The document investigates the efficiency of complete and incomplete nearest neighbour balanced block designs under second order error correlation structures using generalized least squares estimation. It compares the efficiencies of auto regressive (AR), moving average (MA), and nearest neighbour (NN) models, concluding that for large block sizes with high correlation, generalized least squares can effectively estimate direct and neighbour effects. The research highlights that MA(2) outperforms other models in incomplete block designs, providing significant gains in efficiency over regular block designs.