More rows, more beans
RESEARCH TRIALS CONTINUE to show that planting mungbeans on rows no wider than 50 cm apart will provide an average 10–12 per cent yield bene t In addition, there appears to be no detrimental effect on insect, disease or weed management, or on harvestability Queensland Department of Agriculture and Fisheries senior extension agronomist, Kerry McKenzie, Toowoomba, said that row spacings of 25 cm have given peak yields in all situations with all crops in all seasons “We have had mungbean crops yielding up to 2 5 t ha and down to 0 5 t ha, but in all those situations it is the narrow rows that have given the best yields,” he said Mr McKenzie said although it wasn’t always practical for farmers to sow on rows as narrow as 25 cm, any reduction in row spacings would be bene cial “The peak yields have always come at 25 cm row spacing, but 50 cm is a good compromise There is always a compromise in a farming system with what you can and can’t do with things like machinery and stubble loads, so whatever you can do to get your rows closer together is going to give a yield increase,” he said Mr McKenzie said with earlier work con rming that narrow row spacings produced higher yields, he was now looking into why those crops were yielding more and where that yield was coming from “We have trials looking at biomass production at 25 cm and 50 cm spacing, under irrigated and dryland systems, and how well that biomass converts to yield, or in other words, what is the harvest index,” he said Mr McKenzie said time of sowing trials last year found a signi cant difference in yield for crops sown at the start of December, mid-January and the start of February “We got the best yields with the mid-January planting Even though the third planting in February produced more biomass it didn’t convert to extra yield,” he said “I think one of the reasons is the February-planted crop was owering in April and harvested in May when it ran into cool weather A lot of the daily minimum temperatures were below 15 degrees and we weren’t able to convert that extra biomass into yield ” Provided the temperatures stay warm, mungbean crops are able to produce a harvest index of around 0 to 0 5 and don’t appear to have a ceiling to the harvest index like chickpeas do This means whatever a grower can do to increase biomass production will generate more yield High biomass crops are also known to compete strongly with weeds and suppress weed seed set and are less prone to powdery mildew In addition, these high biomass crops x more nitrogen, leaving more behind after harvest To investigate where in the pro le mungbean plants draw water from, Mr McKenzie is running trials with neutron probes in selected plots on 25 cm and 1 m rows There are two probes per plot looking at water extraction on the row and in the inter-row area “Last year we found that the 25 cm rows always yielded better and extracted slightly more water,” he said “In the 1m row spacing there was more water being extracted from the top layers in the interrow than from the top layers in the row, down to about 50 cm We think this water is being lost to evaporation from the soil surface in the wider interrow ” One surprise nding has been that this fast growing crop is still extracting water from as deep as 105 cm in dryland and irrigated crops, much deeper than the 60 cm depth that had been previously thought Trials investigating plant population have con rmed that aiming to establish 20 to 0 plants per m2 is still a good rule of thumb in dryland situations, but if there is a problem with establishment and the grower is left with an even stand of at least 10 plants per m2 there is minimal loss of yield “When considering mungbeans in the rotation, keep in mind that mungbeans are susceptible to the main root-lesion nematode (RLN) species, Pratylenchus thornei,” said Mr McKenzie “The mungbean crop does not suffer yield loss but, if present, numbers will build up under the mungbean crop and may adversely affect the following crop ” RLN can cause yield losses as high as 70 per cent in intolerant varieties of wheat so growers are encouraged to test their soil for RLN and to factor this in when they are choosing wheat varieties for the following winter More information: www mungbean org au