Effect of Planting Geometries and Fertilizer Placement on Nutrient Uptake by Grain Sorghum

Grain sorghum [Sorghum bicolor (L.) Moench] is an important dryland crop in the Texas Panhandle. Productivity of grain sorghum depends on climatic conditions, plant available soil water, and soil fertility. Previous research has shown growing grain sorghum in clumps instead of Equal Spaced Planting (ESP) reduced plant stress, reduced production of tillers, and increased harvest index and grain yield under dryland conditions. The current study was conducted in the greenhouse and field to investigate the effect of fertilizer application on sorghum plants grown in clump and ESP geometries. The objectives of the research were to (a) compare fertilizer (nitrogen and phosphorus) uptake in grain sorghum plants in clumps and ESP geometries (b) observe root growth patterns in clump and ESP plants (c) and determine the fertilizer effect on tiller formation and harvest index. The greenhouse experiment was conducted at West Texas A&M University during 2014 and 2015. Grain sorghum was grown in clump and ESP geometries with two and three fertilizer levels in 2014 and 2015, respectively. Plants were grown in wooden boxes, with a transparent side, covered by a removable wooden board, so that root growth could be observed. All experiments were conducted in a Randomized complete block design (RCBD) and fertilizer was applied in a band beneath clump and ESP plants. The field experiment was conducted at the USDA Conservation and Production Research Laboratory at Bushland, Texas, during 2014 and 2015. Grain sorghum was grown in clump and ESP planting geometries in unfertilized and fertilized (68 kg N ha-1 and 10 kg P ha-1) plots. Planting density in both geometries was 62,000 plants ha-1. In 2015 corn was grown in clump and ESP planting geometries without using fertilizer. N and P concentrations in grain and stover were obtained from laboratory analysis and data are reported as N uptake in aboveground biomass and P uptake in aboveground biomass In the 2014 greenhouse study, ESP plants had significantly higher N uptake in aboveground biomass, stover yield, and tillers per plant. However, harvest index was higher in clumps. The interaction between planting geometry and fertilizer showed a significantly higher N uptake in ESP with high fertilizer level. In 2015, clump plants had significantly higher grain yield, aboveground N uptake, nitrogen use efficiency (NUE) and phosphorus use efficiency (PUE). Increasing fertilizer level increased P uptake in aboveground biomass. Plants in ESP produced deeper and well developed root systems while clump plants produced roots that developed angularly and then downward. In the 2014 field study, clump plants had lower N and P uptake in aboveground biomass than ESP, but had higher NUE and PUE. Though clump plants had significantly fewer tillers per plant than ESPs, harvest index was not different. In the 2015 field study, planting geometry did not have a significant effect on N and P uptake in aboveground biomass, NUE or PUE. However, the interaction between planting geometry and fertilizer level showed higher N uptake in clump fertilized plants. Clump plants produced fewer tillers per plant. Harvest index was significantly higher in clumps. Fertilized plots had significantly higher N uptake in aboveground biomass but fertilizer had no effect on P uptake. Overall, data suggest N and P uptake in aboveground biomass varies by soil nutrient condition, and level of fertilizer. Increasing fertilizer level increases tiller production in the plants. Application of fertilizer has shown mixed results on N uptake and grain yield in clump and ESP plants. Further investigation is necessary to draw a conclusion on aboveground N and P uptake in plants grown in clump and ESP planting geometries at different fertilizer rates and placement methods.