split pot arrangement for two seasons in the greenhouse. Place and Duration of Study: The experiment was carried out in Kenyattta University situated in Kiambu County about 20 km from Nairobi city along Nairobi-Thika road between July, 2017- September, 2017 and between November, 2017- January, 2018. Methodology: The three host crops of interest (potatoes, tomatoes and capsicum) were inoculated with prepared pure bacterial isolates; 18 (2T-Kiambu-Low Land), 71(2A-Nyeri-Low Land), 67 (2A-Nyeri-High Land), 83 (2T-Kirinyaga-Highland) and MX (18/71/67/83). Potatoes, tomatoes and capsicum were planted in pots each with a radius of 0.07 m (area 0.015 m2).The experiment had a total of 450 pots having a total area of 6.93 m2. The treatments were ChalimTM, Super-hydro-grow polymer + Metham sodium, Metham sodium, Metham sodium & Orange peel, Super-hydro-grow polymer, Brassica tissues, ChalimTM + Super-hydro-grow polymer, Brassica tissue + Orange peel, Metham sodium + Super-hydro-grow polymer and Control (no amendments). Results: There were significant differences (P≤0.05) in the bacterial wilt incidences in selected solaneceous crops between control and all the soil amendments used in season 1 and 2. Brassica tissue + Super-hydro-grow polymer was superior in reducing bacterial wilt incidences in selected solaneceous crops in all the R. solanacearum isolates from Kenyan highlands and lowlands both in season 1 and 2. Conclusion: Organic and inorganic soil amendments could serve as a viable control of bacterial wilt in solaneceous crops caused by R. solanacearum in the greenhouse.

Influence of Organic and Inorganic Soil Amendments on Soil pH and Macronutrients

The popularity of using the Inorganic and organic soil amendments is based on the current status of soil degradation that led to decline in fertility of soils, resulting to low yields. The objective of current study was to evalute different organic and inorganic soil amendments and their effects on soil pH and macronutrients. The study was laid out as randomized complete block design (RCBD) in split plot arrangement for two seasons. The treatments were ChalimTM, Super-hydro-grow polymer + Metham sodium, Metham sodium, Metham sodium & Orange peel, Super-hydro-grow polymer, Brassica tissues, ChalimTM + Super-hydro-grow polymer, Brassica tissue + Orange peel, Metham sodium + Super-hydro-grow polymer and Control (no amendments). Soils were sampled from each experimental site, dried and taken to laboratories for determination of soil chemical properties both at initial and at the end of the experiment. The soil physicochemical attributes assessed included: Soil pH, nitrogen, carbon, phosphorus, potassium and calcium. There was an significant increase (P≤0.05) in the concentration and availability of soil physicochemical characteristics after treatment which is an indicator of improved soil structure. Brassicae tissue +super hydrogrow polymer (BT+SHG) amendment was the best as it resulted to highest concentration and availability of the mineral elements in the soil recording total nitrogen of 0.50 %, organic carbon 5.47 %, phosphorus 19.7 mg/kg, and potassium 1.37 %. The control exhibited the least impact on all the soil chemical properties. We recommend BT+SHG amendment to farmers to promote soil fertility which will consequently produce better yield.

Allyl Isothiocyanate and Metham Sodium as Methyl Bromide Alternatives for Weed Control in Plasticulture Tomato

Isothiocyanates (ITCs) were evaluated as an alternative to methyl bromide (MeBr) for control of Palmer amaranth, large crabgrass, and yellow nutsedge; reduction of tuber density; and increase in marketable tomato yield in low density polyethylene (LDPE)-mulched tomato production. Allyl ITC was applied at 450, 600, and 750 kg ai ha−1; metham sodium (methyl ITC generator) was applied at 180, 270, and 360 kg ai ha−1; and MeBr plus chloropicrin (mixture of MeBr and chloropicrin at 67 : 33%, respectively) was applied at 390 kg ai ha−1. A nontreated weedy check was included for comparison. There was no injury to tomato plants following allyl ITC, metham sodium, or MeBr application. Allyl ITC at 750 kg ha−1or metham sodium at 360 kg ha−1controlled Palmer amaranth ≥ 79%, large crabgrass ≥ 76%, and yellow nutsedge ≥ 80% and was comparable to the weed control with MeBr. Highest rates of allyl ITC and metham sodium reduced yellow nutsedge tuber density (≤ 76 tubers m−2) comparable to the MeBr application. Total marketable tomato yield was ≥ 31.6 t ha−1in plots treated with allyl ITC at 750 kg ha−1or metham sodium at 360 kg ha−1. Marketable tomato yield from the highest rate of allyl ITC or metham sodium were similar to the yield (38.2 t ha−1) with MeBr treatment. Therefore, allyl ITC at 750 kg ha−1and metham sodium at 360 kg ha−1are effective alternatives to MeBr for Palmer amaranth, large crabgrass, and yellow nutsedge control in LDPE-mulched tomato.