Thermal and moisture conditions for maize grain yield creation

The aim of the work was to evaluate the effect of thermodynamical conditions on the grain maize yield elements forming and yield creation. Energy transformations were evaluated according the following changes of internal energy (dU) in critical maize yield forming phases and effect of these changes on the yield in the year with highest and (2002) and the lowest yield (2001). Field polyfactorial experiment was conducted in the years 2001-2003 on the experimental station Dolna Malanta (5 km from Nitra city, south-western region of the Slovak Republic) at the orthic luvisol. Soil porosity in depth 0.30 - 0.40 m is under the critical limit for mentioned soil type. Dot wilting fluctuates in the interval 10-15 %, soil retention and maximal water capacity is favourable. The station is located in the warm and arid agro-climatic region with mild winters. Water supply in soil at the beginning spring is 150-160 mm. Rainfalls deficit 60-90 mm appears from April till May as a result of the retentive balances and saturation accessories increasing. Semi-early grain maize hybrids have high thermal security more than 90%, semilate hybrids have 75-90 % and late hybrids 60-70 %. Medium early hybrid LG-23.06 (FAO 310) with the grain type dentiformis (hybrid type MSC), registered in Slovakia in the year 1998 was used in the experiment. There were three variants of basic soil preparation in the experiment: B1 - conventional tillage (medium ploughing to the 0.20 - 0.25 m depth); B2 - reduced tillage (shallow ploughing to 0.15 - 0.20 m depth); B3 - minimal tillage (dishing to depth 0.10 - 0.15 m). Every tillage variant had three variants of fertilization: NF - unfertilized control variant; F1 - fertilization by industrial fertilizers on the supposed grain harvest 7 t/ha according to the soil nutrients contents; F2 - fertilization by industrial fertilizers on the supposed grain harvest 7 t/ha according to the soil nutrients contents together with plough-in of after harvest. The remains of the forecrop (pea) were in amount 5.0 tons of dry matter per hectare. In all years part of fertilizing was done before the basic soil preparation (15 kg P and 20 kg K/ha). The second part of fertilizing (50 kg N and 44 kg P/ha) was done during the vegetation. Pre-sowing soil preparation was made by rotary tiller MARS. Maize was sown at April 23rd, to the soil depth 60-100 mm, with interline range 700 mm and inline range 180-200 mm. Crop was harvested on 10th September. According to the changes of internal energy critical thermodynamic phase of the crop was determined. Maximal (in year 2002) and minimal harvest (in year 2001) was found. Temperature and water safety was evaluated during the period from sowing to harvest. Agroclimatical and phenological characteristics of the given locality were considered at the calculations. Results were evaluated by analysis of variance. From results follows, that grain maize has two critical thermodynamical stages- May and August. For maximal harvest creation is necessary domination of input energy from rainfalls above the input energy of temperatures, and values of internal energy be negative. The highest water requirements has grain maize 10-25 days before flowering (water at this time influences the set of grain). Optimal sum of rainfalls in this time is 140-145 mm. Overflow of rainfalls in the phase from milk maturity to the yield reduces internal energy of plants and elongates the vegetative stage of growth. Results acquired in the given agroecological conditions indicate necessity of grain maize breeding on drought resistance (also in wider context with expectation of global changes of climatic conditions).