Dry season groundnut stover management practices determine nitrogen cycling efficiency and subsequent maize yields

It is generally thought that grain legume residues make a substantial net N contribution to soil fertility in crop rotation systems. However, most studies focus on effects of residues on crops immediately sown after the legume crop while in fact in many tropical countries with a prolonged dry season there is a large gap before planting the next crop with potential for nutrient losses. Thus the objectives of this study were* to improve the efficiency of groundnut (Arachis hypogaea L.) stover-N (100 kg N ha ^–1) recycling by evaluating the effect of dry season stover management, i.e. surface application and immediate incorporation after the legume crop or storage of residues until next cropping in the rainy season. N dynamics (litterbags, mineral N, microbial biomass N, N ₂O emissions) were monitored and ¹⁵N labelled residues were applied to assess the fate of residue N in the plant–soil (0–100 cm) system during two subsequent maize crops. Recycling groundnut stover improved yield of the subsequent maize (Zea mays L.) crop compared to treatment without stover. A higher N recycling efficiency was observed when residues were incorporated (i.e. 55% total ¹⁵N recovery after second maize crop) than when surface applied (43% recovery) at the beginning of the dry season. This was despite the faster nitrogen release of incorporated residues, which led to more mineral N movement to lower soil layers. It appears that a proportion of groundnut stover N released during the dry season was effectively captured by the natural weed population (54–70 kg N ha ^–1) and subsequently recycled particularly in the incorporation treatment. Despite the presence of weeds major leaching losses occurred during the onset of the rainy season while N ₂O emissions were relatively small. There was a good correlation between soil microbial biomass N and first crop maize yield. Incorporation of groundnut residues led to small increases in economic yield, i.e., 3120 versus 3528 kg ha ^–1 over two cropping cycles in the surface versus incorporation treatments respectively, with corresponding residue ¹⁵N uptakes of 4 and 8%, while ¹⁵N recovery in water stable aggregates (9–15%) was not significantly different. In contrast, when stover was removed and applied before the first crop, yield benefits were highest with cumulative maize yields of 4350 kg ha ^–1 and residue utilization of 12%. However, N recycling efficiency was not higher than in the early incorporation treatment due to an asynchrony of N release and maize N demand during the first crop.     

Comparison of five DNA extraction methods for molecular analysis of Jerusalem artichoke (Helianthus tuberosus)

DNA extraction is an essential step for molecular analysis of an organism, but it is difficult to acquire a sufficient amount of pure DNA from plant tissue with high levels of phenolic compounds, carbohydrates, proteins, and secondary metabolites. Jerusalem artichoke (Helianthus tuberosus) has high levels of such substances. We compared five commonly used methods of extracting genomic DNA in tests made with leaves and seed of four Jerusalem artichoke genotypes: 1) modified method of Tai and Tanksley, 2) method of Doyle and Doyle, 3) method of Porebski, 4) modified method of ?torchová, and 5) Plant DNA Kit of Omega Bio-tek. The quality and quantity of extracted DNAs were assessed by photometric assay, electrophoresis on 1% agarose gel and a PCR-based technique. The modified method of Tai and Tanksley was found to be superior for both young leaves and seed. The quality of the extracted DNA was confirmed by sequence-related amplified polymorphism. This information will be useful for molecular analyses of Jerusalem artichoke and other related Helianthus species.     

Genetic diversity of worldwide Jerusalem artichoke (Helianthus tuberosus) germplasm as revealed by RAPD markers

Jerusalem artichoke (Helianthus tuberosus) is a wild relative of the cultivated sunflower (H. annuus); it is an old tuber crop that has recently received renewed interest. We used RAPD markers to characterize 147 Jerusalem artichoke accessions from nine countries. Thirty RAPD primers were screened; 13 of them detected 357 reproducible RAPD bands, of which 337 were polymorphic. Various diversity analyses revealed several different patterns of RAPD variation. More than 93% of the RAPD variation was found within accessions of a country. Weak genetic differentiation was observed between wild and cultivated accessions. Six groups were detected in this germplasm set. Four ancestral groups were found for the Canadian germplasm. The most genetically distinct accessions were identified. These findings provide useful diversity information for understanding the Jerusalem artichoke gene pool, for conserving Jerusalem artichoke germplasm, and for choosing germplasm for genetic improvement.     

Bio-control of Stem Rot in Jerusalem Artichoke (Helianthus tuberosus L.) in Field Conditions

Stem rot is a serious disease in Jerusalem artichoke (JA). To reduce the impact of this disease on yield and quality farmers often use fungicides, but this control method can be expensive and leave chemical residues. The objective of this study was to evaluate the efficacy of two biological control agents, Trichoderma harzianum T9 and Bacillus firmus BSR032 for control of Sclerotium rolfsii under field conditions. Four accessions of JA (HEL246, HEL65, JA47, and JA12) were treated or notreated with T. harzianum T9 and B. firmus BSR032 in a 4 × 2 × 2 factorial experiment in two fields (environments), one unfertilized and one fertilized. Plants were inoculated with S. rolfsii and disease was evaluated at 3-day intervals for 46 days. T. harzianum T9 and B. firmus BSR032 reduced disease incidence by 48% and 49%, respectively, whereas T. harzianum T9 + B. firmus BSR032 reduced disease incidence by 37%. The efficacy of T. harzianum T9 and B. firmus BSR032 for control of S. rolfsii was dependent on environments and genotypes. The expression of host plant resistance also depended on the environment. However, HEL246 showed consistently low disease incidence and severity index in both environments (fertilized and unfertilized). Individually, T. harzianum T9, B. firmus BSR032, or host plant resistance control stem rot caused by S. rolfsii in JA. However, no combination of these treatments provided more effective control than each alone.     

Seasonal variation in photosynthesis performance of cassava at two different growth stages under irrigated and rain-fed conditions in a tropical savanna climate

Photosynthetica - Seasonal variations in photosynthesis of cassava cv. Rayong 9 (RY9) under irrigated and rain-fed conditions were evaluated at the age of three and six months after planting (MAP)....