Best Management Practices for Growing Maize on Dairy Farms

3. HybridThere are many different maize hybridsavailable. The main differences betweenhybrids are:• The number and size of leaves (whichaffects green leaf area and henceradiation interception).• Crop maturity or the number of GDD’sbe<strong>for</strong>e the crop is ready to harvest.• Their ability to cope with stresses suchas disease or drought.Your choice of hybrid will ultimately dependon; where you are, when you want to sow,and when you want to harvest. Your seedsales representative can help you select asuitable hybrid.As a general guide, short season hybridstend to yield less because they have fewerand smaller leaves than long seasonhybrids (intercept less radiation). They alsoneed fewer GDD’s to reach maturity, sothey are in the ground <strong>for</strong> fewer days, andhence absorb less radiation.4. Plant populationPopulation affects radiation interception asmore plants means more leaf area. Typicalpopulations <strong>for</strong> maize silage is 100 to 120thousand (K) seeds per hectare (there are80 K seeds in a bag) and your seed salesrepresentative will advise you on the bestpopulation <strong>for</strong> your situation. Final populationsare normally 5 K/ha less than whatwas originally sown.Other factors affecting potential yieldPotential yield assumes there is no limitationto the stresses that commonly affectmaize yields. In reality, this is seldom true.Weed pressure can reduce maize yield byup to 30%, make harvest difficult and contaminatesilage. Monitor crops <strong>for</strong> weedsand take action early as many weeds cangrow faster than maize seedlings.Drought will reduce maize yield by 22 kgDM/ha <strong>for</strong> every 1 mm of potential soilmoisture deficit (the difference betweenwhat a crop needs and what it gets).Because maize has deep roots (up to 1.8m), few maize crops are irrigated exceptif grown in dry environments and/or onshallow soils.Water logging reduces the plant’s abilityto take up nutrients, and creates a toxic soilenvironment <strong>for</strong> plant roots, since the soilcannot ‘breathe’ and release gases createdby soil microbial activity. Prolonged waterlogging can cause large losses in maizeyields.The nutrient requirements <strong>for</strong> maize willbe covered in chapter six. The nutrientmost likely to limit maize yields is nitrogen.Soil nitrogen is generally low in paddockswith a long history of cropping, but veryhigh in paddocks coming out of long termpasture.The main leaf diseases of maize arecommon rust, eyespot and northern cornleaf blight. Severe infection can reduceyields by 30%. Only in very disease proneconditions (warm and humid, together witha hybrid of lower disease resistance) willthe application of fungicides be economicallybeneficial.Pests can also affect yield. Argentine StemWeevil (ASW), Greasy Cutworm and BlackBeetle can be a problem particularly ifdirect drilling or strip tilling. (chapter seven- Crop Monitoring)Soil structure tends to deteriorate withrepeated cultivation. Compaction reducessoil aeration and aggregation, affecting theability of plant roots to extract water andnutrients from the soil. Paddocks <strong>for</strong>merlyin long term pasture generally have goodsoil structure.8