Assessing the impact of agronomic spacing conditions on biophysical

Introduction

Cotton is the most valuable and major cash crop. It is major source of foreign exchange and plays an important role in agriculture, industry and economic development of the country. The demand of cotton products ensures its survival as world's most widely cultivated crop, despite of the stiff competition given by man-made fibers (Saleem et al., 2010). The crop is grown in about 76 countries which cover more than 32 million hectares of land (Saranga et al., 2001). India along with China, United States, Brazil and Pakistan stand out among the major world cotton producers (United States Department of Agriculture - USDA, 2012). According to a study carried out by International Service for the Acquisition of Agri-biotech Application (ISAAA) it was confirmed that India has overtaken the US to become the second largest cotton producing country in the world, after China. In India, Gujarat has emerged as India's number one cotton producing state. It is the single largest cotton producer state with 36 per cent (101 lakh bales) of the total national production from the area about 25.00 lakh hectares. Among the different districts of Gujarat, Vadodara accounts for 7.7% of the total cotton production of the state.

In cotton, plant spacing affects the growth parameters and yield characteristics of the plant. It is believed to be one of the factor maximizing biophysical, biochemical parameters along with yield and yield components. This may be because cotton yield is believed to be partially determined by crop geometry which is a function of row spacing and plant population. The space available for individual plant growing in field affects the yield and quality of produce and hence proper spacing is one of the key factors resulting into proper and healthy growth of crop (Islam et al., 2011). This important agronomic attribute is also directly related to light interception occurring during photosynthesis (Anyanwu, 2013 and Odabas et al., 2008). Inadequate spacing also leads to clustering of plants and thereby affects photosphere and rhizosphere (Ibeawuchi et al., 2008). Proper spacing improves air flow to plants resulting into moderation of plant temperature and increased photosynthetic levels. It provides right plant density, which refers to the number of plants, allowed on a given unit of land for optimum yield (Obi, 1991). 

The growth and stages of plant are directly influenced by the space available to the plants, although the response is species or cultivar specific (Kirby and Faris, 1970). Plants when are too close to each other, they end up being overcrowded leading later to stunting of the crops thereby ensuing to poor yields. Optimum spacing allows plants to develop to their fullest potential both on top and underneath ground by providing adequate space ensuring less competition for sunlight, water and fertilizers (Sabo et al., 2013). It also aids in the prevention of pests and diseases spread from one plant to another. Researches have been carried out wherein spacing and plant population has enhanced disease and pest management along with weed control and ripping resulting in increasing cotton yield. Although previous studies have been conducted to investigate cotton growth and yield response to row spacing, results are often conflicting.

Realizing the importance of plant spacing, an attempt to understand the relevance of cotton with spacing attribute was made. Performance was assessed in terms of different biochemical parameters i.e chlorophyll content, proline content and biophysical parameters i.e relative water content (RWC), leaf area index (LAI) of cotton crop during different stages of crop growth together with yield and yield components.